Adding upstream version 5:7.0.15.upstream/5%7.0.15upstream

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 3051 insertions, 0 deletions

diff --git a/src/acl.c b/src/acl.c
new file mode 100644
index 0000000..6d86093
--- /dev/null
+++ b/src/acl.c
@@ -0,0 +1,3051 @@
+/*
+ * Copyright (c) 2018, Salvatore Sanfilippo <antirez at gmail dot com>
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *
+ *   * Redistributions of source code must retain the above copyright notice,
+ *     this list of conditions and the following disclaimer.
+ *   * Redistributions in binary form must reproduce the above copyright
+ *     notice, this list of conditions and the following disclaimer in the
+ *     documentation and/or other materials provided with the distribution.
+ *   * Neither the name of Redis nor the names of its contributors may be used
+ *     to endorse or promote products derived from this software without
+ *     specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
+ * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
+ * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
+ * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
+ * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
+ * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
+ * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
+ * POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#include "server.h"
+#include "sha256.h"
+#include <fcntl.h>
+#include <ctype.h>
+
+/* =============================================================================
+ * Global state for ACLs
+ * ==========================================================================*/
+
+rax *Users; /* Table mapping usernames to user structures. */
+
+user *DefaultUser;  /* Global reference to the default user.
+                       Every new connection is associated to it, if no
+                       AUTH or HELLO is used to authenticate with a
+                       different user. */
+
+list *UsersToLoad;  /* This is a list of users found in the configuration file
+                       that we'll need to load in the final stage of Redis
+                       initialization, after all the modules are already
+                       loaded. Every list element is a NULL terminated
+                       array of SDS pointers: the first is the user name,
+                       all the remaining pointers are ACL rules in the same
+                       format as ACLSetUser(). */
+list *ACLLog;       /* Our security log, the user is able to inspect that
+                       using the ACL LOG command .*/
+
+static rax *commandId = NULL; /* Command name to id mapping */
+
+static unsigned long nextid = 0; /* Next command id that has not been assigned */
+
+struct ACLCategoryItem {
+    const char *name;
+    uint64_t flag;
+} ACLCommandCategories[] = { /* See redis.conf for details on each category. */
+    {"keyspace", ACL_CATEGORY_KEYSPACE},
+    {"read", ACL_CATEGORY_READ},
+    {"write", ACL_CATEGORY_WRITE},
+    {"set", ACL_CATEGORY_SET},
+    {"sortedset", ACL_CATEGORY_SORTEDSET},
+    {"list", ACL_CATEGORY_LIST},
+    {"hash", ACL_CATEGORY_HASH},
+    {"string", ACL_CATEGORY_STRING},
+    {"bitmap", ACL_CATEGORY_BITMAP},
+    {"hyperloglog", ACL_CATEGORY_HYPERLOGLOG},
+    {"geo", ACL_CATEGORY_GEO},
+    {"stream", ACL_CATEGORY_STREAM},
+    {"pubsub", ACL_CATEGORY_PUBSUB},
+    {"admin", ACL_CATEGORY_ADMIN},
+    {"fast", ACL_CATEGORY_FAST},
+    {"slow", ACL_CATEGORY_SLOW},
+    {"blocking", ACL_CATEGORY_BLOCKING},
+    {"dangerous", ACL_CATEGORY_DANGEROUS},
+    {"connection", ACL_CATEGORY_CONNECTION},
+    {"transaction", ACL_CATEGORY_TRANSACTION},
+    {"scripting", ACL_CATEGORY_SCRIPTING},
+    {NULL,0} /* Terminator. */
+};
+
+struct ACLUserFlag {
+    const char *name;
+    uint64_t flag;
+} ACLUserFlags[] = {
+    /* Note: the order here dictates the emitted order at ACLDescribeUser */
+    {"on", USER_FLAG_ENABLED},
+    {"off", USER_FLAG_DISABLED},
+    {"nopass", USER_FLAG_NOPASS},
+    {"skip-sanitize-payload", USER_FLAG_SANITIZE_PAYLOAD_SKIP},
+    {"sanitize-payload", USER_FLAG_SANITIZE_PAYLOAD},
+    {NULL,0} /* Terminator. */
+};
+
+struct ACLSelectorFlags {
+    const char *name;
+    uint64_t flag;
+} ACLSelectorFlags[] = {
+    /* Note: the order here dictates the emitted order at ACLDescribeUser */
+    {"allkeys", SELECTOR_FLAG_ALLKEYS},
+    {"allchannels", SELECTOR_FLAG_ALLCHANNELS},
+    {"allcommands", SELECTOR_FLAG_ALLCOMMANDS},
+    {NULL,0} /* Terminator. */
+};
+
+/* ACL selectors are private and not exposed outside of acl.c. */
+typedef struct {
+    uint32_t flags; /* See SELECTOR_FLAG_* */
+    /* The bit in allowed_commands is set if this user has the right to
+     * execute this command.
+     *
+     * If the bit for a given command is NOT set and the command has
+     * allowed first-args, Redis will also check allowed_firstargs in order to
+     * understand if the command can be executed. */
+    uint64_t allowed_commands[USER_COMMAND_BITS_COUNT/64];
+    /* allowed_firstargs is used by ACL rules to block access to a command unless a
+     * specific argv[1] is given.
+     *
+     * For each command ID (corresponding to the command bit set in allowed_commands),
+     * This array points to an array of SDS strings, terminated by a NULL pointer,
+     * with all the first-args that are allowed for this command. When no first-arg
+     * matching is used, the field is just set to NULL to avoid allocating
+     * USER_COMMAND_BITS_COUNT pointers. */
+    sds **allowed_firstargs;
+    list *patterns;  /* A list of allowed key patterns. If this field is NULL
+                        the user cannot mention any key in a command, unless
+                        the flag ALLKEYS is set in the user. */
+    list *channels;  /* A list of allowed Pub/Sub channel patterns. If this
+                        field is NULL the user cannot mention any channel in a
+                        `PUBLISH` or [P][UNSUBSCRIBE] command, unless the flag
+                        ALLCHANNELS is set in the user. */
+} aclSelector;
+
+void ACLResetFirstArgsForCommand(aclSelector *selector, unsigned long id);
+void ACLResetFirstArgs(aclSelector *selector);
+void ACLAddAllowedFirstArg(aclSelector *selector, unsigned long id, const char *sub);
+void ACLFreeLogEntry(void *le);
+int ACLSetSelector(aclSelector *selector, const char *op, size_t oplen);
+
+/* The length of the string representation of a hashed password. */
+#define HASH_PASSWORD_LEN (SHA256_BLOCK_SIZE*2)
+
+/* =============================================================================
+ * Helper functions for the rest of the ACL implementation
+ * ==========================================================================*/
+
+/* Return zero if strings are the same, non-zero if they are not.
+ * The comparison is performed in a way that prevents an attacker to obtain
+ * information about the nature of the strings just monitoring the execution
+ * time of the function. Note: The two strings must be the same length.
+ */
+int time_independent_strcmp(char *a, char *b, int len) {
+    int diff = 0;
+    for (int j = 0; j < len; j++) {
+        diff |= (a[j] ^ b[j]);
+    }
+    return diff; /* If zero strings are the same. */
+}
+
+/* Given an SDS string, returns the SHA256 hex representation as a
+ * new SDS string. */
+sds ACLHashPassword(unsigned char *cleartext, size_t len) {
+    SHA256_CTX ctx;
+    unsigned char hash[SHA256_BLOCK_SIZE];
+    char hex[HASH_PASSWORD_LEN];
+    char *cset = "0123456789abcdef";
+
+    sha256_init(&ctx);
+    sha256_update(&ctx,(unsigned char*)cleartext,len);
+    sha256_final(&ctx,hash);
+
+    for (int j = 0; j < SHA256_BLOCK_SIZE; j++) {
+        hex[j*2] = cset[((hash[j]&0xF0)>>4)];
+        hex[j*2+1] = cset[(hash[j]&0xF)];
+    }
+    return sdsnewlen(hex,HASH_PASSWORD_LEN);
+}
+
+/* Given a hash and the hash length, returns C_OK if it is a valid password
+ * hash, or C_ERR otherwise. */
+int ACLCheckPasswordHash(unsigned char *hash, int hashlen) {
+    if (hashlen != HASH_PASSWORD_LEN) {
+        return C_ERR;
+    }
+
+    /* Password hashes can only be characters that represent
+     * hexadecimal values, which are numbers and lowercase
+     * characters 'a' through 'f'. */
+    for(int i = 0; i < HASH_PASSWORD_LEN; i++) {
+        char c = hash[i];
+        if ((c < 'a' || c > 'f') && (c < '0' || c > '9')) {
+            return C_ERR;
+        }
+    }
+    return C_OK;
+}
+
+/* =============================================================================
+ * Low level ACL API
+ * ==========================================================================*/
+
+/* Return 1 if the specified string contains spaces or null characters.
+ * We do this for usernames and key patterns for simpler rewriting of
+ * ACL rules, presentation on ACL list, and to avoid subtle security bugs
+ * that may arise from parsing the rules in presence of escapes.
+ * The function returns 0 if the string has no spaces. */
+int ACLStringHasSpaces(const char *s, size_t len) {
+    for (size_t i = 0; i < len; i++) {
+        if (isspace(s[i]) || s[i] == 0) return 1;
+    }
+    return 0;
+}
+
+/* Given the category name the command returns the corresponding flag, or
+ * zero if there is no match. */
+uint64_t ACLGetCommandCategoryFlagByName(const char *name) {
+    for (int j = 0; ACLCommandCategories[j].flag != 0; j++) {
+        if (!strcasecmp(name,ACLCommandCategories[j].name)) {
+            return ACLCommandCategories[j].flag;
+        }
+    }
+    return 0; /* No match. */
+}
+
+/* Method for searching for a user within a list of user definitions. The
+ * list contains an array of user arguments, and we are only
+ * searching the first argument, the username, for a match. */
+int ACLListMatchLoadedUser(void *definition, void *user) {
+    sds *user_definition = definition;
+    return sdscmp(user_definition[0], user) == 0;
+}
+
+/* Method for passwords/pattern comparison used for the user->passwords list
+ * so that we can search for items with listSearchKey(). */
+int ACLListMatchSds(void *a, void *b) {
+    return sdscmp(a,b) == 0;
+}
+
+/* Method to free list elements from ACL users password/patterns lists. */
+void ACLListFreeSds(void *item) {
+    sdsfree(item);
+}
+
+/* Method to duplicate list elements from ACL users password/patterns lists. */
+void *ACLListDupSds(void *item) {
+    return sdsdup(item);
+}
+
+/* Structure used for handling key patterns with different key
+ * based permissions. */
+typedef struct {
+    int flags; /* The CMD_KEYS_* flags for this key pattern */
+    sds pattern; /* The pattern to match keys against */
+} keyPattern;
+
+/* Create a new key pattern. */
+keyPattern *ACLKeyPatternCreate(sds pattern, int flags) {
+    keyPattern *new = (keyPattern *) zmalloc(sizeof(keyPattern));
+    new->pattern = pattern;
+    new->flags = flags;
+    return new;
+}
+
+/* Free a key pattern and internal structures. */
+void ACLKeyPatternFree(keyPattern *pattern) {
+    sdsfree(pattern->pattern);
+    zfree(pattern);
+}
+
+/* Method for passwords/pattern comparison used for the user->passwords list
+ * so that we can search for items with listSearchKey(). */
+int ACLListMatchKeyPattern(void *a, void *b) {
+    return sdscmp(((keyPattern *) a)->pattern,((keyPattern *) b)->pattern) == 0;
+}
+
+/* Method to free list elements from ACL users password/patterns lists. */
+void ACLListFreeKeyPattern(void *item) {
+    ACLKeyPatternFree(item);
+}
+
+/* Method to duplicate list elements from ACL users password/patterns lists. */
+void *ACLListDupKeyPattern(void *item) {
+    keyPattern *old = (keyPattern *) item;
+    return ACLKeyPatternCreate(sdsdup(old->pattern), old->flags);
+}
+
+/* Append the string representation of a key pattern onto the
+ * provided base string. */
+sds sdsCatPatternString(sds base, keyPattern *pat) {
+    if (pat->flags == ACL_ALL_PERMISSION) {
+        base = sdscatlen(base,"~",1);
+    } else if (pat->flags == ACL_READ_PERMISSION) {
+        base = sdscatlen(base,"%R~",3);
+    } else if (pat->flags == ACL_WRITE_PERMISSION) {
+        base = sdscatlen(base,"%W~",3);
+    } else {
+        serverPanic("Invalid key pattern flag detected");
+    }
+    return sdscatsds(base, pat->pattern);
+}
+
+/* Create an empty selector with the provided set of initial
+ * flags. The selector will be default have no permissions. */
+aclSelector *ACLCreateSelector(int flags) {
+    aclSelector *selector = zmalloc(sizeof(aclSelector));
+    selector->flags = flags | server.acl_pubsub_default;
+    selector->patterns = listCreate();
+    selector->channels = listCreate();
+    selector->allowed_firstargs = NULL;
+
+    listSetMatchMethod(selector->patterns,ACLListMatchKeyPattern);
+    listSetFreeMethod(selector->patterns,ACLListFreeKeyPattern);
+    listSetDupMethod(selector->patterns,ACLListDupKeyPattern);
+    listSetMatchMethod(selector->channels,ACLListMatchSds);
+    listSetFreeMethod(selector->channels,ACLListFreeSds);
+    listSetDupMethod(selector->channels,ACLListDupSds);
+    memset(selector->allowed_commands,0,sizeof(selector->allowed_commands));
+
+    return selector;
+}
+
+/* Cleanup the provided selector, including all interior structures. */
+void ACLFreeSelector(aclSelector *selector) {
+    listRelease(selector->patterns);
+    listRelease(selector->channels);
+    ACLResetFirstArgs(selector);
+    zfree(selector);
+}
+
+/* Create an exact copy of the provided selector. */
+aclSelector *ACLCopySelector(aclSelector *src) {
+    aclSelector *dst = zmalloc(sizeof(aclSelector));
+    dst->flags = src->flags;
+    dst->patterns = listDup(src->patterns);
+    dst->channels = listDup(src->channels);
+    memcpy(dst->allowed_commands,src->allowed_commands,
+           sizeof(dst->allowed_commands));
+    dst->allowed_firstargs = NULL;
+    /* Copy the allowed first-args array of array of SDS strings. */
+    if (src->allowed_firstargs) {
+        for (int j = 0; j < USER_COMMAND_BITS_COUNT; j++) {
+            if (!(src->allowed_firstargs[j])) continue;
+            for (int i = 0; src->allowed_firstargs[j][i]; i++) {
+                ACLAddAllowedFirstArg(dst, j, src->allowed_firstargs[j][i]);
+            }
+        }
+    }
+    return dst;
+}
+
+/* List method for freeing a selector */
+void ACLListFreeSelector(void *a) {
+    ACLFreeSelector((aclSelector *) a);
+}
+
+/* List method for duplicating a selector */
+void *ACLListDuplicateSelector(void *src) {
+    return ACLCopySelector((aclSelector *)src);
+}
+
+/* All users have an implicit root selector which
+ * provides backwards compatibility to the old ACLs-
+ * permissions. */
+aclSelector *ACLUserGetRootSelector(user *u) {
+    serverAssert(listLength(u->selectors));
+    aclSelector *s = (aclSelector *) listNodeValue(listFirst(u->selectors));
+    serverAssert(s->flags & SELECTOR_FLAG_ROOT);
+    return s;
+}
+
+/* Create a new user with the specified name, store it in the list
+ * of users (the Users global radix tree), and returns a reference to
+ * the structure representing the user.
