diff options
Diffstat (limited to 'net/dns_resolver')
| -rw-r--r-- | net/dns_resolver/Kconfig | 27 | ||||
| -rw-r--r-- | net/dns_resolver/Makefile | 7 | ||||
| -rw-r--r-- | net/dns_resolver/dns_key.c | 322 | ||||
| -rw-r--r-- | net/dns_resolver/dns_query.c | 170 | ||||
| -rw-r--r-- | net/dns_resolver/internal.h | 51 |
5 files changed, 577 insertions, 0 deletions
diff --git a/net/dns_resolver/Kconfig b/net/dns_resolver/Kconfig new file mode 100644 index 000000000..50d49f7e0 --- /dev/null +++ b/net/dns_resolver/Kconfig @@ -0,0 +1,27 @@ +# +# Configuration for DNS Resolver +# +config DNS_RESOLVER + tristate "DNS Resolver support" + depends on NET && KEYS + help + Saying Y here will include support for the DNS Resolver key type + which can be used to make upcalls to perform DNS lookups in + userspace. + + DNS Resolver is used to query DNS server for information. Examples + being resolving a UNC hostname element to an IP address for CIFS or + performing a DNS query for AFSDB records so that AFS can locate a + cell's volume location database servers. + + DNS Resolver is used by the CIFS and AFS modules, and would support + SMB2 later. DNS Resolver is supported by the userspace upcall + helper "/sbin/dns.resolver" via /etc/request-key.conf. + + See <file:Documentation/networking/dns_resolver.txt> for further + information. + + To compile this as a module, choose M here: the module will be called + dnsresolver. + + If unsure, say N. diff --git a/net/dns_resolver/Makefile b/net/dns_resolver/Makefile new file mode 100644 index 000000000..d5c13c2eb --- /dev/null +++ b/net/dns_resolver/Makefile @@ -0,0 +1,7 @@ +# +# Makefile for the Linux DNS Resolver. +# + +obj-$(CONFIG_DNS_RESOLVER) += dns_resolver.o + +dns_resolver-y := dns_key.o dns_query.o diff --git a/net/dns_resolver/dns_key.c b/net/dns_resolver/dns_key.c new file mode 100644 index 000000000..a0494206c --- /dev/null +++ b/net/dns_resolver/dns_key.c @@ -0,0 +1,322 @@ +/* Key type used to cache DNS lookups made by the kernel + * + * See Documentation/networking/dns_resolver.txt + * + * Copyright (c) 2007 Igor Mammedov + * Author(s): Igor Mammedov (niallain@gmail.com) + * Steve French (sfrench@us.ibm.com) + * Wang Lei (wang840925@gmail.com) + * David Howells (dhowells@redhat.com) + * + * This library is free software; you can redistribute it and/or modify + * it under the terms of the GNU Lesser General Public License as published + * by the Free Software Foundation; either version 2.1 of the License, or + * (at your option) any later version. + * + * This library is distributed in the hope that it will be useful, + * but WITHOUT ANY WARRANTY; without even the implied warranty of + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See + * the GNU Lesser General Public License for more details. + * + * You should have received a copy of the GNU Lesser General Public License + * along with this library; if not, see <http://www.gnu.org/licenses/>. + */ +#include <linux/module.h> +#include <linux/moduleparam.h> +#include <linux/slab.h> +#include <linux/string.h> +#include <linux/kernel.h> +#include <linux/keyctl.h> +#include <linux/err.h> +#include <linux/seq_file.h> +#include <keys/dns_resolver-type.h> +#include <keys/user-type.h> +#include "internal.h" + +MODULE_DESCRIPTION("DNS Resolver"); +MODULE_AUTHOR("Wang Lei"); +MODULE_LICENSE("GPL"); + +unsigned int dns_resolver_debug; +module_param_named(debug, dns_resolver_debug, uint, 0644); +MODULE_PARM_DESC(debug, "DNS Resolver debugging mask"); + +const struct cred *dns_resolver_cache; + +#define DNS_ERRORNO_OPTION "dnserror" + +/* + * Preparse instantiation data for a dns_resolver key. + * + * The data must be a NUL-terminated string, with the NUL char accounted in + * datalen. + * + * If the data contains a '#' characters, then we take the clause after each + * one to be an option of the form 'key=value'. The actual data of interest is + * the string leading up to the first '#'. For instance: + * + * "ip1,ip2,...#foo=bar" + */ +static int +dns_resolver_preparse(struct key_preparsed_payload *prep) +{ + struct user_key_payload *upayload; + unsigned long derrno; + int ret; + int datalen = prep->datalen, result_len = 0; + const char *data = prep->data, *end, *opt; + + kenter("'%*.