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-rw-r--r--libmisc/find_new_uid.c483
1 files changed, 483 insertions, 0 deletions
diff --git a/libmisc/find_new_uid.c b/libmisc/find_new_uid.c
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+++ b/libmisc/find_new_uid.c
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+/*
+ * SPDX-FileCopyrightText: 1991 - 1994, Julianne Frances Haugh
+ * SPDX-FileCopyrightText: 2008 - 2011, Nicolas François
+ * SPDX-FileCopyrightText: 2014, Red Hat, Inc.
+ *
+ * SPDX-License-Identifier: BSD-3-Clause
+ */
+
+#include <config.h>
+
+#include <assert.h>
+#include <stdio.h>
+#include <errno.h>
+
+#include "prototypes.h"
+#include "pwio.h"
+#include "getdef.h"
+#include "shadowlog.h"
+
+/*
+ * get_ranges - Get the minimum and maximum ID ranges for the search
+ *
+ * This function will return the minimum and maximum ranges for IDs
+ *
+ * 0: The function completed successfully
+ * EINVAL: The provided ranges are impossible (such as maximum < minimum)
+ *
+ * preferred_min: The special-case minimum value for a specifically-
+ * requested ID, which may be lower than the standard min_id
+ */
+static int get_ranges (bool sys_user, uid_t *min_id, uid_t *max_id,
+ uid_t *preferred_min)
+{
+ uid_t uid_def_max = 0;
+
+ if (sys_user) {
+ /* System users */
+
+ /* A requested ID is allowed to be below the autoselect range */
+ *preferred_min = (uid_t) 1;
+
+ /* Get the minimum ID range from login.defs or default to 101 */
+ *min_id = (uid_t) getdef_ulong ("SYS_UID_MIN", 101UL);
+
+ /*
+ * If SYS_UID_MAX is unspecified, we should assume it to be one
+ * less than the UID_MIN (which is reserved for non-system accounts)
+ */
+ uid_def_max = (uid_t) getdef_ulong ("UID_MIN", 1000UL) - 1;
+ *max_id = (uid_t) getdef_ulong ("SYS_UID_MAX",
+ (unsigned long) uid_def_max);
+
+ /* Check that the ranges make sense */
+ if (*max_id < *min_id) {
+ (void) fprintf (log_get_logfd(),
+ _("%s: Invalid configuration: SYS_UID_MIN (%lu), "
+ "UID_MIN (%lu), SYS_UID_MAX (%lu)\n"),
+ log_get_progname(), (unsigned long) *min_id,
+ getdef_ulong ("UID_MIN", 1000UL),
+ (unsigned long) *max_id);
+ return EINVAL;
+ }
+ /*
+ * Zero is reserved for root and the allocation algorithm does not
+ * work right with it.
+ */
+ if (*min_id == 0) {
+ *min_id = (uid_t) 1;
+ }
+ } else {
+ /* Non-system users */
+
+ /* Get the values from login.defs or use reasonable defaults */
+ *min_id = (uid_t) getdef_ulong ("UID_MIN", 1000UL);
+ *max_id = (uid_t) getdef_ulong ("UID_MAX", 60000UL);
+
+ /*
+ * The preferred minimum should match the standard ID minimum
+ * for non-system users.