+ *
+ * If the user with such name already exists NULL is returned. */
+user *ACLCreateUser(const char *name, size_t namelen) {
+    if (raxFind(Users,(unsigned char*)name,namelen) != raxNotFound) return NULL;
+    user *u = zmalloc(sizeof(*u));
+    u->name = sdsnewlen(name,namelen);
+    u->flags = USER_FLAG_DISABLED;
+    u->passwords = listCreate();
+    u->acl_string = NULL;
+    listSetMatchMethod(u->passwords,ACLListMatchSds);
+    listSetFreeMethod(u->passwords,ACLListFreeSds);
+    listSetDupMethod(u->passwords,ACLListDupSds);
+
+    u->selectors = listCreate();
+    listSetFreeMethod(u->selectors,ACLListFreeSelector);
+    listSetDupMethod(u->selectors,ACLListDuplicateSelector);
+
+    /* Add the initial root selector */
+    aclSelector *s = ACLCreateSelector(SELECTOR_FLAG_ROOT);
+    listAddNodeHead(u->selectors, s);
+
+    raxInsert(Users,(unsigned char*)name,namelen,u,NULL);
+    return u;
+}
+
+/* This function should be called when we need an unlinked "fake" user
+ * we can use in order to validate ACL rules or for other similar reasons.
+ * The user will not get linked to the Users radix tree. The returned
+ * user should be released with ACLFreeUser() as usually. */
+user *ACLCreateUnlinkedUser(void) {
+    char username[64];
+    for (int j = 0; ; j++) {
+        snprintf(username,sizeof(username),"__fakeuser:%d__",j);
+        user *fakeuser = ACLCreateUser(username,strlen(username));
+        if (fakeuser == NULL) continue;
+        int retval = raxRemove(Users,(unsigned char*) username,
+                               strlen(username),NULL);
+        serverAssert(retval != 0);
+        return fakeuser;
+    }
+}
+
+/* Release the memory used by the user structure. Note that this function
+ * will not remove the user from the Users global radix tree. */
+void ACLFreeUser(user *u) {
+    sdsfree(u->name);
+    if (u->acl_string) {
+        decrRefCount(u->acl_string);
+        u->acl_string = NULL;
+    }
+    listRelease(u->passwords);
+    listRelease(u->selectors);
+    zfree(u);
+}
+
+/* When a user is deleted we need to cycle the active
+ * connections in order to kill all the pending ones that
+ * are authenticated with such user. */
+void ACLFreeUserAndKillClients(user *u) {
+    listIter li;
+    listNode *ln;
+    listRewind(server.clients,&li);
+    while ((ln = listNext(&li)) != NULL) {
+        client *c = listNodeValue(ln);
+        if (c->user == u) {
+            /* We'll free the connection asynchronously, so
+             * in theory to set a different user is not needed.
+             * However if there are bugs in Redis, soon or later
+             * this may result in some security hole: it's much
+             * more defensive to set the default user and put
+             * it in non authenticated mode. */
+            c->user = DefaultUser;
+            c->authenticated = 0;
+            /* We will write replies to this client later, so we can't
+             * close it directly even if async. */
+            if (c == server.current_client) {
+                c->flags |= CLIENT_CLOSE_AFTER_COMMAND;
+            } else {
+                freeClientAsync(c);
+            }
+        }
+    }
+    ACLFreeUser(u);
+}
+
+/* Copy the user ACL rules from the source user 'src' to the destination
+ * user 'dst' so that at the end of the process they'll have exactly the
+ * same rules (but the names will continue to be the original ones). */
+void ACLCopyUser(user *dst, user *src) {
+    listRelease(dst->passwords);
+    listRelease(dst->selectors);
+    dst->passwords = listDup(src->passwords);
+    dst->selectors = listDup(src->selectors);
+    dst->flags = src->flags;
+    if (dst->acl_string) {
+        decrRefCount(dst->acl_string);
+    }
+    dst->acl_string = src->acl_string;
+    if (dst->acl_string) {
+        /* if src is NULL, we set it to NULL, if not, need to increment reference count */
+        incrRefCount(dst->acl_string);
+    }
+}
+
+/* Free all the users registered in the radix tree 'users' and free the
+ * radix tree itself. */
+void ACLFreeUsersSet(rax *users) {
+    raxFreeWithCallback(users,(void(*)(void*))ACLFreeUserAndKillClients);
+}
+
+/* Given a command ID, this function set by reference 'word' and 'bit'
+ * so that user->allowed_commands[word] will address the right word
+ * where the corresponding bit for the provided ID is stored, and
+ * so that user->allowed_commands[word]&bit will identify that specific
+ * bit. The function returns C_ERR in case the specified ID overflows
+ * the bitmap in the user representation. */
+int ACLGetCommandBitCoordinates(uint64_t id, uint64_t *word, uint64_t *bit) {
+    if (id >= USER_COMMAND_BITS_COUNT) return C_ERR;
+    *word = id / sizeof(uint64_t) / 8;
+    *bit = 1ULL << (id % (sizeof(uint64_t) * 8));
+    return C_OK;
+}
+
+/* Check if the specified command bit is set for the specified user.
+ * The function returns 1 is the bit is set or 0 if it is not.
+ * Note that this function does not check the ALLCOMMANDS flag of the user
+ * but just the lowlevel bitmask.
+ *
+ * If the bit overflows the user internal representation, zero is returned
+ * in order to disallow the execution of the command in such edge case. */
+int ACLGetSelectorCommandBit(const aclSelector *selector, unsigned long id) {
+    uint64_t word, bit;
+    if (ACLGetCommandBitCoordinates(id,&word,&bit) == C_ERR) return 0;
+    return (selector->allowed_commands[word] & bit) != 0;
+}
+
+/* When +@all or allcommands is given, we set a reserved bit as well that we
+ * can later test, to see if the user has the right to execute "future commands",
+ * that is, commands loaded later via modules. */
+int ACLSelectorCanExecuteFutureCommands(aclSelector *selector) {
+    return ACLGetSelectorCommandBit(selector,USER_COMMAND_BITS_COUNT-1);
+}
+
+/* Set the specified command bit for the specified user to 'value' (0 or 1).
+ * If the bit overflows the user internal representation, no operation
+ * is performed. As a side effect of calling this function with a value of
+ * zero, the user flag ALLCOMMANDS is cleared since it is no longer possible
+ * to skip the command bit explicit test. */
+void ACLSetSelectorCommandBit(aclSelector *selector, unsigned long id, int value) {
+    uint64_t word, bit;
+    if (ACLGetCommandBitCoordinates(id,&word,&bit) == C_ERR) return;
+    if (value) {
+        selector->allowed_commands[word] |= bit;
+    } else {
+        selector->allowed_commands[word] &= ~bit;
+        selector->flags &= ~SELECTOR_FLAG_ALLCOMMANDS;
+    }
+}
+
+/* This function is used to allow/block a specific command.
+ * Allowing/blocking a container command also applies for its subcommands */
+void ACLChangeSelectorPerm(aclSelector *selector, struct redisCommand *cmd, int allow) {
+    unsigned long id = cmd->id;
+    ACLSetSelectorCommandBit(selector,id,allow);
+    ACLResetFirstArgsForCommand(selector,id);
+    if (cmd->subcommands_dict) {
+        dictEntry *de;
+        dictIterator *di = dictGetSafeIterator(cmd->subcommands_dict);
+        while((de = dictNext(di)) != NULL) {
+            struct redisCommand *sub = (struct redisCommand *)dictGetVal(de);
+            ACLSetSelectorCommandBit(selector,sub->id,allow);
+        }
+        dictReleaseIterator(di);
+    }
+}
+
+void ACLSetSelectorCommandBitsForCategoryLogic(dict *commands, aclSelector *selector, uint64_t cflag, int value) {
+    dictIterator *di = dictGetIterator(commands);
+    dictEntry *de;
+    while ((de = dictNext(di)) != NULL) {
+        struct redisCommand *cmd = dictGetVal(de);
+        if (cmd->flags & CMD_MODULE) continue; /* Ignore modules commands. */
+        if (cmd->acl_categories & cflag) {
+            ACLChangeSelectorPerm(selector,cmd,value);
+        }
+        if (cmd->subcommands_dict) {
+            ACLSetSelectorCommandBitsForCategoryLogic(cmd->subcommands_dict, selector, cflag, value);
+        }
+    }
+    dictReleaseIterator(di);
+}
+
+/* This is like ACLSetSelectorCommandBit(), but instead of setting the specified
+ * ID, it will check all the commands in the category specified as argument,
+ * and will set all the bits corresponding to such commands to the specified
+ * value. Since the category passed by the user may be non existing, the
+ * function returns C_ERR if the category was not found, or C_OK if it was
+ * found and the operation was performed. */
+int ACLSetSelectorCommandBitsForCategory(aclSelector *selector, const char *category, int value) {
+    uint64_t cflag = ACLGetCommandCategoryFlagByName(category);
+    if (!cflag) return C_ERR;
+    ACLSetSelectorCommandBitsForCategoryLogic(server.orig_commands, selector, cflag, value);
+    return C_OK;
+}
+
+void ACLCountCategoryBitsForCommands(dict *commands, aclSelector *selector, unsigned long *on, unsigned long *off, uint64_t cflag) {
+    dictIterator *di = dictGetIterator(commands);
+    dictEntry *de;
+    while ((de = dictNext(di)) != NULL) {
+        struct redisCommand *cmd = dictGetVal(de);
+        if (cmd->acl_categories & cflag) {
+            if (ACLGetSelectorCommandBit(selector,cmd->id))
+                (*on)++;
+            else
+                (*off)++;
+        }
+        if (cmd->subcommands_dict) {
+            ACLCountCategoryBitsForCommands(cmd->subcommands_dict, selector, on, off, cflag);
+        }
+    }
+    dictReleaseIterator(di);
+}
+
+/* Return the number of commands allowed (on) and denied (off) for the user 'u'
+ * in the subset of commands flagged with the specified category name.
+ * If the category name is not valid, C_ERR is returned, otherwise C_OK is
+ * returned and on and off are populated by reference. */
+int ACLCountCategoryBitsForSelector(aclSelector *selector, unsigned long *on, unsigned long *off,
+                                const char *category)
+{
+    uint64_t cflag = ACLGetCommandCategoryFlagByName(category);
+    if (!cflag) return C_ERR;
+
+    *on = *off = 0;
+    ACLCountCategoryBitsForCommands(server.orig_commands, selector, on, off, cflag);
+    return C_OK;
+}
+
+sds ACLDescribeSelectorCommandRulesSingleCommands(aclSelector *selector, aclSelector *fake_selector,
+        sds rules, dict *commands) {
+    dictIterator *di = dictGetIterator(commands);
+    dictEntry *de;
+    while ((de = dictNext(di)) != NULL) {
+        struct redisCommand *cmd = dictGetVal(de);
+        int userbit = ACLGetSelectorCommandBit(selector,cmd->id);
+        int fakebit = ACLGetSelectorCommandBit(fake_selector,cmd->id);
+        if (userbit != fakebit) {
+            rules = sdscatlen(rules, userbit ? "+" : "-", 1);
+            rules = sdscatsds(rules,cmd->fullname);
+            rules = sdscatlen(rules," ",1);
+            ACLChangeSelectorPerm(fake_selector,cmd,userbit);
+        }
+
+        if (cmd->subcommands_dict)
+            rules = ACLDescribeSelectorCommandRulesSingleCommands(selector,fake_selector,rules,cmd->subcommands_dict);
+
+        /* Emit the first-args if there are any. */
+        if (userbit == 0 && selector->allowed_firstargs &&
+            selector->allowed_firstargs[cmd->id])
+        {
+            for (int j = 0; selector->allowed_firstargs[cmd->id][j]; j++) {
+                rules = sdscatlen(rules,"+",1);
+                rules = sdscatsds(rules,cmd->fullname);
+                rules = sdscatlen(rules,"|",1);
+                rules = sdscatsds(rules,selector->allowed_firstargs[cmd->id][j]);
+                rules = sdscatlen(rules," ",1);
+            }
+        }
+    }
+    dictReleaseIterator(di);
+    return rules;
+}
+
+/* This function returns an SDS string representing the specified selector ACL
+ * rules related to command execution, in the same format you could set them
+ * back using ACL SETUSER. The function will return just the set of rules needed
+ * to recreate the user commands bitmap, without including other user flags such
+ * as on/off, passwords and so forth. The returned string always starts with
+ * the +@all or -@all rule, depending on the user bitmap, and is followed, if
+ * needed, by the other rules needed to narrow or extend what the user can do. */
+sds ACLDescribeSelectorCommandRules(aclSelector *selector) {
+    sds rules = sdsempty();
+    int additive;   /* If true we start from -@all and add, otherwise if
+                       false we start from +@all and remove. */
+
+    /* This code is based on a trick: as we generate the rules, we apply
+     * them to a fake user, so that as we go we still know what are the
+     * bit differences we should try to address by emitting more rules. */
+    aclSelector fs = {0};
+    aclSelector *fake_selector = &fs;
+
+    /* Here we want to understand if we should start with +@all and remove
+     * the commands corresponding to the bits that are not set in the user
+     * commands bitmap, or the contrary. Note that semantically the two are
+     * different. For instance starting with +@all and subtracting, the user
+     * will be able to execute future commands, while -@all and adding will just
+     * allow the user the run the selected commands and/or categories.
+     * How do we test for that? We use the trick of a reserved command ID bit
+     * that is set only by +@all (and its alias "allcommands"). */
+    if (ACLSelectorCanExecuteFutureCommands(selector)) {
+        additive = 0;
+        rules = sdscat(rules,"+@all ");
+        ACLSetSelector(fake_selector,"+@all",-1);
+    } else {
+        additive = 1;
+        rules = sdscat(rules,"-@all ");
+        ACLSetSelector(fake_selector,"-@all",-1);
+    }
+
+    /* Attempt to find a good approximation for categories and commands
+     * based on the current bits used, by looping over the category list
+     * and applying the best fit each time. Often a set of categories will not 
+     * perfectly match the set of commands into it, so at the end we do a 
+     * final pass adding/removing the single commands needed to make the bitmap
+     * exactly match. A temp user is maintained to keep track of categories 
+     * already applied. */
+    aclSelector ts = {0};
+    aclSelector *temp_selector = &ts;
+    
+    /* Keep track of the categories that have been applied, to prevent
+     * applying them twice.  */
+    char applied[sizeof(ACLCommandCategories)/sizeof(ACLCommandCategories[0])];
+    memset(applied, 0, sizeof(applied));
+
+    memcpy(temp_selector->allowed_commands,
+        selector->allowed_commands, 
+        sizeof(selector->allowed_commands));
+    while (1) {
+        int best = -1;
+        unsigned long mindiff = INT_MAX, maxsame = 0;
+        for (int j = 0; ACLCommandCategories[j].flag != 0; j++) {
+            if (applied[j]) continue;
+
+            unsigned long on, off, diff, same;
+            ACLCountCategoryBitsForSelector(temp_selector,&on,&off,ACLCommandCategories[j].name);
+            /* Check if the current category is the best this loop:
+             * * It has more commands in common with the user than commands
+             *   that are different.
+             * AND EITHER
+             * * It has the fewest number of differences
+             *    than the best match we have found so far. 