*s',%u", datalen, datalen, data, datalen); + + if (datalen <= 1 || !data || data[datalen - 1] != '\0') + return -EINVAL; + datalen--; + + /* deal with any options embedded in the data */ + end = data + datalen; + opt = memchr(data, '#', datalen); + if (!opt) { + /* no options: the entire data is the result */ + kdebug("no options"); + result_len = datalen; + } else { + const char *next_opt; + + result_len = opt - data; + opt++; + kdebug("options: '%s'", opt); + do { + int opt_len, opt_nlen; + const char *eq; + char optval[128]; + + next_opt = memchr(opt, '#', end - opt) ?: end; + opt_len = next_opt - opt; + if (opt_len <= 0 || opt_len > sizeof(optval)) { + pr_warn_ratelimited("Invalid option length (%d) for dns_resolver key\n", + opt_len); + return -EINVAL; + } + + eq = memchr(opt, '=', opt_len); + if (eq) { + opt_nlen = eq - opt; + eq++; + memcpy(optval, eq, next_opt - eq); + optval[next_opt - eq] = '\0'; + } else { + opt_nlen = opt_len; + optval[0] = '\0'; + } + + kdebug("option '%*.*s' val '%s'", + opt_nlen, opt_nlen, opt, optval); + + /* see if it's an error number representing a DNS error + * that's to be recorded as the result in this key */ + if (opt_nlen == sizeof(DNS_ERRORNO_OPTION) - 1 && + memcmp(opt, DNS_ERRORNO_OPTION, opt_nlen) == 0) { + kdebug("dns error number option"); + + ret = kstrtoul(optval, 10, &derrno); + if (ret < 0) + goto bad_option_value; + + if (derrno < 1 || derrno > 511) + goto bad_option_value; + + kdebug("dns error no. = %lu", derrno); + prep->payload.data[dns_key_error] = ERR_PTR(-derrno); + continue; + } + + bad_option_value: + pr_warn_ratelimited("Option '%*.*s' to dns_resolver key: bad/missing value\n", + opt_nlen, opt_nlen, opt); + return -EINVAL; + } while (opt = next_opt + 1, opt < end); + } + + /* don't cache the result if we're caching an error saying there's no + * result */ + if (prep->payload.data[dns_key_error]) { + kleave(" = 0 [h_error %ld]", PTR_ERR(prep->payload.data[dns_key_error])); + return 0; + } + + kdebug("store result"); + prep->quotalen = result_len; + + upayload = kmalloc(sizeof(*upayload) + result_len + 1, GFP_KERNEL); + if (!upayload) { + kleave(" = -ENOMEM"); + return -ENOMEM; + } + + upayload->datalen = result_len; + memcpy(upayload->data, data, result_len); + upayload->data[result_len] = '\0'; + + prep->payload.data[dns_key_data] = upayload; + kleave(" = 0"); + return 0; +} + +/* + * Clean up the preparse data + */ +static void dns_resolver_free_preparse(struct key_preparsed_payload *prep) +{ + pr_devel("==>%s()\n", __func__); + + kfree(prep->payload.data[dns_key_data]); +} + +/* + * The description is of the form "[<type>:]<domain_name>" + * + * The domain name may be a simple name or an absolute domain name (which + * should end with a period). The domain name is case-independent. + */ +static bool dns_resolver_cmp(const struct key *key, + const struct key_match_data *match_data) +{ + int slen, dlen, ret = 0; + const char *src = key->description, *dsp = match_data->raw_data; + + kenter("%s,%s", src, dsp); + + if (!src || !dsp) + goto no_match; + + if (strcasecmp(src, dsp) == 0) + goto matched; + + slen = strlen(src); + dlen = strlen(dsp); + if (slen <= 0 || dlen <= 0) + goto no_match; + if (src[slen - 1] == '.') + slen--; + if (dsp[dlen - 1] == '.') + dlen--; + if (slen != dlen || strncasecmp(src, dsp, slen) != 0) + goto no_match; + +matched: + ret = 1; +no_match: + kleave(" = %d", ret); + return ret; +} + +/* + * Preparse the match criterion. + */ +static int dns_resolver_match_preparse(struct key_match_data *match_data) +{ + match_data->lookup_type = KEYRING_SEARCH_LOOKUP_ITERATE; + match_data->cmp = dns_resolver_cmp; + return 0; +} + +/* + * Describe a DNS key + */ +static void dns_resolver_describe(const struct key *key, struct seq_file *m) +{ + seq_puts(m, key->description); + if (key_is_positive(key)) { + int err = PTR_ERR(key->payload.data[dns_key_error]); + + if (err) + seq_printf(m, ": %d", err); + else + seq_printf(m, ": %u", key->datalen); + } +} + +/* + * read the DNS data + * - the key's semaphore is read-locked + */ +static long dns_resolver_read(const struct key *key, + char *buffer, size_t buflen) +{ + int err = PTR_ERR(key->payload.data[dns_key_error]); + + if (err) + return