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shadow/libmisc/find_new_gid.c

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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 "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 = (gid_t) 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 = (gid_t) getdef_ulong ("GID_MIN", 1000UL) - 1;
*max_id = (gid_t) getdef_ulong ("SYS_GID_MAX",
(unsigned long) 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;
}
} else {
/* Non-system groups */
/* Get the values from login.defs or use reasonable defaults */
*min_id = (gid_t) getdef_ulong ("GID_MIN", 1000UL);
*max_id = (gid_t) 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 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,
bool *used_gids)
{
/* First test that the preferred ID is in the range */
if (gid < gid_min || gid > gid_max) {
return ERANGE;
}
/*
* 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) {
/*
* 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 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 = malloc (sizeof (bool) * (gid_max +1));
if (NULL == used_gids) {
fprintf (log_get_logfd(),
_("%s: failed to allocate memory: %s\n"),
log_get_progname(), strerror (errno));
return -1;
}
memset (used_gids, false, sizeof (bool) * (gid_max + 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) {
/* This GID 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 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) {
/* This GID 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 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) {
/* This GID 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 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) {
/* This GID 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 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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