baae5b4a06
Some programs don't support `(uint16_t) -1` or `(uint32_t) -1` as user or group IDs. This is because `-1` is used as an error code or as an unspecified ID, e.g. in `chown(2)` parameters, and in the past, `gid_t` and `uid_t` have changed width. For legacy reasons, those values have been kept reserved in programs today (for example systemd does this; see the documentation in the link below). This should not be confused with catching overflow in the ID values, since that is already caught by our ERANGE checks. This is about not using reserved values that have been reserved for legacy reasons. Link: <https://systemd.io/UIDS-GIDS/> Reviewed-by: Alejandro Colomar <alx@kernel.org> Signed-off-by: Martin Kletzander <mkletzan@redhat.com>
501 lines
14 KiB
C
501 lines
14 KiB
C
/*
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* SPDX-FileCopyrightText: 1991 - 1994, Julianne Frances Haugh
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* SPDX-FileCopyrightText: 2008 - 2011, Nicolas François
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* SPDX-FileCopyrightText: 2014, Red Hat, Inc.
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*
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* SPDX-License-Identifier: BSD-3-Clause
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*/
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#include <config.h>
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#include <assert.h>
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#include <stdio.h>
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#include <errno.h>
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#include "prototypes.h"
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#include "groupio.h"
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#include "getdef.h"
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#include "shadowlog.h"
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/*
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* get_ranges - Get the minimum and maximum ID ranges for the search
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*
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* This function will return the minimum and maximum ranges for IDs
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*
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* 0: The function completed successfully
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* EINVAL: The provided ranges are impossible (such as maximum < minimum)
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*
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* preferred_min: The special-case minimum value for a specifically-
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* requested ID, which may be lower than the standard min_id
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*/
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static int get_ranges (bool sys_group, gid_t *min_id, gid_t *max_id,
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gid_t *preferred_min)
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{
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gid_t gid_def_max = 0;
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if (sys_group) {
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/* System groups */
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/* A requested ID is allowed to be below the autoselect range */
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*preferred_min = (gid_t) 1;
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/* Get the minimum ID range from login.defs or default to 101 */
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*min_id = getdef_ulong ("SYS_GID_MIN", 101UL);
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/*
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* If SYS_GID_MAX is unspecified, we should assume it to be one
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* less than the GID_MIN (which is reserved for non-system accounts)
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*/
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gid_def_max = getdef_ulong ("GID_MIN", 1000UL) - 1;
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*max_id = getdef_ulong ("SYS_GID_MAX", gid_def_max);
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/* Check that the ranges make sense */
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if (*max_id < *min_id) {
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(void) fprintf (log_get_logfd(),
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_("%s: Invalid configuration: SYS_GID_MIN (%lu), "
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"GID_MIN (%lu), SYS_GID_MAX (%lu)\n"),
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log_get_progname(), (unsigned long) *min_id,
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getdef_ulong ("GID_MIN", 1000UL),
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(unsigned long) *max_id);
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return EINVAL;
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}
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/*
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* Zero is reserved for root and the allocation algorithm does not
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* work right with it.
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*/
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if (*min_id == 0) {
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*min_id = (gid_t) 1;
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}
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} else {
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/* Non-system groups */
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/* Get the values from login.defs or use reasonable defaults */
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*min_id = getdef_ulong ("GID_MIN", 1000UL);
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*max_id = getdef_ulong ("GID_MAX", 60000UL);
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/*
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* The preferred minimum should match the standard ID minimum
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* for non-system groups.
