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-rw-r--r--lib/find_new_gid.c500
1 files changed, 500 insertions, 0 deletions
diff --git a/lib/find_new_gid.c b/lib/find_new_gid.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 "alloc.h"
+#include "prototypes.h"
+#include "groupio.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_group, gid_t *min_id, gid_t *max_id,
+ gid_t *preferred_min)
+{
+ gid_t gid_def_max = 0;
+
+ if (sys_group) {
+ /* System groups */
+
+ /* A requested ID is allowed to be below the autoselect range */
+ *preferred_min = (gid_t) 1;
+
+ /* Get the minimum ID range from login.defs or default to 101 */
+ *min_id = getdef_ulong ("SYS_GID_MIN", 101UL);
+
+ /*
+ * If SYS_GID_MAX is unspecified, we should assume it to be one
+ * less than the GID_MIN (which is reserved for non-system accounts)
+ */
+ gid_def_max = getdef_ulong ("GID_MIN", 1000UL) - 1;
+ *max_id = getdef_ulong ("SYS_GID_MAX", gid_def_max);
+
+ /* Check that the ranges make sense */
+ if (*max_id < *min_id) {
+ (void) fprintf (log_get_logfd(),
+ _("%s: Invalid configuration: SYS_GID_MIN (%lu), "
+ "GID_MIN (%lu), SYS_GID_MAX (%lu)\n"),
+ log_get_progname(), (unsigned long) *min_id,
+ getdef_ulong ("GID_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 = (gid_t) 1;
+ }
+ } else {
+ /* Non-system groups */
+
+ /* Get the values from login.defs or use reasonable defaults */
+ *min_id = getdef_ulong ("GID_MIN", 1000UL);
+ *max_id = getdef_ulong ("GID_MAX", 60000UL);
+
+ /*
+ * The preferred minimum should match the standard ID minimum
+ * for non-system groups.
+ */
+ *preferred_min = *min_id;
+
+ /* Check that the ranges make sense */
+ if (*max_id < *min_id) {
+ (void) fprintf (log_get_logfd(),
+ _("%s: Invalid configuration: GID_MIN (%lu), "
+ "GID_MAX (%lu)\n"),
+ log_get_progname(), (unsigned long) *min_id,
+ (unsigned long) *max_id);
+ return EINVAL;
+ }
+ }
+
+ return 0;
+}
+
+/*
+ * check_gid - See if the requested GID is available
+ *
+ * On success, return 0
+ * If the ID is in use, return EEXIST
+ * If the ID might clash with -1, return EINVAL
+ * If the ID is outside the range, return ERANGE
+ * In other cases, return errno from getgrgid()
+ */
+static int check_gid (const gid_t gid,
+ const gid_t gid_min,
+ const gid_t gid_max,
+ const bool *used_gids)
+{
+ /* First test that the preferred ID is in the range */
+ if (gid < gid_min || gid > gid_max) {
+ return ERANGE;
+ }
+
+ /* Check for compatibility with 16b and 32b gid_t error codes */
+ if (gid == UINT16_MAX || gid == UINT32_MAX) {
+ return EINVAL;
+ }
+
+ /*
+ * Check whether we already detected this GID
+ * using the gr_next() loop
+ */
+ if (used_gids != NULL && used_gids[gid]) {
+ return EEXIST;
+ }
+ /* Check if the GID exists according to NSS */
+ errno = 0;
+ if (prefix_getgrgid (gid) != NULL) {
+ return EEXIST;
+ } else {
+ /* getgrgid() 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 GID must be available */
+ return 0;
+}
+
+/*
+ * find_new_gid - Find a new unused GID.
+ *
+ * If successful, find_new_gid provides an unused group ID in the
+ * [GID_MIN:GID_MAX] range.
+ * This ID should be higher than all the used GID, but if not possible,
+ * the lowest unused ID in the range will be returned.
+ *
+ * Return 0 on success, -1 if no unused GIDs are available.