+ */
+ *preferred_min = *min_id;
+
+ /* Check that the ranges make sense */
+ if (*max_id < *min_id) {
+ (void) fprintf (log_get_logfd(),
+ _("%s: Invalid configuration: UID_MIN (%lu), "
+ "UID_MAX (%lu)\n"),
+ log_get_progname(), (unsigned long) *min_id,
+ (unsigned long) *max_id);
+ return EINVAL;
+ }
+ }
+
+ return 0;
+}
+
+/*
+ * check_uid - See if the requested UID is available
+ *
+ * On success, return 0
+ * If the ID is in use, return EEXIST
+ * If the ID is outside the range, return ERANGE
+ * In other cases, return errno from getpwuid()
+ */
+static int check_uid(const uid_t uid,
+ const uid_t uid_min,
+ const uid_t uid_max,
+ const bool *used_uids)
+{
+ /* First test that the preferred ID is in the range */
+ if (uid < uid_min || uid > uid_max) {
+ return ERANGE;
+ }
+
+ /*
+ * Check whether we already detected this UID
+ * using the pw_next() loop
+ */
+ if (used_uids != NULL && used_uids[uid]) {
+ return EEXIST;
+ }
+ /* Check if the UID exists according to NSS */
+ errno = 0;
+ if (prefix_getpwuid(uid) != NULL) {
+ return EEXIST;
+ } else {
+ /* getpwuid() was NULL
+ * we have to ignore errors as temporary
+ * failures of remote user identity services
+ * would completely block user/group creation
+ */
+ }
+
+ /* If we've made it here, the UID must be available */
+ return 0;
+}
+
+/*
+ * find_new_uid - Find a new unused UID.
+ *
+ * If successful, find_new_uid provides an unused user ID in the
+ * [UID_MIN:UID_MAX] range.
+ * This ID should be higher than all the used UID, but if not possible,
+ * the lowest unused ID in the range will be returned.
+ *
+ * Return 0 on success, -1 if no unused UIDs are available.
+ */
+int find_new_uid(bool sys_user,
+ uid_t *uid,
+ /*@null@*/uid_t const *preferred_uid)
+{
+ bool *used_uids;
+ const struct passwd *pwd;
+ uid_t uid_min, uid_max, preferred_min;
+ uid_t id;
+ uid_t lowest_found, highest_found;
+ int result;
+ int nospam = 0;
+
+ assert (uid != NULL);
+
+ /*
+ * First, figure out what ID range is appropriate for
+ * automatic assignment
+ */
+ result = get_ranges (sys_user, &uid_min, &uid_max, &preferred_min);
+ if (result == EINVAL) {
+ return -1;
+ }
+
+ /* Check if the preferred UID is available */
+ if (preferred_uid) {
+ result = check_uid (*preferred_uid, preferred_min, uid_max, NULL);
+ if (result == 0) {
+ /*
+ * Make sure the UID isn't queued for use already
+ */
+ if (pw_locate_uid (*preferred_uid) == NULL) {
+ *uid = *preferred_uid;
+ return 0;
+ }
+ /*
+ * pw_locate_uid() found the UID in an as-yet uncommitted
+ * entry. We'll proceed below and auto-set an UID.
+ */
+ } else if (result == EEXIST || result == ERANGE) {
+ /*
+ * Continue on below. At this time, we won't
+ * treat these two cases differently.
+ */
+ } else {
+ /*
+ * An unexpected error occurred. We should report
+ * this and fail the user creation.
+ * This differs from the automatic creation
+ * behavior below, since if a specific UID was
+ * requested and generated an error, the user is
+ * more likely to want to stop and address the
+ * issue.
+ */
+ fprintf (log_get_logfd(),
+ _("%s: Encountered error attempting to use "
+ "preferred UID: %s\n"),
+ log_get_progname(), strerror (result));
+ return -1;
+ }
+ }
+
+ /*
+ * Search the entire passwd file,
+ * looking for the next unused value.
+ *
+ * We first check the local database with pw_rewind/pw_next to find
+ * all local values that are in use.
+ *
+ * We then compare the next free value to all databases (local and
+ * remote) and iterate until we find a free one. If there are free
+ * values beyond the lowest (system users) or highest (non-system
+ * users), we will prefer those and avoid potentially reclaiming a
+ * deleted user (which can be a security issue, since it may grant
+ * access to files belonging to that former user).
+ *
+ * If there are no UIDs available at the end of the search, we will
+ * have no choice but to iterate through the range looking for gaps.