+             * * OR it matches the fewest number of differences
+             *   that we've seen but it has more in common. */
+            diff = additive ? off : on;
+            same = additive ? on : off;
+            if (same > diff && 
+                ((diff < mindiff) || (diff == mindiff && same > maxsame)))
+            {
+                best = j;
+                mindiff = diff;
+                maxsame = same;
+            }
+        }
+
+        /* We didn't find a match */
+        if (best == -1) break;
+
+        sds op = sdsnewlen(additive ? "+@" : "-@", 2);
+        op = sdscat(op,ACLCommandCategories[best].name);
+        ACLSetSelector(fake_selector,op,-1);
+
+        sds invop = sdsnewlen(additive ? "-@" : "+@", 2);
+        invop = sdscat(invop,ACLCommandCategories[best].name);
+        ACLSetSelector(temp_selector,invop,-1);
+
+        rules = sdscatsds(rules,op);
+        rules = sdscatlen(rules," ",1);
+        sdsfree(op);
+        sdsfree(invop);
+
+        applied[best] = 1;
+    }
+
+    /* Fix the final ACLs with single commands differences. */
+    rules = ACLDescribeSelectorCommandRulesSingleCommands(selector,fake_selector,rules,server.orig_commands);
+
+    /* Trim the final useless space. */
+    sdsrange(rules,0,-2);
+
+    /* This is technically not needed, but we want to verify that now the
+     * predicted bitmap is exactly the same as the user bitmap, and abort
+     * otherwise, because aborting is better than a security risk in this
+     * code path. */
+    if (memcmp(fake_selector->allowed_commands,
+                        selector->allowed_commands,
+                        sizeof(selector->allowed_commands)) != 0)
+    {
+        serverLog(LL_WARNING,
+            "CRITICAL ERROR: User ACLs don't match final bitmap: '%s'",
+            rules);
+        serverPanic("No bitmap match in ACLDescribeSelectorCommandRules()");
+    }
+    return rules;
+}
+
+sds ACLDescribeSelector(aclSelector *selector) {
+    listIter li;
+    listNode *ln;
+    sds res = sdsempty();
+    /* Key patterns. */
+    if (selector->flags & SELECTOR_FLAG_ALLKEYS) {
+        res = sdscatlen(res,"~* ",3);
+    } else {
+        listRewind(selector->patterns,&li);
+        while((ln = listNext(&li))) {
+            keyPattern *thispat = (keyPattern *)listNodeValue(ln);
+            res = sdsCatPatternString(res, thispat);
+            res = sdscatlen(res," ",1);
+        }
+    }
+
+    /* Pub/sub channel patterns. */
+    if (selector->flags & SELECTOR_FLAG_ALLCHANNELS) {
+        res = sdscatlen(res,"&* ",3);
+    } else {
+        res = sdscatlen(res,"resetchannels ",14);
+        listRewind(selector->channels,&li);
+        while((ln = listNext(&li))) {
+            sds thispat = listNodeValue(ln);
+            res = sdscatlen(res,"&",1);
+            res = sdscatsds(res,thispat);
+            res = sdscatlen(res," ",1);
+        }
+    }
+
+    /* Command rules. */
+    sds rules = ACLDescribeSelectorCommandRules(selector);
+    res = sdscatsds(res,rules);
+    sdsfree(rules);
+    return res;
+}
+
+/* This is similar to ACLDescribeSelectorCommandRules(), however instead of
+ * describing just the user command rules, everything is described: user
+ * flags, keys, passwords and finally the command rules obtained via
+ * the ACLDescribeSelectorCommandRules() function. This is the function we call
+ * when we want to rewrite the configuration files describing ACLs and
+ * in order to show users with ACL LIST. */
+robj *ACLDescribeUser(user *u) {
+    if (u->acl_string) {
+        incrRefCount(u->acl_string);
+        return u->acl_string;
+    }
+
+    sds res = sdsempty();
+
+    /* Flags. */
+    for (int j = 0; ACLUserFlags[j].flag; j++) {
+        if (u->flags & ACLUserFlags[j].flag) {
+            res = sdscat(res,ACLUserFlags[j].name);
+            res = sdscatlen(res," ",1);
+        }
+    }
+
+    /* Passwords. */
+    listIter li;
+    listNode *ln;
+    listRewind(u->passwords,&li);
+    while((ln = listNext(&li))) {
+        sds thispass = listNodeValue(ln);
+        res = sdscatlen(res,"#",1);
+        res = sdscatsds(res,thispass);
+        res = sdscatlen(res," ",1);
+    }
+
+    /* Selectors (Commands and keys) */
+    listRewind(u->selectors,&li);
+    while((ln = listNext(&li))) {
+        aclSelector *selector = (aclSelector *) listNodeValue(ln);
+        sds default_perm = ACLDescribeSelector(selector);
+        if (selector->flags & SELECTOR_FLAG_ROOT) {
+            res = sdscatfmt(res, "%s", default_perm);
+        } else {
+            res = sdscatfmt(res, " (%s)", default_perm);
+        }
+        sdsfree(default_perm);
+    }
+
+    u->acl_string = createObject(OBJ_STRING, res);
+    /* because we are returning it, have to increase count */
+    incrRefCount(u->acl_string);
+
+    return u->acl_string;
+}
+
+/* Get a command from the original command table, that is not affected
+ * by the command renaming operations: we base all the ACL work from that
+ * table, so that ACLs are valid regardless of command renaming. */
+struct redisCommand *ACLLookupCommand(const char *name) {
+    struct redisCommand *cmd;
+    sds sdsname = sdsnew(name);
+    cmd = lookupCommandBySdsLogic(server.orig_commands,sdsname);
+    sdsfree(sdsname);
+    return cmd;
+}
+
+/* Flush the array of allowed first-args for the specified user
+ * and command ID. */
+void ACLResetFirstArgsForCommand(aclSelector *selector, unsigned long id) {
+    if (selector->allowed_firstargs && selector->allowed_firstargs[id]) {
+        for (int i = 0; selector->allowed_firstargs[id][i]; i++)
+            sdsfree(selector->allowed_firstargs[id][i]);
+        zfree(selector->allowed_firstargs[id]);
+        selector->allowed_firstargs[id] = NULL;
+    }
+}
+
+/* Flush the entire table of first-args. This is useful on +@all, -@all
+ * or similar to return back to the minimal memory usage (and checks to do)
+ * for the user. */
+void ACLResetFirstArgs(aclSelector *selector) {
+    if (selector->allowed_firstargs == NULL) return;
+    for (int j = 0; j < USER_COMMAND_BITS_COUNT; j++) {
+        if (selector->allowed_firstargs[j]) {
+            for (int i = 0; selector->allowed_firstargs[j][i]; i++)
+                sdsfree(selector->allowed_firstargs[j][i]);
+            zfree(selector->allowed_firstargs[j]);
+        }
+    }
+    zfree(selector->allowed_firstargs);
+    selector->allowed_firstargs = NULL;
+}
+
+/* Add a first-arh to the list of subcommands for the user 'u' and
+ * the command id specified. */
+void ACLAddAllowedFirstArg(aclSelector *selector, unsigned long id, const char *sub) {
+    /* If this is the first first-arg to be configured for
+     * this user, we have to allocate the first-args array. */
+    if (selector->allowed_firstargs == NULL) {
+        selector->allowed_firstargs = zcalloc(USER_COMMAND_BITS_COUNT * sizeof(sds*));
+    }
+
+    /* We also need to enlarge the allocation pointing to the
+     * null terminated SDS array, to make space for this one.
+     * To start check the current size, and while we are here
+     * make sure the first-arg is not already specified inside. */
+    long items = 0;
+    if (selector->allowed_firstargs[id]) {
+        while(selector->allowed_firstargs[id][items]) {
+            /* If it's already here do not add it again. */
+            if (!strcasecmp(selector->allowed_firstargs[id][items],sub))
+                return;
+            items++;
+        }
+    }
+
+    /* Now we can make space for the new item (and the null term). */
+    items += 2;
+    selector->allowed_firstargs[id] = zrealloc(selector->allowed_firstargs[id], sizeof(sds)*items);
+    selector->allowed_firstargs[id][items-2] = sdsnew(sub);
+    selector->allowed_firstargs[id][items-1] = NULL;
+}
+
+/* Create an ACL selector from the given ACL operations, which should be 
+ * a list of space separate ACL operations that starts and ends 
+ * with parentheses.
+ *
+ * If any of the operations are invalid, NULL will be returned instead
+ * and errno will be set corresponding to the interior error. */
+aclSelector *aclCreateSelectorFromOpSet(const char *opset, size_t opsetlen) {
+    serverAssert(opset[0] == '(' && opset[opsetlen - 1] == ')');
+    aclSelector *s = ACLCreateSelector(0);
+
+    int argc = 0;
+    sds trimmed = sdsnewlen(opset + 1, opsetlen - 2);
+    sds *argv = sdssplitargs(trimmed, &argc);
+    for (int i = 0; i < argc; i++) {
+        if (ACLSetSelector(s, argv[i], sdslen(argv[i])) == C_ERR) {
+            ACLFreeSelector(s);
+            s = NULL;
+            goto cleanup;
+        }
+    }
+
+cleanup:
+    sdsfreesplitres(argv, argc);
+    sdsfree(trimmed);
+    return s;
+}
+
+/* Set a selector's properties with the provided 'op'.
+ *
+ * +<command>   Allow the execution of that command.
+ *              May be used with `|` for allowing subcommands (e.g "+config|get")
+ * -<command>   Disallow the execution of that command.
+ *              May be used with `|` for blocking subcommands (e.g "-config|set")
+ * +@<category> Allow the execution of all the commands in such category
+ *              with valid categories are like @admin, @set, @sortedset, ...
+ *              and so forth, see the full list in the server.c file where
+ *              the Redis command table is described and defined.
+ *              The special category @all means all the commands, but currently
+ *              present in the server, and that will be loaded in the future
+ *              via modules.
+ * +<command>|first-arg    Allow a specific first argument of an otherwise
+ *                         disabled command. Note that this form is not
+ *                         allowed as negative like -SELECT|1, but
+ *                         only additive starting with "+".
+ * allcommands  Alias for +@all. Note that it implies the ability to execute
+ *              all the future commands loaded via the modules system.
+ * nocommands   Alias for -@all.
+ * ~<pattern>   Add a pattern of keys that can be mentioned as part of
+ *              commands. For instance ~* allows all the keys. The pattern
+ *              is a glob-style pattern like the one of KEYS.
+ *              It is possible to specify multiple patterns.
+ * %R~<pattern> Add key read pattern that specifies which keys can be read
+ *              from.
+ * %W~<pattern> Add key write pattern that specifies which keys can be
+ *              written to.
+ * allkeys      Alias for ~*
+ * resetkeys    Flush the list of allowed keys patterns.
+ * &<pattern>   Add a pattern of channels that can be mentioned as part of
+ *              Pub/Sub commands. For instance &* allows all the channels. The
+ *              pattern is a glob-style pattern like the one of PSUBSCRIBE.
+ *              It is possible to specify multiple patterns.
+ * allchannels              Alias for &*
+ * resetchannels            Flush the list of allowed channel patterns.
+ */
+int ACLSetSelector(aclSelector *selector, const char* op, size_t oplen) {
+    if (!strcasecmp(op,"allkeys") ||
+               !strcasecmp(op,"~*"))
+    {
+        selector->flags |= SELECTOR_FLAG_ALLKEYS;
+        listEmpty(selector->patterns);
+    } else if (!strcasecmp(op,"resetkeys")) {
+        selector->flags &= ~SELECTOR_FLAG_ALLKEYS;
+        listEmpty(selector->patterns);
+    } else if (!strcasecmp(op,"allchannels") ||
+               !strcasecmp(op,"&*"))
+    {
+        selector->flags |= SELECTOR_FLAG_ALLCHANNELS;
+        listEmpty(selector->channels);
+    } else if (!strcasecmp(op,"resetchannels")) {
+        selector->flags &= ~SELECTOR_FLAG_ALLCHANNELS;
+        listEmpty(selector->channels);
+    } else if (!strcasecmp(op,"allcommands") ||
+               !strcasecmp(op,"+@all"))
+    {
+        memset(selector->allowed_commands,255,sizeof(selector->allowed_commands));
+        selector->flags |= SELECTOR_FLAG_ALLCOMMANDS;
+        ACLResetFirstArgs(selector);
+    } else if (!strcasecmp(op,"nocommands") ||
+               !strcasecmp(op,"-@all"))
+    {
+        memset(selector->allowed_commands,0,sizeof(selector->allowed_commands));
+        selector->flags &= ~SELECTOR_FLAG_ALLCOMMANDS;
+        ACLResetFirstArgs(selector);
+    } else if (op[0] == '~' || op[0] == '%') {
+        if (selector->flags & SELECTOR_FLAG_ALLKEYS) {
+            errno = EEXIST;
+            return C_ERR;
+        }
+        int flags = 0;
+        size_t offset = 1;
+        if (op[0] == '%') {
+            for (; offset < oplen; offset++) {
+                if (toupper(op[offset]) == 'R' && !(flags & ACL_READ_PERMISSION)) {
+                    flags |= ACL_READ_PERMISSION;
+                } else if (toupper(op[offset]) == 'W' && !(flags & ACL_WRITE_PERMISSION)) {
+                    flags |= ACL_WRITE_PERMISSION;
+                } else if (op[offset] == '~') {
+                    offset++;
+                    break;
+                } else {
+                    errno = EINVAL;
+                    return C_ERR;
+                }
+            }
+        } else {
+            flags = ACL_ALL_PERMISSION;
+        }
+
+        if (ACLStringHasSpaces(op+offset,oplen-offset)) {
+            errno = EINVAL;
+            return C_ERR;
+        }
+        keyPattern *newpat = ACLKeyPatternCreate(sdsnewlen(op+offset,oplen-offset), flags);
+        listNode *ln = listSearchKey(selector->patterns,newpat);
+        /* Avoid re-adding the same key pattern multiple times. */
+        if (ln == NULL) {
+            listAddNodeTail(selector->patterns,newpat);
+        } else {
+            ((keyPattern *)listNodeValue(ln))->flags |= flags;
+            ACLKeyPatternFree(newpat);
+        }
+        selector->flags &= ~SELECTOR_FLAG_ALLKEYS;
+    } else if (op[0] == '&') {
+        if (selector->flags & SELECTOR_FLAG_ALLCHANNELS) {
+            errno = EISDIR;
+            return C_ERR;
+        }
+        if (ACLStringHasSpaces(op+1,oplen-1)) {
+            errno = EINVAL;
+            return C_ERR;
+        }
+        sds newpat = sdsnewlen(op+1,oplen-1);
+        listNode *ln = listSearchKey(selector->channels,newpat);
+        /* Avoid re-adding the same channel pattern multiple times. */
+        if (ln == NULL)
+            listAddNodeTail(selector->channels,newpat);
+        else
+            sdsfree(newpat);
+        selector->flags &= ~SELECTOR_FLAG_ALLCHANNELS;
+    } else if (op[0] == '+' && op[1] != '@') {
+        if (strrchr(op,'|') == NULL) {
+            struct redisCommand *cmd = ACLLookupCommand(op+1);
+            if (cmd == NULL) {
+                errno = ENOENT;
+                return C_ERR;
+            }
+            ACLChangeSelectorPerm(selector,cmd,1);
+        } else {
+            /* Split the command and subcommand parts. */
+            char *copy = zstrdup(op+1);
+            char *sub = strrchr(copy,'|');
+            sub[0] = '\0';
+            sub++;
+
+            struct redisCommand *cmd = ACLLookupCommand(copy);
+
+            /* Check if the command exists. We can't check the
+             * first-arg to see if it is valid. */
+            if (cmd == NULL) {
+                zfree(copy);
+                errno = ENOENT;
+                return C_ERR;
+            }
+
+            /* We do not support allowing first-arg of a subcommand */
+            if (cmd->parent) {
+                zfree(copy);
+                errno = ECHILD;
+                return C_ERR;
+            }
+
+            /* The subcommand cannot be empty, so things like DEBUG|
+             * are syntax errors of course. */
+            if (strlen(sub) == 0) {
+                zfree(copy);
+                errno = EINVAL;
+                return C_ERR;
+            }
+
+            if (cmd->subcommands_dict) {
+                /* If user is trying to allow a valid subcommand we can just add its unique ID */
+                cmd = ACLLookupCommand(op+1);
+                if (cmd == NULL) {
+                    zfree(copy);
+                    errno = ENOENT;
+                    return C_ERR;
+                }
+                ACLChangeSelectorPerm(selector,cmd,1);
+            } else {
+                /* If user is trying to use the ACL mech to block SELECT except SELECT 0 or
+                 * block DEBUG except DEBUG OBJECT (DEBUG subcommands are not considered
+                 * subcommands for now) we use the allowed_firstargs mechanism. */
+
+                /* Add the first-arg to the list of valid ones. */
+                serverLog(LL_WARNING, "Deprecation warning: Allowing a first arg of an otherwise "
+                                      "blocked command is a misuse of ACL and may get disabled "
+                                      "in the future (offender: +%s)", op+1);
+                ACLAddAllowedFirstArg(selector,cmd->id,sub);
+            }
+
+            zfree(copy);
+        }
+    } else if (op[0] == '-' && op[1] != '@') {
+        struct redisCommand *cmd = ACLLookupCommand(op+1);
+        if (cmd == NULL) {
+            errno = ENOENT;
+            return C_ERR;
+        }
+        ACLChangeSelectorPerm(selector,cmd,0);
+    } else if ((op[0] == '+' || op[0] == '-') && op[1] == '@') {
+        int bitval = op[0] == '+' ? 1 : 0;
+        if (ACLSetSelectorCommandBitsForCategory(selector,op+2,bitval) == C_ERR) {
+            errno = ENOENT;
+            return C_ERR;
+        }
+    } else {
+        errno = EINVAL;
+        return C_ERR;
+    }
+    return C_OK;
+}
+
+/* Set user properties according to the string "op". The following
+ * is a description of what different strings will do:
+ *
+ * on           Enable the user: it is possible to authenticate as this user.