+ */
+int find_new_gid (bool sys_group,
+ gid_t *gid,
+ /*@null@*/gid_t const *preferred_gid)
+{
+ bool *used_gids;
+ const struct group *grp;
+ gid_t gid_min, gid_max, preferred_min;
+ gid_t id;
+ gid_t lowest_found, highest_found;
+ int result;
+ int nospam = 0;
+
+ assert(gid != NULL);
+
+ /*
+ * First, figure out what ID range is appropriate for
+ * automatic assignment
+ */
+ result = get_ranges (sys_group, &gid_min, &gid_max, &preferred_min);
+ if (result == EINVAL) {
+ return -1;
+ }
+
+ /* Check if the preferred GID is available */
+ if (preferred_gid) {
+ result = check_gid (*preferred_gid, preferred_min, gid_max, NULL);
+ if (result == 0) {
+ /*
+ * Make sure the GID isn't queued for use already
+ */
+ if (gr_locate_gid (*preferred_gid) == NULL) {
+ *gid = *preferred_gid;
+ return 0;
+ }
+ /*
+ * gr_locate_gid() found the GID in an as-yet uncommitted
+ * entry. We'll proceed below and auto-set a GID.
+ */
+ } else if (result == EEXIST || result == ERANGE || result == EINVAL) {
+ /*
+ * Continue on below. At this time, we won't
+ * treat these three cases differently.
+ */
+ } else {
+ /*
+ * An unexpected error occurred. We should report
+ * this and fail the group creation.
+ * This differs from the automatic creation
+ * behavior below, since if a specific GID 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 GID: %s\n"),
+ log_get_progname(), strerror (result));
+ return -1;
+ }
+ }
+
+ /*
+ * Search the entire group file,
+ * looking for the next unused value.
+ *
+ * We first check the local database with gr_rewind/gr_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 groups) or highest (non-system
+ * groups), we will prefer those and avoid potentially reclaiming a
+ * deleted group (which can be a security issue, since it may grant
+ * access to files belonging to that former group).
+ *
+ * If there are no GIDs 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 GIDs */
+ used_gids = CALLOC (gid_max + 1, bool);
+ if (NULL == used_gids) {
+ fprintf (log_get_logfd(),
+ _("%s: failed to allocate memory: %s\n"),
+ log_get_progname(), strerror (errno));
+ return -1;
+ }
+
+ /* First look for the lowest and highest value in the local database */
+ (void) gr_rewind ();
+ highest_found = gid_min;
+ lowest_found = gid_max;
+ while ((grp = gr_next ()) != NULL) {
+ /*
+ * Does this entry have a lower GID than the lowest we've found
+ * so far?
+ */
+ if ((grp->gr_gid <= lowest_found) && (grp->gr_gid >= gid_min)) {
+ lowest_found = grp->gr_gid - 1;
+ }
+
+ /*
+ * Does this entry have a higher GID than the highest we've found
+ * so far?
+ */
+ if ((grp->gr_gid >= highest_found) && (grp->gr_gid <= gid_max)) {
+ highest_found = grp->gr_gid + 1;
+ }
+
+ /* create index of used GIDs */
+ if (grp->gr_gid >= gid_min
+ && grp->gr_gid <= gid_max) {
+
+ used_gids[grp->gr_gid] = true;
+ }
+ }
+
+ if (sys_group) {
+ /*
+ * For system groups, we want to start from the
+ * top of the range and work downwards.
+ */
+
+ /*
+ * At the conclusion of the gr_next() search, we will either
+ * have a presumed-free GID or we will be at GID_MIN - 1.
+ */
+ if (lowest_found < gid_min) {
+ /*
+ * In this case, a GID is in use at GID_MIN.
+ *
+ * We will reset the search to GID_MAX and proceed down
+ * through all the GIDs (skipping those we detected with
+ * used_gids) for a free one. It is a known issue that
+ * this may result in reusing a previously-deleted GID,
+ * so administrators should be instructed to use this
+ * auto-detection with care (and prefer to assign GIDs
+ * explicitly).
+ */
+ lowest_found = gid_max;
+ }
+
+ /* Search through all of the IDs in the range */
+ for (id = lowest_found; id >= gid_min; id--) {
+ result = check_gid (id, gid_min, gid_max, used_gids);
+ if (result == 0) {
+ /* This GID is available. Return it. */
+ *gid = id;
+ free (used_gids);
+ return 0;
+ } else if (result == EEXIST || result == EINVAL) {
+ /*
+ * This GID is in use or unusable, 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 GID (%s). "
+ "Suppressing additional messages.\n"),
+ log_get_progname(), strerror (result));
+ SYSLOG ((LOG_ERR,
+ "Error checking available GIDs: %s",
+ strerror (result)));
+ nospam = 1;
+ }
+ /*
+ * We will continue anyway. Hopefully a later GID
+ * will work properly.