+ *
+ */
+
+ /* Create an array to hold all of the discovered UIDs */
+ used_uids = malloc (sizeof (bool) * (uid_max +1));
+ if (NULL == used_uids) {
+ fprintf (log_get_logfd(),
+ _("%s: failed to allocate memory: %s\n"),
+ log_get_progname(), strerror (errno));
+ return -1;
+ }
+ memset (used_uids, false, sizeof (bool) * (uid_max + 1));
+
+ /* First look for the lowest and highest value in the local database */
+ (void) pw_rewind ();
+ highest_found = uid_min;
+ lowest_found = uid_max;
+ while ((pwd = pw_next ()) != NULL) {
+ /*
+ * Does this entry have a lower UID than the lowest we've found
+ * so far?
+ */
+ if ((pwd->pw_uid <= lowest_found) && (pwd->pw_uid >= uid_min)) {
+ lowest_found = pwd->pw_uid - 1;
+ }
+
+ /*
+ * Does this entry have a higher UID than the highest we've found
+ * so far?
+ */
+ if ((pwd->pw_uid >= highest_found) && (pwd->pw_uid <= uid_max)) {
+ highest_found = pwd->pw_uid + 1;
+ }
+
+ /* create index of used UIDs */
+ if (pwd->pw_uid >= uid_min
+ && pwd->pw_uid <= uid_max) {
+
+ used_uids[pwd->pw_uid] = true;
+ }
+ }
+
+ if (sys_user) {
+ /*
+ * For system users, we want to start from the
+ * top of the range and work downwards.
+ */
+
+ /*
+ * At the conclusion of the pw_next() search, we will either
+ * have a presumed-free UID or we will be at UID_MIN - 1.
+ */
+ if (lowest_found < uid_min) {
+ /*
+ * In this case, an UID is in use at UID_MIN.
+ *
+ * We will reset the search to UID_MAX and proceed down
+ * through all the UIDs (skipping those we detected with
+ * used_uids) for a free one. It is a known issue that
+ * this may result in reusing a previously-deleted UID,
+ * so administrators should be instructed to use this
+ * auto-detection with care (and prefer to assign UIDs
+ * explicitly).
+ */
+ lowest_found = uid_max;
+ }
+
+ /* Search through all of the IDs in the range */
+ for (id = lowest_found; id >= uid_min; id--) {
+ result = check_uid (id, uid_min, uid_max, used_uids);
+ if (result == 0) {
+ /* This UID is available. Return it. */
+ *uid = id;
+ free (used_uids);
+ return 0;
+ } else if (result == EEXIST) {
+ /* This UID is in use, we'll continue to the next */
+ } else {
+ /*
+ * An unexpected error occurred.
+ *
+ * Only report it the first time to avoid spamming
+ * the logs
+ *
+ */
+ if (!nospam) {
+ fprintf (log_get_logfd(),
+ _("%s: Can't get unique system UID (%s). "
+ "Suppressing additional messages.\n"),
+ log_get_progname(), strerror (result));
+ SYSLOG ((LOG_ERR,
+ "Error checking available UIDs: %s",
+ strerror (result)));
+ nospam = 1;
+ }
+ /*
+ * We will continue anyway. Hopefully a later UID
+ * will work properly.
+ */
+ }
+ }
+
+ /*
+ * If we get all the way through the loop, try again from UID_MAX,
+ * unless that was where we previously started. (NOTE: the worst-case
+ * scenario here is that we will run through (UID_MAX - UID_MIN - 1)
+ * cycles *again* if we fall into this case with lowest_found as
+ * UID_MAX - 1, all users in the range in use and maintained by
+ * network services such as LDAP.)
+ */
+ if (lowest_found != uid_max) {
+ for (id = uid_max; id >= uid_min; id--) {
+ result = check_uid (id, uid_min, uid_max, used_uids);
+ if (result == 0) {
+ /* This UID is available. Return it. */
+ *uid = id;
+ free (used_uids);
+ return 0;
+ } else if (result == EEXIST) {
+ /* This UID is in use, we'll continue to the next */
+ } else {
+ /*
+ * An unexpected error occurred.