+ * off          Disable the user: it's no longer possible to authenticate
+ *              with this user, however the already authenticated connections
+ *              will still work.
+ * ><password>  Add this password to the list of valid password for the user.
+ *              For example >mypass will add "mypass" to the list.
+ *              This directive clears the "nopass" flag (see later).
+ * #<hash>      Add this password hash to the list of valid hashes for
+ *              the user. This is useful if you have previously computed
+ *              the hash, and don't want to store it in plaintext.
+ *              This directive clears the "nopass" flag (see later).
+ * <<password>  Remove this password from the list of valid passwords.
+ * !<hash>      Remove this hashed password from the list of valid passwords.
+ *              This is useful when you want to remove a password just by
+ *              hash without knowing its plaintext version at all.
+ * nopass       All the set passwords of the user are removed, and the user
+ *              is flagged as requiring no password: it means that every
+ *              password will work against this user. If this directive is
+ *              used for the default user, every new connection will be
+ *              immediately authenticated with the default user without
+ *              any explicit AUTH command required. Note that the "resetpass"
+ *              directive will clear this condition.
+ * resetpass    Flush the list of allowed passwords. Moreover removes the
+ *              "nopass" status. After "resetpass" the user has no associated
+ *              passwords and there is no way to authenticate without adding
+ *              some password (or setting it as "nopass" later).
+ * reset        Performs the following actions: resetpass, resetkeys, off,
+ *              -@all. The user returns to the same state it has immediately
+ *              after its creation.
+ * (<options>)  Create a new selector with the options specified within the
+ *              parentheses and attach it to the user. Each option should be
+ *              space separated. The first character must be ( and the last
+ *              character must be ).
+ * clearselectors          Remove all of the currently attached selectors. 
+ *                         Note this does not change the "root" user permissions,
+ *                         which are the permissions directly applied onto the
+ *                         user (outside the parentheses).
+ * 
+ * Selector options can also be specified by this function, in which case
+ * they update the root selector for the user.
+ *
+ * The 'op' string must be null terminated. The 'oplen' argument should
+ * specify the length of the 'op' string in case the caller requires to pass
+ * binary data (for instance the >password form may use a binary password).
+ * Otherwise the field can be set to -1 and the function will use strlen()
+ * to determine the length.
+ *
+ * The function returns C_OK if the action to perform was understood because
+ * the 'op' string made sense. Otherwise C_ERR is returned if the operation
+ * is unknown or has some syntax error.
+ *
+ * When an error is returned, errno is set to the following values:
+ *
+ * EINVAL: The specified opcode is not understood or the key/channel pattern is
+ *         invalid (contains non allowed characters).
+ * ENOENT: The command name or command category provided with + or - is not
+ *         known.
+ * EEXIST: You are adding a key pattern after "*" was already added. This is
+ *         almost surely an error on the user side.
+ * EISDIR: You are adding a channel pattern after "*" was already added. This is
+ *         almost surely an error on the user side.
+ * ENODEV: The password you are trying to remove from the user does not exist.
+ * EBADMSG: The hash you are trying to add is not a valid hash.
+ * ECHILD: Attempt to allow a specific first argument of a subcommand
+ */
+int ACLSetUser(user *u, const char *op, ssize_t oplen) {
+    /* as we are changing the ACL, the old generated string is now invalid */
+    if (u->acl_string) {
+        decrRefCount(u->acl_string);
+        u->acl_string = NULL;
+    }
+
+    if (oplen == -1) oplen = strlen(op);
+    if (oplen == 0) return C_OK; /* Empty string is a no-operation. */
+    if (!strcasecmp(op,"on")) {
+        u->flags |= USER_FLAG_ENABLED;
+        u->flags &= ~USER_FLAG_DISABLED;
+    } else if (!strcasecmp(op,"off")) {
+        u->flags |= USER_FLAG_DISABLED;
+        u->flags &= ~USER_FLAG_ENABLED;
+    } else if (!strcasecmp(op,"skip-sanitize-payload")) {
+        u->flags |= USER_FLAG_SANITIZE_PAYLOAD_SKIP;
+        u->flags &= ~USER_FLAG_SANITIZE_PAYLOAD;
+    } else if (!strcasecmp(op,"sanitize-payload")) {
+        u->flags &= ~USER_FLAG_SANITIZE_PAYLOAD_SKIP;
+        u->flags |= USER_FLAG_SANITIZE_PAYLOAD;
+    } else if (!strcasecmp(op,"nopass")) {
+        u->flags |= USER_FLAG_NOPASS;
+        listEmpty(u->passwords);
+    } else if (!strcasecmp(op,"resetpass")) {
+        u->flags &= ~USER_FLAG_NOPASS;
+        listEmpty(u->passwords);
+    } else if (op[0] == '>' || op[0] == '#') {
+        sds newpass;
+        if (op[0] == '>') {
+            newpass = ACLHashPassword((unsigned char*)op+1,oplen-1);
+        } else {
+            if (ACLCheckPasswordHash((unsigned char*)op+1,oplen-1) == C_ERR) {
+                errno = EBADMSG;
+                return C_ERR;
+            }
+            newpass = sdsnewlen(op+1,oplen-1);
+        }
+
+        listNode *ln = listSearchKey(u->passwords,newpass);
+        /* Avoid re-adding the same password multiple times. */
+        if (ln == NULL)
+            listAddNodeTail(u->passwords,newpass);
+        else
+            sdsfree(newpass);
+        u->flags &= ~USER_FLAG_NOPASS;
+    } else if (op[0] == '<' || op[0] == '!') {
+        sds delpass;
+        if (op[0] == '<') {
+            delpass = ACLHashPassword((unsigned char*)op+1,oplen-1);
+        } else {
+            if (ACLCheckPasswordHash((unsigned char*)op+1,oplen-1) == C_ERR) {
+                errno = EBADMSG;
+                return C_ERR;
+            }
+            delpass = sdsnewlen(op+1,oplen-1);
+        }
+        listNode *ln = listSearchKey(u->passwords,delpass);
+        sdsfree(delpass);
+        if (ln) {
+            listDelNode(u->passwords,ln);
+        } else {
+            errno = ENODEV;
+            return C_ERR;
+        }
+    } else if (op[0] == '(' && op[oplen - 1] == ')') {
+        aclSelector *selector = aclCreateSelectorFromOpSet(op, oplen);
+        if (!selector) {
+            /* No errorno set, propagate it from interior error. */
+            return C_ERR;
+        }
+        listAddNodeTail(u->selectors, selector);
+        return C_OK;
+    } else if (!strcasecmp(op,"clearselectors")) {
+        listIter li;
+        listNode *ln;
+        listRewind(u->selectors,&li);
+        /* There has to be a root selector */
+        serverAssert(listNext(&li));
+        while((ln = listNext(&li))) {
+            listDelNode(u->selectors, ln);
+        }
+        return C_OK;
+    } else if (!strcasecmp(op,"reset")) {
+        serverAssert(ACLSetUser(u,"resetpass",-1) == C_OK);
+        serverAssert(ACLSetUser(u,"resetkeys",-1) == C_OK);
+        serverAssert(ACLSetUser(u,"resetchannels",-1) == C_OK);
+        if (server.acl_pubsub_default & SELECTOR_FLAG_ALLCHANNELS)
+            serverAssert(ACLSetUser(u,"allchannels",-1) == C_OK);
+        serverAssert(ACLSetUser(u,"off",-1) == C_OK);
+        serverAssert(ACLSetUser(u,"sanitize-payload",-1) == C_OK);
+        serverAssert(ACLSetUser(u,"clearselectors",-1) == C_OK);
+        serverAssert(ACLSetUser(u,"-@all",-1) == C_OK);
+    } else {
+        aclSelector *selector = ACLUserGetRootSelector(u);
+        if (ACLSetSelector(selector, op, oplen) == C_ERR) {
+            return C_ERR;
+        }
+    }
+    return C_OK;
+}
+
+/* Return a description of the error that occurred in ACLSetUser() according to
+ * the errno value set by the function on error. */
+const char *ACLSetUserStringError(void) {
+    const char *errmsg = "Wrong format";
+    if (errno == ENOENT)
+        errmsg = "Unknown command or category name in ACL";
+    else if (errno == EINVAL)
+        errmsg = "Syntax error";
+    else if (errno == EEXIST)
+        errmsg = "Adding a pattern after the * pattern (or the "
+                 "'allkeys' flag) is not valid and does not have any "
+                 "effect. Try 'resetkeys' to start with an empty "
+                 "list of patterns";
+    else if (errno == EISDIR)
+        errmsg = "Adding a pattern after the * pattern (or the "
+                 "'allchannels' flag) is not valid and does not have any "
+                 "effect. Try 'resetchannels' to start with an empty "
+                 "list of channels";
+    else if (errno == ENODEV)
+        errmsg = "The password you are trying to remove from the user does "
+                 "not exist";
+    else if (errno == EBADMSG)
+        errmsg = "The password hash must be exactly 64 characters and contain "
+                 "only lowercase hexadecimal characters";
+    else if (errno == EALREADY)
+        errmsg = "Duplicate user found. A user can only be defined once in "
+                 "config files";
+    else if (errno == ECHILD)
+        errmsg = "Allowing first-arg of a subcommand is not supported";
+    return errmsg;
+}
+
+/* Create the default user, this has special permissions. */
+user *ACLCreateDefaultUser(void) {
+    user *new = ACLCreateUser("default",7);
+    ACLSetUser(new,"+@all",-1);
+    ACLSetUser(new,"~*",-1);
+    ACLSetUser(new,"&*",-1);
+    ACLSetUser(new,"on",-1);
+    ACLSetUser(new,"nopass",-1);
+    return new;
+}
+
+/* Initialization of the ACL subsystem. */
+void ACLInit(void) {
+    Users = raxNew();
+    UsersToLoad = listCreate();
+    listSetMatchMethod(UsersToLoad, ACLListMatchLoadedUser);
+    ACLLog = listCreate();
+    DefaultUser = ACLCreateDefaultUser();
+}
+
+/* Check the username and password pair and return C_OK if they are valid,
+ * otherwise C_ERR is returned and errno is set to:
+ *
+ *  EINVAL: if the username-password do not match.
+ *  ENONENT: if the specified user does not exist at all.
+ */
+int ACLCheckUserCredentials(robj *username, robj *password) {
+    user *u = ACLGetUserByName(username->ptr,sdslen(username->ptr));
+    if (u == NULL) {
+        errno = ENOENT;
+        return C_ERR;
+    }
+
+    /* Disabled users can't login. */
+    if (u->flags & USER_FLAG_DISABLED) {
+        errno = EINVAL;
+        return C_ERR;
+    }
+
+    /* If the user is configured to don't require any password, we
+     * are already fine here. */
+    if (u->flags & USER_FLAG_NOPASS) return C_OK;
+
+    /* Check all the user passwords for at least one to match. */
+    listIter li;
+    listNode *ln;
+    listRewind(u->passwords,&li);
+    sds hashed = ACLHashPassword(password->ptr,sdslen(password->ptr));
+    while((ln = listNext(&li))) {
+        sds thispass = listNodeValue(ln);
+        if (!time_independent_strcmp(hashed, thispass, HASH_PASSWORD_LEN)) {
+            sdsfree(hashed);
+            return C_OK;
+        }
+    }
+    sdsfree(hashed);
+
+    /* If we reached this point, no password matched. */
+    errno = EINVAL;
+    return C_ERR;
+}
+
+/* This is like ACLCheckUserCredentials(), however if the user/pass
+ * are correct, the connection is put in authenticated state and the
+ * connection user reference is populated.
+ *
+ * The return value is C_OK or C_ERR with the same meaning as
+ * ACLCheckUserCredentials(). */
+int ACLAuthenticateUser(client *c, robj *username, robj *password) {
+    if (ACLCheckUserCredentials(username,password) == C_OK) {
+        c->authenticated = 1;
+        c->user = ACLGetUserByName(username->ptr,sdslen(username->ptr));
+        moduleNotifyUserChanged(c);
+        return C_OK;
+    } else {
+        addACLLogEntry(c,ACL_DENIED_AUTH,(c->flags & CLIENT_MULTI) ? ACL_LOG_CTX_MULTI : ACL_LOG_CTX_TOPLEVEL,0,username->ptr,NULL);
+        return C_ERR;
+    }
+}
+
+/* For ACL purposes, every user has a bitmap with the commands that such
+ * user is allowed to execute. In order to populate the bitmap, every command
+ * should have an assigned ID (that is used to index the bitmap). This function
+ * creates such an ID: it uses sequential IDs, reusing the same ID for the same
+ * command name, so that a command retains the same ID in case of modules that
+ * are unloaded and later reloaded.
+ *
+ * The function does not take ownership of the 'cmdname' SDS string.
+ * */
+unsigned long ACLGetCommandID(sds cmdname) {
+    sds lowername = sdsdup(cmdname);
+    sdstolower(lowername);
+    if (commandId == NULL) commandId = raxNew();
+    void *id = raxFind(commandId,(unsigned char*)lowername,sdslen(lowername));
+    if (id != raxNotFound) {
+        sdsfree(lowername);
+        return (unsigned long)id;
+    }
+    raxInsert(commandId,(unsigned char*)lowername,strlen(lowername),
+              (void*)nextid,NULL);
+    sdsfree(lowername);
+    unsigned long thisid = nextid;
+    nextid++;
+
+    /* We never assign the last bit in the user commands bitmap structure,
+     * this way we can later check if this bit is set, understanding if the
+     * current ACL for the user was created starting with a +@all to add all
+     * the possible commands and just subtracting other single commands or
+     * categories, or if, instead, the ACL was created just adding commands
+     * and command categories from scratch, not allowing future commands by
+     * default (loaded via modules). This is useful when rewriting the ACLs
+     * with ACL SAVE. */
+    if (nextid == USER_COMMAND_BITS_COUNT-1) nextid++;
+    return thisid;
+}
+
+/* Clear command id table and reset nextid to 0. */
+void ACLClearCommandID(void) {
+    if (commandId) raxFree(commandId);
+    commandId = NULL;
+    nextid = 0;
+}
+
+/* Return an username by its name, or NULL if the user does not exist. */
+user *ACLGetUserByName(const char *name, size_t namelen) {
+    void *myuser = raxFind(Users,(unsigned char*)name,namelen);
+    if (myuser == raxNotFound) return NULL;
+    return myuser;
+}
+
+/* =============================================================================
+ * ACL permission checks
+ * ==========================================================================*/
+
+/* Check if the key can be accessed by the selector.