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*/
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*preferred_min = *min_id;
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/* Check that the ranges make sense */
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if (*max_id < *min_id) {
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(void) fprintf (log_get_logfd(),
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_("%s: Invalid configuration: GID_MIN (%lu), "
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"GID_MAX (%lu)\n"),
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log_get_progname(), (unsigned long) *min_id,
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(unsigned long) *max_id);
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return EINVAL;
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}
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}
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return 0;
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}
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/*
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* check_gid - See if the requested GID is available
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*
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* On success, return 0
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* If the ID is in use, return EEXIST
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* If the ID might clash with -1, return EINVAL
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* If the ID is outside the range, return ERANGE
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* In other cases, return errno from getgrgid()
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*/
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static int check_gid (const gid_t gid,
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const gid_t gid_min,
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const gid_t gid_max,
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const bool *used_gids)
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{
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/* First test that the preferred ID is in the range */
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if (gid < gid_min || gid > gid_max) {
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return ERANGE;
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}
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/* Check for compatibility with 16b and 32b gid_t error codes */
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if (gid == UINT16_MAX || gid == UINT32_MAX) {
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return EINVAL;
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}
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/*
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* Check whether we already detected this GID
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* using the gr_next() loop
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*/
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if (used_gids != NULL && used_gids[gid]) {
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return EEXIST;
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}
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/* Check if the GID exists according to NSS */
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errno = 0;
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if (prefix_getgrgid (gid) != NULL) {
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return EEXIST;
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} else {
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/* getgrgid() was NULL
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* we have to ignore errors as temporary
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* failures of remote user identity services
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* would completely block user/group creation
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*/
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}
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/* If we've made it here, the GID must be available */
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return 0;
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}
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/*
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* find_new_gid - Find a new unused GID.
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*
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* If successful, find_new_gid provides an unused group ID in the
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* [GID_MIN:GID_MAX] range.
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* This ID should be higher than all the used GID, but if not possible,
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* the lowest unused ID in the range will be returned.
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*
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* Return 0 on success, -1 if no unused GIDs are available.
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*/
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int find_new_gid (bool sys_group,
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gid_t *gid,
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/*@null@*/gid_t const *preferred_gid)
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{
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bool *used_gids;
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const struct group *grp;
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gid_t gid_min, gid_max, preferred_min;
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gid_t id;
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gid_t lowest_found, highest_found;
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int result;
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int nospam = 0;
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assert(gid != NULL);
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/*
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* First, figure out what ID range is appropriate for
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* automatic assignment
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*/
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result = get_ranges (sys_group, &gid_min, &gid_max, &preferred_min);
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if (result == EINVAL) {
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return -1;
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}
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/* Check if the preferred GID is available */
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if (preferred_gid) {
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result = check_gid (*preferred_gid, preferred_min, gid_max, NULL);
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if (result == 0) {
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/*
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* Make sure the GID isn't queued for use already
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*/
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if (gr_locate_gid (*preferred_gid) == NULL) {
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*gid = *preferred_gid;
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return 0;
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}
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/*
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* gr_locate_gid() found the GID in an as-yet uncommitted
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* entry. We'll proceed below and auto-set a GID.
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*/
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} else if (result == EEXIST || result == ERANGE || result == EINVAL) {
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/*
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* Continue on below. At this time, we won't
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* treat these three cases differently.
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*/
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} else {
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/*
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* An unexpected error occurred. We should report
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* this and fail the group creation.
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* This differs from the automatic creation
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* behavior below, since if a specific GID was
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* requested and generated an error, the user is
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* more likely to want to stop and address the
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* issue.
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*/
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fprintf (log_get_logfd(),
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_("%s: Encountered error attempting to use "
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"preferred GID: %s\n"),
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log_get_progname(), strerror (result));
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return -1;
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}
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}
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/*
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* Search the entire group file,
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* looking for the next unused value.
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*
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* We first check the local database with gr_rewind/gr_next to find
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* all local values that are in use.
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*
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* We then compare the next free value to all databases (local and
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* remote) and iterate until we find a free one. If there are free
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* values beyond the lowest (system groups) or highest (non-system
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* groups), we will prefer those and avoid potentially reclaiming a
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* deleted group (which can be a security issue, since it may grant
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* access to files belonging to that former group).
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*
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* If there are no GIDs available at the end of the search, we will
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* have no choice but to iterate through the range looking for gaps.