err; + + return user_read(key, buffer, buflen); +} + +struct key_type key_type_dns_resolver = { + .name = "dns_resolver", + .preparse = dns_resolver_preparse, + .free_preparse = dns_resolver_free_preparse, + .instantiate = generic_key_instantiate, + .match_preparse = dns_resolver_match_preparse, + .revoke = user_revoke, + .destroy = user_destroy, + .describe = dns_resolver_describe, + .read = dns_resolver_read, +}; + +static int __init init_dns_resolver(void) +{ + struct cred *cred; + struct key *keyring; + int ret; + + /* create an override credential set with a special thread keyring in + * which DNS requests are cached + * + * this is used to prevent malicious redirections from being installed + * with add_key(). + */ + cred = prepare_kernel_cred(NULL); + if (!cred) + return -ENOMEM; + + keyring = keyring_alloc(".dns_resolver", + GLOBAL_ROOT_UID, GLOBAL_ROOT_GID, cred, + (KEY_POS_ALL & ~KEY_POS_SETATTR) | + KEY_USR_VIEW | KEY_USR_READ, + KEY_ALLOC_NOT_IN_QUOTA, NULL, NULL); + if (IS_ERR(keyring)) { + ret = PTR_ERR(keyring); + goto failed_put_cred; + } + + ret = register_key_type(&key_type_dns_resolver); + if (ret < 0) + goto failed_put_key; + + /* instruct request_key() to use this special keyring as a cache for + * the results it looks up */ + set_bit(KEY_FLAG_ROOT_CAN_CLEAR, &keyring->flags); + cred->thread_keyring = keyring; + cred->jit_keyring = KEY_REQKEY_DEFL_THREAD_KEYRING; + dns_resolver_cache = cred; + + kdebug("DNS resolver keyring: %d\n", key_serial(keyring)); + return 0; + +failed_put_key: + key_put(keyring); +failed_put_cred: + put_cred(cred); + return ret; +} + +static void __exit exit_dns_resolver(void) +{ + key_revoke(dns_resolver_cache->thread_keyring); + unregister_key_type(&key_type_dns_resolver); + put_cred(dns_resolver_cache); +} + +module_init(init_dns_resolver) +module_exit(exit_dns_resolver) +MODULE_LICENSE("GPL"); diff --git a/net/dns_resolver/dns_query.c b/net/dns_resolver/dns_query.c new file mode 100644 index 000000000..49da67034 --- /dev/null +++ b/net/dns_resolver/dns_query.c @@ -0,0 +1,170 @@ +/* Upcall routine, designed to work as a key type and working through + * /sbin/request-key to contact userspace when handling DNS queries. + * + * See Documentation/networking/dns_resolver.txt + * + * Copyright (c) 2007 Igor Mammedov + * Author(s): Igor Mammedov (niallain@gmail.com) + * Steve French (sfrench@us.ibm.com) + * Wang Lei (wang840925@gmail.com) + * David Howells (dhowells@redhat.com) + * + * The upcall wrapper used to make an arbitrary DNS query. + * + * This function requires the appropriate userspace tool dns.upcall to be + * installed and something like the following lines should be added to the + * /etc/request-key.conf file: + * + * create dns_resolver * * /sbin/dns.upcall %k + * + * For example to use this module to query AFSDB RR: + * + * create dns_resolver afsdb:* * /sbin/dns.afsdb %k + * + * This library is free software; you can redistribute it and/or modify + * it under the terms of the GNU Lesser General Public License as published + * by the Free Software Foundation; either version 2.1 of the License, or + * (at your option) any later version. + * + * This library is distributed in the hope that it will be useful, + * but WITHOUT ANY WARRANTY; without even the implied warranty of + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See + * the GNU Lesser General Public License for more details. + * + * You should have received a copy of the GNU Lesser General Public License + * along with this library; if not, see <http://www.gnu.org/licenses/>. + */ + +#include <linux/module.h> +#include <linux/slab.h> +#include <linux/cred.h> +#include <linux/dns_resolver.h> +#include <linux/err.h> + +#include <keys/dns_resolver-type.h> +#include <keys/user-type.h> + +#include "internal.h" + +/** + * dns_query - Query the DNS + * @type: Query type (or NULL for straight host->IP lookup) + * @name: Name to look up + * @namelen: Length of name + * @options: Request options (or NULL if no options) + * @_result: Where to place the returned data (or NULL) + * @_expiry: Where to store the result expiry time (or NULL) + * + * The data will be returned in the pointer at *result, if provided, and the + * caller is responsible for freeing it. + * + * The