+ *
+ * If the selector can access the key, ACL_OK is returned, otherwise
+ * ACL_DENIED_KEY is returned. */
+static int ACLSelectorCheckKey(aclSelector *selector, const char *key, int keylen, int keyspec_flags) {
+    /* The selector can access any key */
+    if (selector->flags & SELECTOR_FLAG_ALLKEYS) return ACL_OK;
+
+    listIter li;
+    listNode *ln;
+    listRewind(selector->patterns,&li);
+
+    int key_flags = 0;
+    if (keyspec_flags & CMD_KEY_ACCESS) key_flags |= ACL_READ_PERMISSION;
+    if (keyspec_flags & CMD_KEY_INSERT) key_flags |= ACL_WRITE_PERMISSION;
+    if (keyspec_flags & CMD_KEY_DELETE) key_flags |= ACL_WRITE_PERMISSION;
+    if (keyspec_flags & CMD_KEY_UPDATE) key_flags |= ACL_WRITE_PERMISSION;
+
+    /* Test this key against every pattern. */
+    while((ln = listNext(&li))) {
+        keyPattern *pattern = listNodeValue(ln);
+        if ((pattern->flags & key_flags) != key_flags)
+            continue;
+        size_t plen = sdslen(pattern->pattern);
+        if (stringmatchlen(pattern->pattern,plen,key,keylen,0))
+            return ACL_OK;
+    }
+    return ACL_DENIED_KEY;
+}
+
+/* Checks if the provided selector selector has access specified in flags
+ * to all keys in the keyspace. For example, CMD_KEY_READ access requires either
+ * '%R~*', '~*', or allkeys to be granted to the selector. Returns 1 if all 
+ * the access flags are satisfied with this selector or 0 otherwise.
+ */
+static int ACLSelectorHasUnrestrictedKeyAccess(aclSelector *selector, int flags) {
+    /* The selector can access any key */
+    if (selector->flags & SELECTOR_FLAG_ALLKEYS) return 1;
+
+    listIter li;
+    listNode *ln;
+    listRewind(selector->patterns,&li);
+
+    int access_flags = 0;
+    if (flags & CMD_KEY_ACCESS) access_flags |= ACL_READ_PERMISSION;
+    if (flags & CMD_KEY_INSERT) access_flags |= ACL_WRITE_PERMISSION;
+    if (flags & CMD_KEY_DELETE) access_flags |= ACL_WRITE_PERMISSION;
+    if (flags & CMD_KEY_UPDATE) access_flags |= ACL_WRITE_PERMISSION;
+
+    /* Test this key against every pattern. */
+    while((ln = listNext(&li))) {
+        keyPattern *pattern = listNodeValue(ln);
+        if ((pattern->flags & access_flags) != access_flags)
+            continue;
+        if (!strcmp(pattern->pattern,"*")) {
+           return 1;
+       }
+    }
+    return 0;
+}
+
+/* Checks a channel against a provided list of channels. The is_pattern 
+ * argument should only be used when subscribing (not when publishing)
+ * and controls whether the input channel is evaluated as a channel pattern
+ * (like in PSUBSCRIBE) or a plain channel name (like in SUBSCRIBE). 
+ * 
+ * Note that a plain channel name like in PUBLISH or SUBSCRIBE can be
+ * matched against ACL channel patterns, but the pattern provided in PSUBSCRIBE
+ * can only be matched as a literal against an ACL pattern (using plain string compare). */
+static int ACLCheckChannelAgainstList(list *reference, const char *channel, int channellen, int is_pattern) {
+    listIter li;
+    listNode *ln;
+
+    listRewind(reference, &li);
+    while((ln = listNext(&li))) {
+        sds pattern = listNodeValue(ln);
+        size_t plen = sdslen(pattern);
+        /* Channel patterns are matched literally against the channels in
+         * the list. Regular channels perform pattern matching. */
+        if ((is_pattern && !strcmp(pattern,channel)) || 
+            (!is_pattern && stringmatchlen(pattern,plen,channel,channellen,0)))
+        {
+            return ACL_OK;
+        }
+    }
+    return ACL_DENIED_CHANNEL;
+}
+
+/* To prevent duplicate calls to getKeysResult, a cache is maintained
+ * in between calls to the various selectors. */
+typedef struct {
+    int keys_init;
+    getKeysResult keys;
+} aclKeyResultCache;
+
+void initACLKeyResultCache(aclKeyResultCache *cache) {
+    cache->keys_init = 0;
+}
+
+void cleanupACLKeyResultCache(aclKeyResultCache *cache) {
+    if (cache->keys_init) getKeysFreeResult(&(cache->keys));
+}
+
+/* Check if the command is ready to be executed according to the
+ * ACLs associated with the specified selector.
+ *
+ * If the selector can execute the command ACL_OK is returned, otherwise
+ * ACL_DENIED_CMD, ACL_DENIED_KEY, or ACL_DENIED_CHANNEL is returned: the first in case the
+ * command cannot be executed because the selector is not allowed to run such
+ * command, the second and third if the command is denied because the selector is trying
+ * to access a key or channel that are not among the specified patterns. */
+static int ACLSelectorCheckCmd(aclSelector *selector, struct redisCommand *cmd, robj **argv, int argc, int *keyidxptr, aclKeyResultCache *cache) {
+    uint64_t id = cmd->id;
+    int ret;
+    if (!(selector->flags & SELECTOR_FLAG_ALLCOMMANDS) && !(cmd->flags & CMD_NO_AUTH)) {
+        /* If the bit is not set we have to check further, in case the
+         * command is allowed just with that specific first argument. */
+        if (ACLGetSelectorCommandBit(selector,id) == 0) {
+            /* Check if the first argument matches. */
+            if (argc < 2 ||
+                selector->allowed_firstargs == NULL ||
+                selector->allowed_firstargs[id] == NULL)
+            {
+                return ACL_DENIED_CMD;
+            }
+
+            long subid = 0;
+            while (1) {
+                if (selector->allowed_firstargs[id][subid] == NULL)
+                    return ACL_DENIED_CMD;
+                int idx = cmd->parent ? 2 : 1;
+                if (!strcasecmp(argv[idx]->ptr,selector->allowed_firstargs[id][subid]))
+                    break; /* First argument match found. Stop here. */
+                subid++;
+            }
+        }
+    }
+
+    /* Check if the user can execute commands explicitly touching the keys
+     * mentioned in the command arguments. */
+    if (!(selector->flags & SELECTOR_FLAG_ALLKEYS) && doesCommandHaveKeys(cmd)) {
+        if (!(cache->keys_init)) {
+            cache->keys = (getKeysResult) GETKEYS_RESULT_INIT;
+            getKeysFromCommandWithSpecs(cmd, argv, argc, GET_KEYSPEC_DEFAULT, &(cache->keys));
+            cache->keys_init = 1;
+        }
+        getKeysResult *result = &(cache->keys);
+        keyReference *resultidx = result->keys;
+        for (int j = 0; j < result->numkeys; j++) {
+            int idx = resultidx[j].pos;
+            ret = ACLSelectorCheckKey(selector, argv[idx]->ptr, sdslen(argv[idx]->ptr), resultidx[j].flags);
+            if (ret != ACL_OK) {
+                if (keyidxptr) *keyidxptr = resultidx[j].pos;
+                return ret;
+            }
+        }
+    }
+
+    /* Check if the user can execute commands explicitly touching the channels
+     * mentioned in the command arguments */
+    const int channel_flags = CMD_CHANNEL_PUBLISH | CMD_CHANNEL_SUBSCRIBE;
+    if (!(selector->flags & SELECTOR_FLAG_ALLCHANNELS) && doesCommandHaveChannelsWithFlags(cmd, channel_flags)) {
+        getKeysResult channels = (getKeysResult) GETKEYS_RESULT_INIT;
+        getChannelsFromCommand(cmd, argv, argc, &channels);
+        keyReference *channelref = channels.keys;
+        for (int j = 0; j < channels.numkeys; j++) {
+            int idx = channelref[j].pos;
+            if (!(channelref[j].flags & channel_flags)) continue;
+            int is_pattern = channelref[j].flags & CMD_CHANNEL_PATTERN;
+            int ret = ACLCheckChannelAgainstList(selector->channels, argv[idx]->ptr, sdslen(argv[idx]->ptr), is_pattern);
+            if (ret != ACL_OK) {
+                if (keyidxptr) *keyidxptr = channelref[j].pos;
+                getKeysFreeResult(&channels);
+                return ret;
+            }
+        }
+        getKeysFreeResult(&channels);
+    }
+    return ACL_OK;
+}
+
+/* Check if the key can be accessed by the client according to
+ * the ACLs associated with the specified user according to the
+ * keyspec access flags.
+ *
+ * If the user can access the key, ACL_OK is returned, otherwise
+ * ACL_DENIED_KEY is returned. */
+int ACLUserCheckKeyPerm(user *u, const char *key, int keylen, int flags) {
+    listIter li;
+    listNode *ln;
+
+    /* If there is no associated user, the connection can run anything. */
+    if (u == NULL) return ACL_OK;
+
+    /* Check all of the selectors */
+    listRewind(u->selectors,&li);
+    while((ln = listNext(&li))) {
+        aclSelector *s = (aclSelector *) listNodeValue(ln);
+        if (ACLSelectorCheckKey(s, key, keylen, flags) == ACL_OK) {
+            return ACL_OK;
+        }
+    }
+    return ACL_DENIED_KEY;
+}
+
+/* Checks if the user can execute the given command with the added restriction
+ * it must also have the access specified in flags to any key in the key space. 
+ * For example, CMD_KEY_READ access requires either '%R~*', '~*', or allkeys to be 
+ * granted in addition to the access required by the command. Returns 1 
+ * if the user has access or 0 otherwise.
+ */
+int ACLUserCheckCmdWithUnrestrictedKeyAccess(user *u, struct redisCommand *cmd, robj **argv, int argc, int flags) {
+    listIter li;
+    listNode *ln;
+    int local_idxptr;
+
+    /* If there is no associated user, the connection can run anything. */
+    if (u == NULL) return 1;
+
+    /* For multiple selectors, we cache the key result in between selector
+     * calls to prevent duplicate lookups. */
+    aclKeyResultCache cache;
+    initACLKeyResultCache(&cache);
+
+    /* Check each selector sequentially */
+    listRewind(u->selectors,&li);
+    while((ln = listNext(&li))) {
+        aclSelector *s = (aclSelector *) listNodeValue(ln);
+        int acl_retval = ACLSelectorCheckCmd(s, cmd, argv, argc, &local_idxptr, &cache);
+        if (acl_retval == ACL_OK && ACLSelectorHasUnrestrictedKeyAccess(s, flags)) {
+            cleanupACLKeyResultCache(&cache);
+            return 1;
+        }
+    }
+    cleanupACLKeyResultCache(&cache);
+    return 0;
+}
+
+/* Check if the channel can be accessed by the client according to
+ * the ACLs associated with the specified user.
+ *
+ * If the user can access the key, ACL_OK is returned, otherwise
+ * ACL_DENIED_CHANNEL is returned. */
+int ACLUserCheckChannelPerm(user *u, sds channel, int is_pattern) {
+    listIter li;
+    listNode *ln;
+
+    /* If there is no associated user, the connection can run anything. */
+    if (u == NULL) return ACL_OK;
+
+    /* Check all of the selectors */
+    listRewind(u->selectors,&li);
+    while((ln = listNext(&li))) {
+        aclSelector *s = (aclSelector *) listNodeValue(ln);
+        /* The selector can run any keys */
+        if (s->flags & SELECTOR_FLAG_ALLCHANNELS) return ACL_OK;
+
+        /* Otherwise, loop over the selectors list and check each channel */
+        if (ACLCheckChannelAgainstList(s->channels, channel, sdslen(channel), is_pattern) == ACL_OK) {
+            return ACL_OK;
+        }
+    }
+    return ACL_DENIED_CHANNEL;
+}
+
+/* Lower level API that checks if a specified user is able to execute a given command. */
+int ACLCheckAllUserCommandPerm(user *u, struct redisCommand *cmd, robj **argv, int argc, int *idxptr) {
+    listIter li;
+    listNode *ln;
+
+    /* If there is no associated user, the connection can run anything. */
+    if (u == NULL) return ACL_OK;
+
+    /* We have to pick a single error to log, the logic for picking is as follows:
+     * 1) If no selector can execute the command, return the command.
+     * 2) Return the last key or channel that no selector could match. */
+    int relevant_error = ACL_DENIED_CMD;
+    int local_idxptr = 0, last_idx = 0;
+
+    /* For multiple selectors, we cache the key result in between selector
+     * calls to prevent duplicate lookups. */
+    aclKeyResultCache cache;
+    initACLKeyResultCache(&cache);
+
+    /* Check each selector sequentially */
+    listRewind(u->selectors,&li);
+    while((ln = listNext(&li))) {
+        aclSelector *s = (aclSelector *) listNodeValue(ln);
+        int acl_retval = ACLSelectorCheckCmd(s, cmd, argv, argc, &local_idxptr, &cache);
+        if (acl_retval == ACL_OK) {
+            cleanupACLKeyResultCache(&cache);
+            return ACL_OK;
+        }
+        if (acl_retval > relevant_error ||
+            (acl_retval == relevant_error && local_idxptr > last_idx))
+        {
+            relevant_error = acl_retval;
+            last_idx = local_idxptr;
+        }
+    }
+
+    *idxptr = last_idx;
+    cleanupACLKeyResultCache(&cache);
+    return relevant_error;
+}
+
+/* High level API for checking if a client can execute the queued up command */
+int ACLCheckAllPerm(client *c, int *idxptr) {
+    return ACLCheckAllUserCommandPerm(c->user, c->cmd, c->argv, c->argc, idxptr);
+}
+
+/* Check if the user's existing pub/sub clients violate the ACL pub/sub
+ * permissions specified via the upcoming argument, and kill them if so. */
+void ACLKillPubsubClientsIfNeeded(user *new, user *original) {
+    listIter li, lpi;
+    listNode *ln, *lpn;
+    robj *o;
+    int kill = 0;
+    
+    /* First optimization is we check if any selector has all channel
+     * permissions. */
+    listRewind(new->selectors,&li);
+    while((ln = listNext(&li))) {
+        aclSelector *s = (aclSelector *) listNodeValue(ln);
+        if (s->flags & SELECTOR_FLAG_ALLCHANNELS) return;
+    }
+
+    /* Second optimization is to check if the new list of channels
+     * is a strict superset of the original. This is done by
+     * created an "upcoming" list of all channels that are in
+     * the new user and checking each of the existing channels
+     * against it.  */
+    list *upcoming = listCreate();
+    listRewind(new->selectors,&li);
+    while((ln = listNext(&li))) {
+        aclSelector *s = (aclSelector *) listNodeValue(ln);
+        listRewind(s->channels, &lpi);
+        while((lpn = listNext(&lpi))) {
+            listAddNodeTail(upcoming, listNodeValue(lpn));
+        }
+    }
+
+    int match = 1;
+    listRewind(original->selectors,&li);
+    while((ln = listNext(&li)) && match) {
+        aclSelector *s = (aclSelector *) listNodeValue(ln);
+        /* If any of the original selectors has the all-channels permission, but
+         * the new ones don't (this is checked earlier in this function), then the
+         * new list is not a strict superset of the original.  */
+        if (s->flags & SELECTOR_FLAG_ALLCHANNELS) {
+            match = 0;
+            break;
+        }
+        listRewind(s->channels, &lpi);
+        while((lpn = listNext(&lpi)) && match) {
+            if (!listSearchKey(upcoming, listNodeValue(lpn))) {
+                match = 0;
+                break;
+            }
+        }
+    }
+
+    if (match) {
+        /* All channels were matched, no need to kill clients. */
+        listRelease(upcoming);
+        return;
+    }
+    
+    /* Permissions have changed, so we need to iterate through all
+     * the clients and disconnect those that are no longer valid.