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*
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*/
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/* Create an array to hold all of the discovered GIDs */
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used_gids = malloc (sizeof (bool) * (gid_max +1));
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if (NULL == used_gids) {
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fprintf (log_get_logfd(),
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_("%s: failed to allocate memory: %s\n"),
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log_get_progname(), strerror (errno));
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return -1;
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}
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memset (used_gids, false, sizeof (bool) * (gid_max + 1));
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/* First look for the lowest and highest value in the local database */
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(void) gr_rewind ();
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highest_found = gid_min;
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lowest_found = gid_max;
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while ((grp = gr_next ()) != NULL) {
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/*
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* Does this entry have a lower GID than the lowest we've found
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* so far?
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*/
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if ((grp->gr_gid <= lowest_found) && (grp->gr_gid >= gid_min)) {
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lowest_found = grp->gr_gid - 1;
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}
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/*
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* Does this entry have a higher GID than the highest we've found
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* so far?
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*/
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if ((grp->gr_gid >= highest_found) && (grp->gr_gid <= gid_max)) {
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highest_found = grp->gr_gid + 1;
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}
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/* create index of used GIDs */
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if (grp->gr_gid >= gid_min
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&& grp->gr_gid <= gid_max) {
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used_gids[grp->gr_gid] = true;
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}
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}
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if (sys_group) {
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/*
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* For system groups, we want to start from the
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* top of the range and work downwards.
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*/
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/*
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* At the conclusion of the gr_next() search, we will either
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* have a presumed-free GID or we will be at GID_MIN - 1.
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*/
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if (lowest_found < gid_min) {
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/*
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* In this case, a GID is in use at GID_MIN.
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*
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* We will reset the search to GID_MAX and proceed down
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* through all the GIDs (skipping those we detected with
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* used_gids) for a free one. It is a known issue that
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* this may result in reusing a previously-deleted GID,
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* so administrators should be instructed to use this
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* auto-detection with care (and prefer to assign GIDs
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* explicitly).
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*/
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lowest_found = gid_max;
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}
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/* Search through all of the IDs in the range */
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for (id = lowest_found; id >= gid_min; id--) {
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result = check_gid (id, gid_min, gid_max, used_gids);
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if (result == 0) {
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/* This GID is available. Return it. */
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*gid = id;
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free (used_gids);
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return 0;
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} else if (result == EEXIST || result == EINVAL) {
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/*
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* This GID is in use or unusable, we'll
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* continue to the next.
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*/
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} else {
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/*
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* An unexpected error occurred.
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*
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* Only report it the first time to avoid spamming
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* the logs
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*
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*/
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if (!nospam) {
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fprintf (log_get_logfd(),
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_("%s: Can't get unique system GID (%s). "
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"Suppressing additional messages.\n"),
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log_get_progname(), strerror (result));
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SYSLOG ((LOG_ERR,
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"Error checking available GIDs: %s",
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strerror (result)));
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nospam = 1;
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}
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/*
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* We will continue anyway. Hopefully a later GID
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* will work properly.
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*/
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}
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}
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/*
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* If we get all the way through the loop, try again from GID_MAX,
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* unless that was where we previously started. (NOTE: the worst-case
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* scenario here is that we will run through (GID_MAX - GID_MIN - 1)
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* cycles *again* if we fall into this case with lowest_found as
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* GID_MAX - 1, all groups in the range in use and maintained by
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* network services such as LDAP.)
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*/
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if (lowest_found != gid_max) {
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for (id = gid_max; id >= gid_min; id--) {
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result = check_gid (id, gid_min, gid_max, used_gids);
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if (result == 0) {
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/* This GID is available. Return it. */
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*gid = id;
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free (used_gids);
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return 0;
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} else if (result == EEXIST || result == EINVAL) {
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/*
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* This GID is in use or unusable, we'll
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* continue to the next.
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*/
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} else {
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/*
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* An unexpected error occurred.