+ */
+ }
+ }
+
+ /*
+ * If we get all the way through the loop, try again from GID_MAX,
+ * unless that was where we previously started. (NOTE: the worst-case
+ * scenario here is that we will run through (GID_MAX - GID_MIN - 1)
+ * cycles *again* if we fall into this case with lowest_found as
+ * GID_MAX - 1, all groups in the range in use and maintained by
+ * network services such as LDAP.)
+ */
+ if (lowest_found != gid_max) {
+ for (id = gid_max; id >= gid_min; id--) {
+ result = check_gid (id, gid_min, gid_max, used_gids);
+ if (result == 0) {
+ /* This GID is available. Return it. */
+ *gid = id;
+ free (used_gids);
+ return 0;
+ } else if (result == EEXIST || result == EINVAL) {
+ /*
+ * This GID is in use or unusable, 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 GID (%s). "
+ "Suppressing additional messages.\n"),
+ log_get_progname(), strerror (result));
+ SYSLOG ((LOG_ERR,
+ "Error checking available GIDs: %s",
+ strerror (result)));
+ nospam = 1;
+ }
+ /*
+ * We will continue anyway. Hopefully a later GID
+ * will work properly.
+ */
+ }
+ }
+ }
+ } else { /* !sys_group */
+ /*
+ * For non-system groups, we want to start from the
+ * bottom of the range and work upwards.
+ */
+
+ /*
+ * At the conclusion of the gr_next() search, we will either
+ * have a presumed-free GID or we will be at GID_MAX + 1.
+ */
+ if (highest_found > gid_max) {
+ /*
+ * In this case, a GID is in use at GID_MAX.
+ *
+ * We will reset the search to GID_MIN and proceed up
+ * through all the GIDs (skipping those we detected with
+ * used_gids) for a free one. It is a known issue that
+ * this may result in reusing a previously-deleted GID,
+ * so administrators should be instructed to use this
+ * auto-detection with care (and prefer to assign GIDs
+ * explicitly).
+ */
+ highest_found = gid_min;
+ }
+
+ /* Search through all of the IDs in the range */
+ for (id = highest_found; id <= gid_max; id++) {
+ result = check_gid (id, gid_min, gid_max, used_gids);
+ if (result == 0) {
+ /* This GID is available. Return it. */
+ *gid = id;
+ free (used_gids);
+ return 0;
+ } else if (result == EEXIST || result == EINVAL) {
+ /*
+ * This GID is in use or unusable, 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 GID (%s). "
+ "Suppressing additional messages.\n"),
+ log_get_progname(), strerror (result));
+ SYSLOG ((LOG_ERR,
+ "Error checking available GIDs: %s",
+ strerror (result)));
+ nospam = 1;
+ }
+ /*
+ * We will continue anyway. Hopefully a later GID
+ * will work properly.
+ */
+ }
+ }
+
+ /*
+ * If we get all the way through the loop, try again from GID_MIN,
+ * unless that was where we previously started. (NOTE: the worst-case
+ * scenario here is that we will run through (GID_MAX - GID_MIN - 1)
+ * cycles *again* if we fall into this case with highest_found as
+ * GID_MIN + 1, all groups in the range in use and maintained by
+ * network services such as LDAP.)
+ */
+ if (highest_found != gid_min) {
+ for (id = gid_min; id <= gid_max; id++) {
+ result = check_gid (id, gid_min, gid_max, used_gids);
+ if (result == 0) {
+ /* This GID is available. Return it. */
+ *gid = id;
+ free (used_gids);
+ return 0;
+ } else if (result == EEXIST || result == EINVAL) {
+ /*
+ * This GID is in use or unusable, 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 GID (%s). "
+ "Suppressing additional messages.\n"),
+ log_get_progname(), strerror (result));
+ SYSLOG ((LOG_ERR,
+ "Error checking available GIDs: %s",
+ strerror (result)));
+ nospam = 1;
+ }
+ /*
+ * We will continue anyway. Hopefully a later GID
+ * will work properly.
+ */
+ }
+ }
+ }
+ }
+
+ /* The code reached here and found no available IDs in the range */
+ fprintf (log_get_logfd(),
+ _("%s: Can't get unique GID (no more available GIDs)\n"),
+ log_get_progname());
+ SYSLOG ((LOG_WARN, "no more available GIDs on the system"));
+ free (used_gids);
+ return -1;
+}
+
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