+     * Scan all connected clients to find the user's pub/subs. */
+    listRewind(server.clients,&li);
+    while ((ln = listNext(&li)) != NULL) {
+        client *c = listNodeValue(ln);
+        kill = 0;
+
+        if (c->user == original && getClientType(c) == CLIENT_TYPE_PUBSUB) {
+            /* Check for pattern violations. */
+            listRewind(c->pubsub_patterns,&lpi);
+            while (!kill && ((lpn = listNext(&lpi)) != NULL)) {
+
+                o = lpn->value;
+                int res = ACLCheckChannelAgainstList(upcoming, o->ptr, sdslen(o->ptr), 1);
+                kill = (res == ACL_DENIED_CHANNEL);
+            }
+            /* Check for channel violations. */
+            if (!kill) {
+                /* Check for global channels violation. */
+                dictIterator *di = dictGetIterator(c->pubsub_channels);
+
+                dictEntry *de;                
+                while (!kill && ((de = dictNext(di)) != NULL)) {
+                    o = dictGetKey(de);
+                    int res = ACLCheckChannelAgainstList(upcoming, o->ptr, sdslen(o->ptr), 0);
+                    kill = (res == ACL_DENIED_CHANNEL);
+                }
+                dictReleaseIterator(di);
+
+                /* Check for shard channels violation. */
+                di = dictGetIterator(c->pubsubshard_channels);
+                while (!kill && ((de = dictNext(di)) != NULL)) {
+                    o = dictGetKey(de);
+                    int res = ACLCheckChannelAgainstList(upcoming, o->ptr, sdslen(o->ptr), 0);
+                    kill = (res == ACL_DENIED_CHANNEL);
+                }
+
+                dictReleaseIterator(di);
+            }
+
+            /* Kill it. */
+            if (kill) {
+                freeClient(c);
+            }
+        }
+    }
+    listRelease(upcoming);
+}
+
+/* =============================================================================
+ * ACL loading / saving functions
+ * ==========================================================================*/
+
+
+/* Selector definitions should be sent as a single argument, however
+ * we will be lenient and try to find selector definitions spread 
+ * across multiple arguments since it makes for a simpler user experience
+ * for ACL SETUSER as well as when loading from conf files. 
+ * 
+ * This function takes in an array of ACL operators, excluding the username,
+ * and merges selector operations that are spread across multiple arguments. The return
+ * value is a new SDS array, with length set to the passed in merged_argc. Arguments 
+ * that are untouched are still duplicated. If there is an unmatched parenthesis, NULL 
+ * is returned and invalid_idx is set to the argument with the start of the opening
+ * parenthesis. */
+sds *ACLMergeSelectorArguments(sds *argv, int argc, int *merged_argc, int *invalid_idx) {
+    *merged_argc = 0;
+    int open_bracket_start = -1;
+
+    sds *acl_args = (sds *) zmalloc(sizeof(sds) * argc);
+
+    sds selector = NULL;
+    for (int j = 0; j < argc; j++) {
+        char *op = argv[j];
+
+        if (op[0] == '(' && op[sdslen(op) - 1] != ')') {
+            selector = sdsdup(argv[j]);
+            open_bracket_start = j;
+            continue;
+        }
+
+        if (open_bracket_start != -1) {
+            selector = sdscatfmt(selector, " %s", op);
+            if (op[sdslen(op) - 1] == ')') {
+                open_bracket_start = -1;
+                acl_args[*merged_argc] = selector;                        
+                (*merged_argc)++;
+            }
+            continue;
+        }
+
+        acl_args[*merged_argc] = sdsdup(argv[j]);
+        (*merged_argc)++;
+    }
+
+    if (open_bracket_start != -1) {
+        for (int i = 0; i < *merged_argc; i++) sdsfree(acl_args[i]);
+        zfree(acl_args);
+        sdsfree(selector);
+        if (invalid_idx) *invalid_idx = open_bracket_start;
+        return NULL;
+    }
+
+    return acl_args;
+}
+
+/* takes an acl string already split on spaces and adds it to the given user
+ * if the user object is NULL, will create a user with the given username
+ *
+ * Returns an error as an sds string if the ACL string is not parsable
+ */
+sds ACLStringSetUser(user *u, sds username, sds *argv, int argc) {
+    serverAssert(u != NULL || username != NULL);
+
+    sds error = NULL;
+
+    int merged_argc = 0, invalid_idx = 0;
+    sds *acl_args = ACLMergeSelectorArguments(argv, argc, &merged_argc, &invalid_idx);
+
+    if (!acl_args) {
+        return sdscatfmt(sdsempty(),
+                         "Unmatched parenthesis in acl selector starting "
+                         "at '%s'.", (char *) argv[invalid_idx]);
+    }
+
+    /* Create a temporary user to validate and stage all changes against
+     * before applying to an existing user or creating a new user. If all
+     * arguments are valid the user parameters will all be applied together.
+     * If there are any errors then none of the changes will be applied. */
+    user *tempu = ACLCreateUnlinkedUser();
+    if (u) {
+        ACLCopyUser(tempu, u);
+    }
+
+    for (int j = 0; j < merged_argc; j++) {
+        if (ACLSetUser(tempu,acl_args[j],(ssize_t) sdslen(acl_args[j])) != C_OK) {
+            const char *errmsg = ACLSetUserStringError();
+            error = sdscatfmt(sdsempty(),
+                              "Error in ACL SETUSER modifier '%s': %s",
+                              (char*)acl_args[j], errmsg);
+            goto cleanup;
+        }
+    }
+
+    /* Existing pub/sub clients authenticated with the user may need to be
+     * disconnected if (some of) their channel permissions were revoked. */
+    if (u) {
+        ACLKillPubsubClientsIfNeeded(tempu, u);
+    }
+
+    /* Overwrite the user with the temporary user we modified above. */
+    if (!u) {
+        u = ACLCreateUser(username,sdslen(username));
+    }
+    serverAssert(u != NULL);
+
+    ACLCopyUser(u, tempu);
+
+cleanup:
+    ACLFreeUser(tempu);
+    for (int i = 0; i < merged_argc; i++) {
+        sdsfree(acl_args[i]);
+    }
+    zfree(acl_args);
+
+    return error;
+}
+
+/* Given an argument vector describing a user in the form:
+ *
+ *      user <username> ... ACL rules and flags ...
+ *
+ * this function validates, and if the syntax is valid, appends
+ * the user definition to a list for later loading.
+ *
+ * The rules are tested for validity and if there obvious syntax errors
+ * the function returns C_ERR and does nothing, otherwise C_OK is returned
+ * and the user is appended to the list.
+ *
+ * Note that this function cannot stop in case of commands that are not found
+ * and, in that case, the error will be emitted later, because certain
+ * commands may be defined later once modules are loaded.
+ *
+ * When an error is detected and C_ERR is returned, the function populates
+ * by reference (if not set to NULL) the argc_err argument with the index
+ * of the argv vector that caused the error. */
+int ACLAppendUserForLoading(sds *argv, int argc, int *argc_err) {
+    if (argc < 2 || strcasecmp(argv[0],"user")) {
+        if (argc_err) *argc_err = 0;
+        return C_ERR;
+    }
+
+    if (listSearchKey(UsersToLoad, argv[1])) {
+        if (argc_err) *argc_err = 1;
+        errno = EALREADY;
+        return C_ERR; 
+    }
+
+    /* Try to apply the user rules in a fake user to see if they
+     * are actually valid. */
+    user *fakeuser = ACLCreateUnlinkedUser();
+
+    /* Merged selectors before trying to process */
+    int merged_argc;
+    sds *acl_args = ACLMergeSelectorArguments(argv + 2, argc - 2, &merged_argc, argc_err);
+
+    if (!acl_args) {
+        return C_ERR;
+    }
+
+    for (int j = 0; j < merged_argc; j++) {
+        if (ACLSetUser(fakeuser,acl_args[j],sdslen(acl_args[j])) == C_ERR) {
+            if (errno != ENOENT) {
+                ACLFreeUser(fakeuser);
+                if (argc_err) *argc_err = j;
+                for (int i = 0; i < merged_argc; i++) sdsfree(acl_args[i]);
+                zfree(acl_args);
+                return C_ERR;
+            }
+        }
+    }
+
+    /* Rules look valid, let's append the user to the list. */
+    sds *copy = zmalloc(sizeof(sds)*(merged_argc + 2));
+    copy[0] = sdsdup(argv[1]);
+    for (int j = 0; j < merged_argc; j++) copy[j+1] = sdsdup(acl_args[j]);
+    copy[merged_argc + 1] = NULL;
+    listAddNodeTail(UsersToLoad,copy);
+    ACLFreeUser(fakeuser);
+    for (int i = 0; i < merged_argc; i++) sdsfree(acl_args[i]);
+    zfree(acl_args);
+    return C_OK;
+}
+
+/* This function will load the configured users appended to the server
+ * configuration via ACLAppendUserForLoading(). On loading errors it will
+ * log an error and return C_ERR, otherwise C_OK will be returned. */
+int ACLLoadConfiguredUsers(void) {
+    listIter li;
+    listNode *ln;
+    listRewind(UsersToLoad,&li);
+    while ((ln = listNext(&li)) != NULL) {
+        sds *aclrules = listNodeValue(ln);
+        sds username = aclrules[0];
+
+        if (ACLStringHasSpaces(aclrules[0],sdslen(aclrules[0]))) {
+            serverLog(LL_WARNING,"Spaces not allowed in ACL usernames");
+            return C_ERR;
+        }
+
+        user *u = ACLCreateUser(username,sdslen(username));
+        if (!u) {
+            /* Only valid duplicate user is the default one. */
+            serverAssert(!strcmp(username, "default"));
+            u = ACLGetUserByName("default",7);
+            ACLSetUser(u,"reset",-1);
+        }
+
+        /* Load every rule defined for this user. */
+        for (int j = 1; aclrules[j]; j++) {
+            if (ACLSetUser(u,aclrules[j],sdslen(aclrules[j])) != C_OK) {
+                const char *errmsg = ACLSetUserStringError();
+                serverLog(LL_WARNING,"Error loading ACL rule '%s' for "
+                                     "the user named '%s': %s",
+                          aclrules[j],aclrules[0],errmsg);
+                return C_ERR;
+            }
+        }
+
+        /* Having a disabled user in the configuration may be an error,
+         * warn about it without returning any error to the caller. */
+        if (u->flags & USER_FLAG_DISABLED) {
+            serverLog(LL_NOTICE, "The user '%s' is disabled (there is no "
+                                 "'on' modifier in the user description). Make "
+                                 "sure this is not a configuration error.",
+                      aclrules[0]);
+        }
+    }
+    return C_OK;
+}
+
+/* This function loads the ACL from the specified filename: every line
+ * is validated and should be either empty or in the format used to specify
+ * users in the redis.conf configuration or in the ACL file, that is:
+ *
+ *  user <username> ... rules ...
+ *
+ * Note that this function considers comments starting with '#' as errors
+ * because the ACL file is meant to be rewritten, and comments would be
+ * lost after the rewrite. Yet empty lines are allowed to avoid being too
+ * strict.
+ *
+ * One important part of implementing ACL LOAD, that uses this function, is
+ * to avoid ending with broken rules if the ACL file is invalid for some
+ * reason, so the function will attempt to validate the rules before loading
+ * each user. For every line that will be found broken the function will
+ * collect an error message.
+ *
+ * IMPORTANT: If there is at least a single error, nothing will be loaded
+ * and the rules will remain exactly as they were.
+ *
+ * At the end of the process, if no errors were found in the whole file then
+ * NULL is returned. Otherwise an SDS string describing in a single line
+ * a description of all the issues found is returned. */
+sds ACLLoadFromFile(const char *filename) {
+    FILE *fp;
+    char buf[1024];
+
+    /* Open the ACL file. */
+    if ((fp = fopen(filename,"r")) == NULL) {
+        sds errors = sdscatprintf(sdsempty(),
+            "Error loading ACLs, opening file '%s': %s",
+            filename, strerror(errno));
+        return errors;
+    }
+
+    /* Load the whole file as a single string in memory. */
+    sds acls = sdsempty();
+    while(fgets(buf,sizeof(buf),fp) != NULL)
+        acls = sdscat(acls,buf);
+    fclose(fp);
+
+    /* Split the file into lines and attempt to load each line. */
+    int totlines;
+    sds *lines, errors = sdsempty();
+    lines = sdssplitlen(acls,strlen(acls),"\n",1,&totlines);
+    sdsfree(acls);
+
+    /* We do all the loading in a fresh instance of the Users radix tree,
+     * so if there are errors loading the ACL file we can rollback to the
+     * old version. */
+    rax *old_users = Users;
+    Users = raxNew();
+
+    /* Load each line of the file. */
+    for (int i = 0; i < totlines; i++) {
+        sds *argv;
+        int argc;
+        int linenum = i+1;
+
+        lines[i] = sdstrim(lines[i]," \t\r\n");
+
+        /* Skip blank lines */
+        if (lines[i][0] == '\0') continue;
+
+        /* Split into arguments */
+        argv = sdssplitlen(lines[i],sdslen(lines[i])," ",1,&argc);
+        if (argv == NULL) {
+            errors = sdscatprintf(errors,
+                     "%s:%d: unbalanced quotes in acl line. ",
+                     server.acl_filename, linenum);
+            continue;
+        }
+
+        /* Skip this line if the resulting command vector is empty. */
+        if (argc == 0) {
+            sdsfreesplitres(argv,argc);
+            continue;
+        }
+
+        /* The line should start with the "user" keyword. */
+        if (strcmp(argv[0],"user") || argc < 2) {
+            errors = sdscatprintf(errors,
+                     "%s:%d should start with user keyword followed "
+                     "by the username. ", server.acl_filename,
+                     linenum);
+            sdsfreesplitres(argv,argc);
+            continue;
+        }
+
+        /* Spaces are not allowed in usernames. */
+        if (ACLStringHasSpaces(argv[1],sdslen(argv[1]))) {
+            errors = sdscatprintf(errors,
+                     "'%s:%d: username '%s' contains invalid characters. ",
+                     server.acl_filename, linenum, argv[1]);
+            sdsfreesplitres(argv,argc);
+            continue;
+        }
+
+        user *u = ACLCreateUser(argv[1],sdslen(argv[1]));
+
+        /* If the user already exists we assume it's an error and abort. */
+        if (!u) {
+            errors = sdscatprintf(errors,"WARNING: Duplicate user '%s' found on line %d. ", argv[1], linenum);
+            sdsfreesplitres(argv,argc);
+            continue;
+        }
+
+        /* Finally process the options and validate they can
+         * be cleanly applied to the user. If any option fails
+         * to apply, the other values won't be applied since
+         * all the pending changes will get dropped. */
+        int merged_argc;
+        sds *acl_args = ACLMergeSelectorArguments(argv + 2, argc - 2, &merged_argc, NULL);
+        if (!acl_args) {
+            errors = sdscatprintf(errors,
+                    "%s:%d: Unmatched parenthesis in selector definition.",
+                    server.acl_filename, linenum);
+        }
+
+        int syntax_error = 0;
+        for (int j = 0; j < merged_argc; j++) {
+            acl_args[j] = sdstrim(acl_args[j],"\t\r\n");
+            if (ACLSetUser(u,acl_args[j],sdslen(acl_args[j])) != C_OK) {
+                const char *errmsg = ACLSetUserStringError();
+                if (errno == ENOENT) {
+                    /* For missing commands, we print out more information since
+                     * it shouldn't contain any sensitive information. */
+                    errors = sdscatprintf(errors,
+                            "%s:%d: Error in applying operation '%s': %s. ",
+                            server.acl_filename, linenum, acl_args[j], errmsg);
+                } else if (syntax_error == 0) {
+                    /* For all other errors, only print out the first error encountered
+                     * since it might affect future operations. */
+                    errors = sdscatprintf(errors,
+                            "%s:%d: %s. ",
+                            server.acl_filename, linenum, errmsg);
+                    syntax_error = 1;
+                }
+            }
+        }
+
+        for (int i = 0; i < merged_argc; i++) sdsfree(acl_args[i]);
+        zfree(acl_args);
+
+        /* Apply the rule to the new users set only if so far there
+         * are no errors, otherwise it's useless since we are going
+         * to discard the new users set anyway. */
+        if (sdslen(errors) != 0) {
+            sdsfreesplitres(argv,argc);
+            continue;
+        }
+
+        sdsfreesplitres(argv,argc);
+    }
+
+    sdsfreesplitres(lines,totlines);
+
+    /* Check if we found errors and react accordingly. */
+    if (sdslen(errors) == 0) {
+        /* The default user pointer is referenced in different places: instead
+         * of replacing such occurrences it is much simpler to copy the new
+         * default user configuration in the old one. */
+        user *new_default = ACLGetUserByName("default",7);
+        if (!new_default) {
+            new_default = ACLCreateDefaultUser();
+        }
+
+        ACLCopyUser(DefaultUser,new_default);
+        ACLFreeUser(new_default);
+        raxInsert(Users,(unsigned char*)"default",7,DefaultUser,NULL);
+        raxRemove(old_users,(unsigned char*)"default",7,NULL);
+        ACLFreeUsersSet(old_users);
+        sdsfree(errors);
+        return NULL;
+    } else {
+        ACLFreeUsersSet(Users);
+        Users = old_users;
+        errors = sdscat(errors,"WARNING: ACL errors detected, no change to the previously active ACL rules was performed");
+        return errors;
+    }
+}
+
+/* Generate a copy of the ACLs currently in memory in the specified filename.