+ *
+ * Only report it the first time to avoid spamming
+ * the logs
+ *
+ */
+ if (!nospam) {
+ fprintf (log_get_logfd(),
+ _("%s: Can't get unique system UID (%s). "
+ "Suppressing additional messages.\n"),
+ log_get_progname(), strerror (result));
+ SYSLOG((LOG_ERR,
+ "Error checking available UIDs: %s",
+ strerror (result)));
+ nospam = 1;
+ }
+ /*
+ * We will continue anyway. Hopefully a later UID
+ * will work properly.
+ */
+ }
+ }
+ }
+ } else { /* !sys_user */
+ /*
+ * For non-system users, we want to start from the
+ * bottom of the range and work upwards.
+ */
+
+ /*
+ * At the conclusion of the pw_next() search, we will either
+ * have a presumed-free UID or we will be at UID_MAX + 1.
+ */
+ if (highest_found > uid_max) {
+ /*
+ * In this case, a UID is in use at UID_MAX.
+ *
+ * We will reset the search to UID_MIN and proceed up
+ * through all the UIDs (skipping those we detected with
+ * used_uids) for a free one. It is a known issue that
+ * this may result in reusing a previously-deleted UID,
+ * so administrators should be instructed to use this
+ * auto-detection with care (and prefer to assign UIDs
+ * explicitly).
+ */
+ highest_found = uid_min;
+ }
+
+ /* Search through all of the IDs in the range */
+ for (id = highest_found; id <= uid_max; id++) {
+ result = check_uid (id, uid_min, uid_max, used_uids);
+ if (result == 0) {
+ /* This UID is available. Return it. */
+ *uid = id;
+ free (used_uids);
+ return 0;
+ } else if (result == EEXIST) {
+ /* This UID is in use, we'll continue to the next */
+ } else {
+ /*
+ * An unexpected error occurred.
+ *
+ * Only report it the first time to avoid spamming
+ * the logs
+ *
+ */
+ if (!nospam) {
+ fprintf (log_get_logfd(),
+ _("%s: Can't get unique UID (%s). "
+ "Suppressing additional messages.\n"),
+ log_get_progname(), strerror (result));
+ SYSLOG ((LOG_ERR,
+ "Error checking available UIDs: %s",
+ strerror (result)));
+ nospam = 1;
+ }
+ /*
+ * We will continue anyway. Hopefully a later UID
+ * will work properly.
+ */
+ }
+ }
+
+ /*
+ * If we get all the way through the loop, try again from UID_MIN,
+ * unless that was where we previously started. (NOTE: the worst-case
+ * scenario here is that we will run through (UID_MAX - UID_MIN - 1)
+ * cycles *again* if we fall into this case with highest_found as
+ * UID_MIN + 1, all users in the range in use and maintained by
+ * network services such as LDAP.)
+ */
+ if (highest_found != uid_min) {
+ for (id = uid_min; id <= uid_max; id++) {
+ result = check_uid (id, uid_min, uid_max, used_uids);
+ if (result == 0) {
+ /* This UID is available. Return it. */
+ *uid = id;
+ free (used_uids);
+ return 0;
+ } else if (result == EEXIST) {
+ /* This UID is in use, we'll continue to the next */
+ } else {
+ /*
+ * An unexpected error occurred.
+ *
+ * Only report it the first time to avoid spamming
+ * the logs
+ *
+ */
+ if (!nospam) {
+ fprintf (log_get_logfd(),
+ _("%s: Can't get unique UID (%s). "
+ "Suppressing additional messages.\n"),
+ log_get_progname(), strerror (result));
+ SYSLOG ((LOG_ERR,
+ "Error checking available UIDs: %s",
+ strerror (result)));
+ nospam = 1;
+ }
+ /*
+ * We will continue anyway. Hopefully a later UID
+ * will work properly.
+ */
+ }
+ }
+ }
+ }
+
+ /* The code reached here and found no available IDs in the range */
+ fprintf (log_get_logfd(),
+ _("%s: Can't get unique UID (no more available UIDs)\n"),
+ log_get_progname());
+ SYSLOG ((LOG_WARN, "no more available UIDs on the system"));
+ free (used_uids);
+ return -1;
+}
+
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