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*
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* Only report it the first time to avoid spamming
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* the logs
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*
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*/
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if (!nospam) {
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fprintf (log_get_logfd(),
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_("%s: Can't get unique system GID (%s). "
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"Suppressing additional messages.\n"),
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log_get_progname(), strerror (result));
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SYSLOG ((LOG_ERR,
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"Error checking available GIDs: %s",
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strerror (result)));
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nospam = 1;
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}
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/*
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* We will continue anyway. Hopefully a later GID
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* will work properly.
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*/
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}
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}
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}
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} else { /* !sys_group */
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/*
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* For non-system groups, we want to start from the
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* bottom of the range and work upwards.
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*/
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/*
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* At the conclusion of the gr_next() search, we will either
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* have a presumed-free GID or we will be at GID_MAX + 1.
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*/
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if (highest_found > gid_max) {
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/*
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* In this case, a GID is in use at GID_MAX.
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*
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* We will reset the search to GID_MIN and proceed up
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* through all the GIDs (skipping those we detected with
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* used_gids) for a free one. It is a known issue that
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* this may result in reusing a previously-deleted GID,
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* so administrators should be instructed to use this
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* auto-detection with care (and prefer to assign GIDs
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* explicitly).
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*/
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highest_found = gid_min;
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}
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/* Search through all of the IDs in the range */
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for (id = highest_found; id <= gid_max; id++) {
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result = check_gid (id, gid_min, gid_max, used_gids);
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if (result == 0) {
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/* This GID is available. Return it. */
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*gid = id;
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free (used_gids);
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return 0;
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} else if (result == EEXIST || result == EINVAL) {
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/*
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* This GID is in use or unusable, we'll
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* continue to the next.
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*/
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} else {
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/*
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* An unexpected error occurred.
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*
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* Only report it the first time to avoid spamming
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* the logs
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*
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*/
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if (!nospam) {
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fprintf (log_get_logfd(),
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_("%s: Can't get unique GID (%s). "
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"Suppressing additional messages.\n"),
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log_get_progname(), strerror (result));
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SYSLOG ((LOG_ERR,
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"Error checking available GIDs: %s",
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strerror (result)));
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nospam = 1;
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}
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/*
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* We will continue anyway. Hopefully a later GID
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* will work properly.
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*/
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}
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}
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/*
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* If we get all the way through the loop, try again from GID_MIN,
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* unless that was where we previously started. (NOTE: the worst-case
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* scenario here is that we will run through (GID_MAX - GID_MIN - 1)
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* cycles *again* if we fall into this case with highest_found as
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* GID_MIN + 1, all groups in the range in use and maintained by
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* network services such as LDAP.)
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*/
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if (highest_found != gid_min) {
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for (id = gid_min; id <= gid_max; id++) {
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result = check_gid (id, gid_min, gid_max, used_gids);
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if (result == 0) {
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/* This GID is available. Return it. */
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*gid = id;
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free (used_gids);
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return 0;
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} else if (result == EEXIST || result == EINVAL) {
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/*
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* This GID is in use or unusable, we'll
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* continue to the next.
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*/
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} else {
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/*
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* An unexpected error occurred.
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*
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* Only report it the first time to avoid spamming
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* the logs
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*
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*/
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if (!nospam) {
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fprintf (log_get_logfd(),
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_("%s: Can't get unique GID (%s). "
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"Suppressing additional messages.\n"),
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log_get_progname(), strerror (result));
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SYSLOG ((LOG_ERR,
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"Error checking available GIDs: %s",
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strerror (result)));
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nospam = 1;
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}
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/*
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* We will continue anyway. Hopefully a later GID
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* will work properly.
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*/
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}
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}
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}
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}
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/* The code reached here and found no available IDs in the range */
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fprintf (log_get_logfd(),
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_("%s: Can't get unique GID (no more available GIDs)\n"),
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log_get_progname());
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SYSLOG ((LOG_WARN, "no more available GIDs on the system"));
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free (used_gids);
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return -1;
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}
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