+ * Returns C_OK on success or C_ERR if there was an error during the I/O.
+ * When C_ERR is returned a log is produced with hints about the issue. */
+int ACLSaveToFile(const char *filename) {
+    sds acl = sdsempty();
+    int fd = -1;
+    sds tmpfilename = NULL;
+    int retval = C_ERR;
+
+    /* Let's generate an SDS string containing the new version of the
+     * ACL file. */
+    raxIterator ri;
+    raxStart(&ri,Users);
+    raxSeek(&ri,"^",NULL,0);
+    while(raxNext(&ri)) {
+        user *u = ri.data;
+        /* Return information in the configuration file format. */
+        sds user = sdsnew("user ");
+        user = sdscatsds(user,u->name);
+        user = sdscatlen(user," ",1);
+        robj *descr = ACLDescribeUser(u);
+        user = sdscatsds(user,descr->ptr);
+        decrRefCount(descr);
+        acl = sdscatsds(acl,user);
+        acl = sdscatlen(acl,"\n",1);
+        sdsfree(user);
+    }
+    raxStop(&ri);
+
+    /* Create a temp file with the new content. */
+    tmpfilename = sdsnew(filename);
+    tmpfilename = sdscatfmt(tmpfilename,".tmp-%i-%I",
+        (int)getpid(),(int)mstime());
+    if ((fd = open(tmpfilename,O_WRONLY|O_CREAT,0644)) == -1) {
+        serverLog(LL_WARNING,"Opening temp ACL file for ACL SAVE: %s",
+            strerror(errno));
+        goto cleanup;
+    }
+
+    /* Write it. */
+    if (write(fd,acl,sdslen(acl)) != (ssize_t)sdslen(acl)) {
+        serverLog(LL_WARNING,"Writing ACL file for ACL SAVE: %s",
+            strerror(errno));
+        goto cleanup;
+    }
+    close(fd); fd = -1;
+
+    /* Let's replace the new file with the old one. */
+    if (rename(tmpfilename,filename) == -1) {
+        serverLog(LL_WARNING,"Renaming ACL file for ACL SAVE: %s",
+            strerror(errno));
+        goto cleanup;
+    }
+    sdsfree(tmpfilename); tmpfilename = NULL;
+    retval = C_OK; /* If we reached this point, everything is fine. */
+
+cleanup:
+    if (fd != -1) close(fd);
+    if (tmpfilename) unlink(tmpfilename);
+    sdsfree(tmpfilename);
+    sdsfree(acl);
+    return retval;
+}
+
+/* This function is called once the server is already running, modules are
+ * loaded, and we are ready to start, in order to load the ACLs either from
+ * the pending list of users defined in redis.conf, or from the ACL file.
+ * The function will just exit with an error if the user is trying to mix
+ * both the loading methods. */
+void ACLLoadUsersAtStartup(void) {
+    if (server.acl_filename[0] != '\0' && listLength(UsersToLoad) != 0) {
+        serverLog(LL_WARNING,
+            "Configuring Redis with users defined in redis.conf and at "
+            "the same setting an ACL file path is invalid. This setup "
+            "is very likely to lead to configuration errors and security "
+            "holes, please define either an ACL file or declare users "
+            "directly in your redis.conf, but not both.");
+        exit(1);
+    }
+
+    if (ACLLoadConfiguredUsers() == C_ERR) {
+        serverLog(LL_WARNING,
+            "Critical error while loading ACLs. Exiting.");
+        exit(1);
+    }
+
+    if (server.acl_filename[0] != '\0') {
+        sds errors = ACLLoadFromFile(server.acl_filename);
+        if (errors) {
+            serverLog(LL_WARNING,
+                "Aborting Redis startup because of ACL errors: %s", errors);
+            sdsfree(errors);
+            exit(1);
+        }
+    }
+}
+
+/* =============================================================================
+ * ACL log
+ * ==========================================================================*/
+
+#define ACL_LOG_GROUPING_MAX_TIME_DELTA 60000
+
+/* This structure defines an entry inside the ACL log. */
+typedef struct ACLLogEntry {
+    uint64_t count;     /* Number of times this happened recently. */
+    int reason;         /* Reason for denying the command. ACL_DENIED_*. */
+    int context;        /* Toplevel, Lua or MULTI/EXEC? ACL_LOG_CTX_*. */
+    sds object;         /* The key name or command name. */
+    sds username;       /* User the client is authenticated with. */
+    mstime_t ctime;     /* Milliseconds time of last update to this entry. */
+    sds cinfo;          /* Client info (last client if updated). */
+} ACLLogEntry;
+
+/* This function will check if ACL entries 'a' and 'b' are similar enough
+ * that we should actually update the existing entry in our ACL log instead
+ * of creating a new one. */
+int ACLLogMatchEntry(ACLLogEntry *a, ACLLogEntry *b) {
+    if (a->reason != b->reason) return 0;
+    if (a->context != b->context) return 0;
+    mstime_t delta = a->ctime - b->ctime;
+    if (delta < 0) delta = -delta;
+    if (delta > ACL_LOG_GROUPING_MAX_TIME_DELTA) return 0;
+    if (sdscmp(a->object,b->object) != 0) return 0;
+    if (sdscmp(a->username,b->username) != 0) return 0;
+    return 1;
+}
+
+/* Release an ACL log entry. */
+void ACLFreeLogEntry(void *leptr) {
+    ACLLogEntry *le = leptr;
+    sdsfree(le->object);
+    sdsfree(le->username);
+    sdsfree(le->cinfo);
+    zfree(le);
+}
+
+/* Adds a new entry in the ACL log, making sure to delete the old entry
+ * if we reach the maximum length allowed for the log. This function attempts
+ * to find similar entries in the current log in order to bump the counter of
+ * the log entry instead of creating many entries for very similar ACL
+ * rules issues.
+ *
+ * The argpos argument is used when the reason is ACL_DENIED_KEY or 
+ * ACL_DENIED_CHANNEL, since it allows the function to log the key or channel
+ * name that caused the problem.
+ *
+ * The last 2 arguments are a manual override to be used, instead of any of the automatic
+ * ones which depend on the client and reason arguments (use NULL for default).
+ *
+ * If `object` is not NULL, this functions takes over it.
+ */
+void addACLLogEntry(client *c, int reason, int context, int argpos, sds username, sds object) {
+    /* Create a new entry. */
+    struct ACLLogEntry *le = zmalloc(sizeof(*le));
+    le->count = 1;
+    le->reason = reason;
+    le->username = sdsdup(username ? username : c->user->name);
+    le->ctime = mstime();
+
+    if (object) {
+        le->object = object;
+    } else {
+        switch(reason) {
+            case ACL_DENIED_CMD: le->object = sdsdup(c->cmd->fullname); break;
+            case ACL_DENIED_KEY: le->object = sdsdup(c->argv[argpos]->ptr); break;
+            case ACL_DENIED_CHANNEL: le->object = sdsdup(c->argv[argpos]->ptr); break;
+            case ACL_DENIED_AUTH: le->object = sdsdup(c->argv[0]->ptr); break;
+            default: le->object = sdsempty();
+        }
+    }
+
+    client *realclient = c;
+    if (realclient->flags & CLIENT_SCRIPT) realclient = server.script_caller;
+
+    le->cinfo = catClientInfoString(sdsempty(),realclient);
+    le->context = context;
+
+    /* Try to match this entry with past ones, to see if we can just
+     * update an existing entry instead of creating a new one. */
+    long toscan = 10; /* Do a limited work trying to find duplicated. */
+    listIter li;
+    listNode *ln;
+    listRewind(ACLLog,&li);
+    ACLLogEntry *match = NULL;
+    while (toscan-- && (ln = listNext(&li)) != NULL) {
+        ACLLogEntry *current = listNodeValue(ln);
+        if (ACLLogMatchEntry(current,le)) {
+            match = current;
+            listDelNode(ACLLog,ln);
+            listAddNodeHead(ACLLog,current);
+            break;
+        }
+    }
+
+    /* If there is a match update the entry, otherwise add it as a
+     * new one. */
+    if (match) {
+        /* We update a few fields of the existing entry and bump the
+         * counter of events for this entry. */
+        sdsfree(match->cinfo);
+        match->cinfo = le->cinfo;
+        match->ctime = le->ctime;
+        match->count++;
+
+        /* Release the old entry. */
+        le->cinfo = NULL;
+        ACLFreeLogEntry(le);
+    } else {
+        /* Add it to our list of entries. We'll have to trim the list
+         * to its maximum size. */
+        listAddNodeHead(ACLLog, le);
+        while(listLength(ACLLog) > server.acllog_max_len) {
+            listNode *ln = listLast(ACLLog);
+            ACLLogEntry *le = listNodeValue(ln);
+            ACLFreeLogEntry(le);
+            listDelNode(ACLLog,ln);
+        }
+    }
+}
+
+const char* getAclErrorMessage(int acl_res) {
+    /* Notice that a variant of this code also exists on aclCommand so
+     * it also need to be updated on changed. */
+    switch (acl_res) {
+    case ACL_DENIED_CMD:
+        return "can't run this command or subcommand";
+    case ACL_DENIED_KEY:
+        return "can't access at least one of the keys mentioned in the command arguments";
+    case ACL_DENIED_CHANNEL:
+        return "can't publish to the channel mentioned in the command";
+    default:
+        return "lacking the permissions for the command";
+    }
+    serverPanic("Reached deadcode on getAclErrorMessage");
+}
+
+/* =============================================================================
+ * ACL related commands
+ * ==========================================================================*/
+
+/* ACL CAT category */
+void aclCatWithFlags(client *c, dict *commands, uint64_t cflag, int *arraylen) {
+    dictEntry *de;
+    dictIterator *di = dictGetIterator(commands);
+
+    while ((de = dictNext(di)) != NULL) {
+        struct redisCommand *cmd = dictGetVal(de);
+        if (cmd->flags & CMD_MODULE) continue;
+        if (cmd->acl_categories & cflag) {
+            addReplyBulkCBuffer(c, cmd->fullname, sdslen(cmd->fullname));
+            (*arraylen)++;
+        }
+
+        if (cmd->subcommands_dict) {
+            aclCatWithFlags(c, cmd->subcommands_dict, cflag, arraylen);
+        }
+    }
+    dictReleaseIterator(di);
+}
+
+/* Add the formatted response from a single selector to the ACL GETUSER
+ * response. This function returns the number of fields added. 
+ * 
+ * Setting verbose to 1 means that the full qualifier for key and channel
+ * permissions are shown.
+ */
+int aclAddReplySelectorDescription(client *c, aclSelector *s) {
+    listIter li;
+    listNode *ln;
+
+    /* Commands */
+    addReplyBulkCString(c,"commands");
+    sds cmddescr = ACLDescribeSelectorCommandRules(s);
+    addReplyBulkSds(c,cmddescr);
+    
+    /* Key patterns */
+    addReplyBulkCString(c,"keys");
+    if (s->flags & SELECTOR_FLAG_ALLKEYS) {
+        addReplyBulkCBuffer(c,"~*",2);
+    } else {
+        sds dsl = sdsempty();
+        listRewind(s->patterns,&li);
+        while((ln = listNext(&li))) {
+            keyPattern *thispat = (keyPattern *) listNodeValue(ln);
+            if (ln != listFirst(s->patterns)) dsl = sdscat(dsl, " ");
+            dsl = sdsCatPatternString(dsl, thispat);
+        }
+        addReplyBulkSds(c, dsl);
+    }
+
+    /* Pub/sub patterns */
+    addReplyBulkCString(c,"channels");
+    if (s->flags & SELECTOR_FLAG_ALLCHANNELS) {
+        addReplyBulkCBuffer(c,"&*",2);
+    } else {
+        sds dsl = sdsempty();
+        listRewind(s->channels,&li);
+        while((ln = listNext(&li))) {
+            sds thispat = listNodeValue(ln);
+            if (ln != listFirst(s->channels)) dsl = sdscat(dsl, " ");
+            dsl = sdscatfmt(dsl, "&%S", thispat);
+        }
+        addReplyBulkSds(c, dsl);
+    }
+    return 3;
+}
+
+/* ACL -- show and modify the configuration of ACL users.
+ * ACL HELP
+ * ACL LOAD
+ * ACL SAVE
+ * ACL LIST
+ * ACL USERS
+ * ACL CAT [<category>]
+ * ACL SETUSER <username> ... acl rules ...
+ * ACL DELUSER <username> [...]