description should be of the form "[<query_type>:]<domain_name>", and + * the options need to be appropriate for the query type requested. If no + * query_type is given, then the query is a straight hostname to IP address + * lookup. + * + * The DNS resolution lookup is performed by upcalling to userspace by way of + * requesting a key of type dns_resolver. + * + * Returns the size of the result on success, -ve error code otherwise. + */ +int dns_query(const char *type, const char *name, size_t namelen, + const char *options, char **_result, time64_t *_expiry) +{ + struct key *rkey; + struct user_key_payload *upayload; + const struct cred *saved_cred; + size_t typelen, desclen; + char *desc, *cp; + int ret, len; + + kenter("%s,%*.*s,%zu,%s", + type, (int)namelen, (int)namelen, name, namelen, options); + + if (!name || namelen == 0) + return -EINVAL; + + /* construct the query key description as "[<type>:]<name>" */ + typelen = 0; + desclen = 0; + if (type) { + typelen = strlen(type); + if (typelen < 1) + return -EINVAL; + desclen += typelen + 1; + } + + if (!namelen) + namelen = strnlen(name, 256); + if (namelen < 3 || namelen > 255) + return -EINVAL; + desclen += namelen + 1; + + desc = kmalloc(desclen, GFP_KERNEL); + if (!desc) + return -ENOMEM; + + cp = desc; + if (type) { + memcpy(cp, type, typelen); + cp += typelen; + *cp++ = ':'; + } + memcpy(cp, name, namelen); + cp += namelen; + *cp = '\0'; + + if (!options) + options = ""; + kdebug("call request_key(,%s,%s)", desc, options); + + /* make the upcall, using special credentials to prevent the use of + * add_key() to preinstall malicious redirections + */ + saved_cred = override_creds(dns_resolver_cache); + rkey = request_key(&key_type_dns_resolver, desc, options); + revert_creds(saved_cred); + kfree(desc); + if (IS_ERR(rkey)) { + ret = PTR_ERR(rkey); + goto out; + } + + down_read(&rkey->sem); + set_bit(KEY_FLAG_ROOT_CAN_INVAL, &rkey->flags); + rkey->perm |= KEY_USR_VIEW; + + ret = key_validate(rkey); + if (ret < 0) + goto put; + + /* If the DNS server gave an error, return that to the caller */ + ret = PTR_ERR(rkey->payload.data[dns_key_error]); + if (ret) + goto put; + + upayload = user_key_payload_locked(rkey); + len = upayload->datalen; + + if (_result) { + ret = -ENOMEM; + *_result = kmalloc(len + 1, GFP_KERNEL); + if (!*_result) + goto put; + + memcpy(*_result, upayload->data, len); + (*_result)[len] = '\0'; + } + + if (_expiry) + *_expiry = rkey->expiry; + + ret = len; +put: + up_read(&rkey->sem); + key_put(rkey); +out: + kleave(" = %d", ret); + return ret; +} +EXPORT_SYMBOL(dns_query); diff --git a/net/dns_resolver/internal.h b/net/dns_resolver/internal.h new file mode 100644 index 000000000..0c570d40e --- /dev/null +++ b/net/dns_resolver/internal.h @@ -0,0 +1,51 @@ +/* + * Copyright (c) 2010 Wang Lei + * Author(s): Wang Lei (wang840925@gmail.com). All Rights Reserved. + * + * Internal DNS Rsolver stuff + * + * This library is free software; you can redistribute it and/or modify + * it under the terms of the GNU Lesser General Public License as published + * by the Free Software Foundation; either version 2.1 of the License, or + * (at your option) any later version. + * + * This library is distributed in the hope that it will be useful, + * but WITHOUT ANY WARRANTY; without even the implied warranty of + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See + * the GNU Lesser General Public License for more details. + * + * You should have received a copy of the GNU Lesser General Public License + * along with this library; if not, see <http://www.gnu.org/licenses/>. + */ + +#include <linux/compiler.h> +#include <linux/kernel.h> +#include <linux/sched.h> + +/* + * Layout of key payload words. + */ +enum { + dns_key_data, + dns_key_error, +}; + +/* + * dns_key.c + */ +extern const struct cred *dns_resolver_cache; + +/* + * debug tracing + */ +extern unsigned int dns_resolver_debug; + +#define kdebug(FMT, ...) \ +do { \ + if (unlikely(dns_resolver_debug)) \ + printk(KERN_DEBUG "[%-6.6s] "FMT"\n", \ + current->comm, ##__VA_ARGS__); \ +} while (0) + +#define kenter(FMT, ...) kdebug("==> %s("FMT")", __func__, ##__VA_ARGS__) +#define kleave(FMT, ...) kdebug("<== %s()"FMT"", __func__, ##__VA_ARGS__) |