+ * ACL GETUSER <username>
+ * ACL GENPASS [<bits>]
+ * ACL WHOAMI
+ * ACL LOG [<count> | RESET]
+ */
+void aclCommand(client *c) {
+    char *sub = c->argv[1]->ptr;
+    if (!strcasecmp(sub,"setuser") && c->argc >= 3) {
+        /* Initially redact all of the arguments to not leak any information
+         * about the user. */
+        for (int j = 2; j < c->argc; j++) {
+            redactClientCommandArgument(c, j);
+        }
+
+        sds username = c->argv[2]->ptr;
+        /* Check username validity. */
+        if (ACLStringHasSpaces(username,sdslen(username))) {
+            addReplyErrorFormat(c,
+                "Usernames can't contain spaces or null characters");
+            return;
+        }
+
+        user *u = ACLGetUserByName(username,sdslen(username));
+
+        sds *temp_argv = zmalloc(c->argc * sizeof(sds));
+        for (int i = 3; i < c->argc; i++) temp_argv[i-3] = c->argv[i]->ptr;
+
+        sds error = ACLStringSetUser(u, username, temp_argv, c->argc - 3);
+        zfree(temp_argv);
+        if (error == NULL) {
+            addReply(c,shared.ok);
+        } else {
+            addReplyErrorSdsSafe(c, error);
+        }
+        return;
+    } else if (!strcasecmp(sub,"deluser") && c->argc >= 3) {
+        int deleted = 0;
+        for (int j = 2; j < c->argc; j++) {
+            sds username = c->argv[j]->ptr;
+            if (!strcmp(username,"default")) {
+                addReplyError(c,"The 'default' user cannot be removed");
+                return;
+            }
+        }
+
+        for (int j = 2; j < c->argc; j++) {
+            sds username = c->argv[j]->ptr;
+            user *u;
+            if (raxRemove(Users,(unsigned char*)username,
+                          sdslen(username),
+                          (void**)&u))
+            {
+                ACLFreeUserAndKillClients(u);
+                deleted++;
+            }
+        }
+        addReplyLongLong(c,deleted);
+    } else if (!strcasecmp(sub,"getuser") && c->argc == 3) {
+        user *u = ACLGetUserByName(c->argv[2]->ptr,sdslen(c->argv[2]->ptr));
+        if (u == NULL) {
+            addReplyNull(c);
+            return;
+        }
+
+        void *ufields = addReplyDeferredLen(c);
+        int fields = 3;
+
+        /* Flags */
+        addReplyBulkCString(c,"flags");
+        void *deflen = addReplyDeferredLen(c);
+        int numflags = 0;
+        for (int j = 0; ACLUserFlags[j].flag; j++) {
+            if (u->flags & ACLUserFlags[j].flag) {
+                addReplyBulkCString(c,ACLUserFlags[j].name);
+                numflags++;
+            }
+        }
+        setDeferredSetLen(c,deflen,numflags);
+
+        /* Passwords */
+        addReplyBulkCString(c,"passwords");
+        addReplyArrayLen(c,listLength(u->passwords));
+        listIter li;
+        listNode *ln;
+        listRewind(u->passwords,&li);
+        while((ln = listNext(&li))) {
+            sds thispass = listNodeValue(ln);
+            addReplyBulkCBuffer(c,thispass,sdslen(thispass));
+        }
+        /* Include the root selector at the top level for backwards compatibility */
+        fields += aclAddReplySelectorDescription(c, ACLUserGetRootSelector(u));
+
+        /* Describe all of the selectors on this user, including duplicating the root selector */
+        addReplyBulkCString(c,"selectors");
+        addReplyArrayLen(c, listLength(u->selectors) - 1);
+        listRewind(u->selectors,&li);
+        serverAssert(listNext(&li));
+        while((ln = listNext(&li))) {
+            void *slen = addReplyDeferredLen(c);
+            int sfields = aclAddReplySelectorDescription(c, (aclSelector *)listNodeValue(ln));
+            setDeferredMapLen(c, slen, sfields);
+        } 
+        setDeferredMapLen(c, ufields, fields);
+    } else if ((!strcasecmp(sub,"list") || !strcasecmp(sub,"users")) &&
+               c->argc == 2)
+    {
+        int justnames = !strcasecmp(sub,"users");
+        addReplyArrayLen(c,raxSize(Users));
+        raxIterator ri;
+        raxStart(&ri,Users);
+        raxSeek(&ri,"^",NULL,0);
+        while(raxNext(&ri)) {
+            user *u = ri.data;
+            if (justnames) {
+                addReplyBulkCBuffer(c,u->name,sdslen(u->name));
+            } else {
+                /* Return information in the configuration file format. */
+                sds config = sdsnew("user ");
+                config = sdscatsds(config,u->name);
+                config = sdscatlen(config," ",1);
+                robj *descr = ACLDescribeUser(u);
+                config = sdscatsds(config,descr->ptr);
+                decrRefCount(descr);
+                addReplyBulkSds(c,config);
+            }
+        }
+        raxStop(&ri);
+    } else if (!strcasecmp(sub,"whoami") && c->argc == 2) {
+        if (c->user != NULL) {
+            addReplyBulkCBuffer(c,c->user->name,sdslen(c->user->name));
+        } else {
+            addReplyNull(c);
+        }
+    } else if (server.acl_filename[0] == '\0' &&
+               (!strcasecmp(sub,"load") || !strcasecmp(sub,"save")))
+    {
+        addReplyError(c,"This Redis instance is not configured to use an ACL file. You may want to specify users via the ACL SETUSER command and then issue a CONFIG REWRITE (assuming you have a Redis configuration file set) in order to store users in the Redis configuration.");
+        return;
+    } else if (!strcasecmp(sub,"load") && c->argc == 2) {
+        sds errors = ACLLoadFromFile(server.acl_filename);
+        if (errors == NULL) {
+            addReply(c,shared.ok);
+        } else {
+            addReplyError(c,errors);
+            sdsfree(errors);
+        }
+    } else if (!strcasecmp(sub,"save") && c->argc == 2) {
+        if (ACLSaveToFile(server.acl_filename) == C_OK) {
+            addReply(c,shared.ok);
+        } else {
+            addReplyError(c,"There was an error trying to save the ACLs. "
+                            "Please check the server logs for more "
+                            "information");
+        }
+    } else if (!strcasecmp(sub,"cat") && c->argc == 2) {
+        void *dl = addReplyDeferredLen(c);
+        int j;
+        for (j = 0; ACLCommandCategories[j].flag != 0; j++)
+            addReplyBulkCString(c,ACLCommandCategories[j].name);
+        setDeferredArrayLen(c,dl,j);
+    } else if (!strcasecmp(sub,"cat") && c->argc == 3) {
+        uint64_t cflag = ACLGetCommandCategoryFlagByName(c->argv[2]->ptr);
+        if (cflag == 0) {
+            addReplyErrorFormat(c, "Unknown category '%.128s'", (char*)c->argv[2]->ptr);
+            return;
+        }
+        int arraylen = 0;
+        void *dl = addReplyDeferredLen(c);
+        aclCatWithFlags(c, server.orig_commands, cflag, &arraylen);
+        setDeferredArrayLen(c,dl,arraylen);
+    } else if (!strcasecmp(sub,"genpass") && (c->argc == 2 || c->argc == 3)) {
+        #define GENPASS_MAX_BITS 4096
+        char pass[GENPASS_MAX_BITS/8*2]; /* Hex representation. */
+        long bits = 256; /* By default generate 256 bits passwords. */
+
+        if (c->argc == 3 && getLongFromObjectOrReply(c,c->argv[2],&bits,NULL)
+            != C_OK) return;
+
+        if (bits <= 0 || bits > GENPASS_MAX_BITS) {
+            addReplyErrorFormat(c,
+                "ACL GENPASS argument must be the number of "
+                "bits for the output password, a positive number "
+                "up to %d",GENPASS_MAX_BITS);
+            return;
+        }
+
+        long chars = (bits+3)/4; /* Round to number of characters to emit. */
+        getRandomHexChars(pass,chars);
+        addReplyBulkCBuffer(c,pass,chars);
+    } else if (!strcasecmp(sub,"log") && (c->argc == 2 || c->argc ==3)) {
+        long count = 10; /* Number of entries to emit by default. */
+
+        /* Parse the only argument that LOG may have: it could be either
+         * the number of entries the user wants to display, or alternatively
+         * the "RESET" command in order to flush the old entries. */
+        if (c->argc == 3) {
+            if (!strcasecmp(c->argv[2]->ptr,"reset")) {
+                listSetFreeMethod(ACLLog,ACLFreeLogEntry);
+                listEmpty(ACLLog);
+                listSetFreeMethod(ACLLog,NULL);
+                addReply(c,shared.ok);
+                return;
+            } else if (getLongFromObjectOrReply(c,c->argv[2],&count,NULL)
+                       != C_OK)
+            {
+                return;
+            }
+            if (count < 0) count = 0;
+        }
+
+        /* Fix the count according to the number of entries we got. */
+        if ((size_t)count > listLength(ACLLog))
+            count = listLength(ACLLog);
+
+        addReplyArrayLen(c,count);
+        listIter li;
+        listNode *ln;
+        listRewind(ACLLog,&li);
+        mstime_t now = mstime();
+        while (count-- && (ln = listNext(&li)) != NULL) {
+            ACLLogEntry *le = listNodeValue(ln);
+            addReplyMapLen(c,7);
+            addReplyBulkCString(c,"count");
+            addReplyLongLong(c,le->count);
+
+            addReplyBulkCString(c,"reason");
+            char *reasonstr;
+            switch(le->reason) {
+            case ACL_DENIED_CMD: reasonstr="command"; break;
+            case ACL_DENIED_KEY: reasonstr="key"; break;
+            case ACL_DENIED_CHANNEL: reasonstr="channel"; break;
+            case ACL_DENIED_AUTH: reasonstr="auth"; break;
+            default: reasonstr="unknown";
+            }
+            addReplyBulkCString(c,reasonstr);
+
+            addReplyBulkCString(c,"context");
+            char *ctxstr;
+            switch(le->context) {
+            case ACL_LOG_CTX_TOPLEVEL: ctxstr="toplevel"; break;
+            case ACL_LOG_CTX_MULTI: ctxstr="multi"; break;
+            case ACL_LOG_CTX_LUA: ctxstr="lua"; break;
+            case ACL_LOG_CTX_MODULE: ctxstr="module"; break;
+            default: ctxstr="unknown";
+            }
+            addReplyBulkCString(c,ctxstr);
+
+            addReplyBulkCString(c,"object");
+            addReplyBulkCBuffer(c,le->object,sdslen(le->object));
+            addReplyBulkCString(c,"username");
+            addReplyBulkCBuffer(c,le->username,sdslen(le->username));
+            addReplyBulkCString(c,"age-seconds");
+            double age = (double)(now - le->ctime)/1000;
+            addReplyDouble(c,age);
+            addReplyBulkCString(c,"client-info");
+            addReplyBulkCBuffer(c,le->cinfo,sdslen(le->cinfo));
+        }
+    } else if (!strcasecmp(sub,"dryrun") && c->argc >= 4) {
+        struct redisCommand *cmd;
+        user *u = ACLGetUserByName(c->argv[2]->ptr,sdslen(c->argv[2]->ptr));
+        if (u == NULL) {
+            addReplyErrorFormat(c, "User '%s' not found", (char *)c->argv[2]->ptr);
+            return;
+        }
+
+        if ((cmd = lookupCommand(c->argv + 3, c->argc - 3)) == NULL) {
+            addReplyErrorFormat(c, "Command '%s' not found", (char *)c->argv[3]->ptr);
+            return;
+        }
+
+        if ((cmd->arity > 0 && cmd->arity != c->argc-3) ||
+            (c->argc-3 < -cmd->arity))
+        {
+            addReplyErrorFormat(c,"wrong number of arguments for '%s' command", cmd->fullname);
+            return;
+        }
+
+        int idx;
+        int result = ACLCheckAllUserCommandPerm(u, cmd, c->argv + 3, c->argc - 3, &idx);
+        /* Notice that a variant of this code also exists on getAclErrorMessage so
+         * it also need to be updated on changed. */
+        if (result != ACL_OK) {
+            sds err = sdsempty();
+            if (result == ACL_DENIED_CMD) {
+                err = sdscatfmt(err, "This user has no permissions to run "
+                    "the '%s' command", cmd->fullname);
+            } else if (result == ACL_DENIED_KEY) {
+                err = sdscatfmt(err, "This user has no permissions to access "
+                    "the '%s' key", c->argv[idx + 3]->ptr);
+            } else if (result == ACL_DENIED_CHANNEL) {
+                err = sdscatfmt(err, "This user has no permissions to access "
+                    "the '%s' channel", c->argv[idx + 3]->ptr);
+            } else {
+                serverPanic("Invalid permission result");
+            }
+            addReplyBulkSds(c, err);
+            return;
+        }
+
+        addReply(c,shared.ok);
+    } else if (c->argc == 2 && !strcasecmp(sub,"help")) {
+        const char *help[] = {
+"CAT [<category>]",
+"    List all commands that belong to <category>, or all command categories",
+"    when no category is specified.",
+"DELUSER <username> [<username> ...]",
+"    Delete a list of users.",
+"DRYRUN <username> <command> [<arg> ...]",
+"    Returns whether the user can execute the given command without executing the command.",
+"GETUSER <username>",
+"    Get the user's details.",
+"GENPASS [<bits>]",
+"    Generate a secure 256-bit user password. The optional `bits` argument can",
+"    be used to specify a different size.",
+"LIST",
+"    Show users details in config file format.",
+"LOAD",
+"    Reload users from the ACL file.",
+"LOG [<count> | RESET]",
+"    Show the ACL log entries.",
+"SAVE",
+"    Save the current config to the ACL file.",
+"SETUSER <username> <attribute> [<attribute> ...]",
+"    Create or modify a user with the specified attributes.",
+"USERS",
+"    List all the registered usernames.",
+"WHOAMI",
+"    Return the current connection username.",
+NULL
+        };
+        addReplyHelp(c,help);
+    } else {
+        addReplySubcommandSyntaxError(c);
+    }
+}
+
+void addReplyCommandCategories(client *c, struct redisCommand *cmd) {
+    int flagcount = 0;
+    void *flaglen = addReplyDeferredLen(c);
+    for (int j = 0; ACLCommandCategories[j].flag != 0; j++) {
+        if (cmd->acl_categories & ACLCommandCategories[j].flag) {
+            addReplyStatusFormat(c, "@%s", ACLCommandCategories[j].name);
+            flagcount++;
+        }
+    }
+    setDeferredSetLen(c, flaglen, flagcount);
+}
+
+/* AUTH <password>
+ * AUTH <username> <password> (Redis >= 6.0 form)
+ *
+ * When the user is omitted it means that we are trying to authenticate
+ * against the default user. */
+void authCommand(client *c) {
+    /* Only two or three argument forms are allowed. */
+    if (c->argc > 3) {
+        addReplyErrorObject(c,shared.syntaxerr);
+        return;
+    }
+    /* Always redact the second argument */
+    redactClientCommandArgument(c, 1);
+
+    /* Handle the two different forms here. The form with two arguments
+     * will just use "default" as username. */
+    robj *username, *password;
+    if (c->argc == 2) {
+        /* Mimic the old behavior of giving an error for the two argument
+         * form if no password is configured. */
+        if (DefaultUser->flags & USER_FLAG_NOPASS) {
+            addReplyError(c,"AUTH <password> called without any password "
+                            "configured for the default user. Are you sure "
+                            "your configuration is correct?");
+            return;
+        }
+
+        username = shared.default_username; 
+        password = c->argv[1];
+    } else {
+        username = c->argv[1];
+        password = c->argv[2];
+        redactClientCommandArgument(c, 2);
+    }
+
+    if (ACLAuthenticateUser(c,username,password) == C_OK) {
+        addReply(c,shared.ok);
+    } else {
+        addReplyError(c,"-WRONGPASS invalid username-password pair or user is disabled.");
+    }
+}
+
+/* Set the password for the "default" ACL user. This implements supports for
+ * requirepass config, so passing in NULL will set the user to be nopass. */
+void ACLUpdateDefaultUserPassword(sds password) {
+    ACLSetUser(DefaultUser,"resetpass",-1);
+    if (password) {
+        sds aclop = sdscatlen(sdsnew(">"), password, sdslen(password));
+        ACLSetUser(DefaultUser,aclop,sdslen(aclop));
+        sdsfree(aclop);
+    } else {
+        ACLSetUser(DefaultUser,"nopass",-1);
+    }
+}