477 lines
13 KiB
C
477 lines
13 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 "pwio.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_user, uid_t *min_id, uid_t *max_id,
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uid_t *preferred_min)
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{
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uid_t uid_def_max = 0;
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if (sys_user) {
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/* System users */
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/* A requested ID is allowed to be below the autoselect range */
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*preferred_min = (uid_t) 1;
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/* Get the minimum ID range from login.defs or default to 101 */
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*min_id = (uid_t) getdef_ulong ("SYS_UID_MIN", 101UL);
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/*
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* If SYS_UID_MAX is unspecified, we should assume it to be one
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* less than the UID_MIN (which is reserved for non-system accounts)
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*/
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uid_def_max = (uid_t) getdef_ulong ("UID_MIN", 1000UL) - 1;
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*max_id = (uid_t) getdef_ulong ("SYS_UID_MAX",
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(unsigned long) uid_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_UID_MIN (%lu), "
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"UID_MIN (%lu), SYS_UID_MAX (%lu)\n"),
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log_get_progname(), (unsigned long) *min_id,
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getdef_ulong ("UID_MIN", 1000UL),
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(unsigned long) *max_id);
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return EINVAL;
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}
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} else {
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/* Non-system users */
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/* Get the values from login.defs or use reasonable defaults */
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*min_id = (uid_t) getdef_ulong ("UID_MIN", 1000UL);
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*max_id = (uid_t) getdef_ulong ("UID_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 users.
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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: UID_MIN (%lu), "
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"UID_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_uid - See if the requested UID 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 is outside the range, return ERANGE
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* In other cases, return errno from getpwuid()
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*/
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static int check_uid(const uid_t uid,
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const uid_t uid_min,
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const uid_t uid_max,
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const bool *used_uids)
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{
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/* First test that the preferred ID is in the range */
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if (uid < uid_min || uid > uid_max) {
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return ERANGE;
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}
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/*
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* Check whether we already detected this UID
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* using the pw_next() loop
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*/
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if (used_uids != NULL && used_uids[uid]) {
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return EEXIST;
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}
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/* Check if the UID exists according to NSS */
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errno = 0;
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if (prefix_getpwuid(uid) != NULL) {
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return EEXIST;
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} else {
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/* getpwuid() 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 UID must be available */
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return 0;
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}
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/*
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* find_new_uid - Find a new unused UID.
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*
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* If successful, find_new_uid provides an unused user ID in the
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* [UID_MIN:UID_MAX] range.
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* This ID should be higher than all the used UID, 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 UIDs are available.
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*/
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int find_new_uid(bool sys_user,
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uid_t *uid,
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/*@null@*/uid_t const *preferred_uid)
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{
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bool *used_uids;
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const struct passwd *pwd;
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uid_t uid_min, uid_max, preferred_min;
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uid_t id;
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uid_t lowest_found, highest_found;
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int result;
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int nospam = 0;
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assert (uid != 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_user, &uid_min, &uid_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 UID is available */
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if (preferred_uid) {
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result = check_uid (*preferred_uid, preferred_min, uid_max, NULL);
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if (result == 0) {
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/*
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* Make sure the UID isn't queued for use already
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*/
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if (pw_locate_uid (*preferred_uid) == NULL) {
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*uid = *preferred_uid;
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return 0;
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}
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/*
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* pw_locate_uid() found the UID in an as-yet uncommitted
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* entry. We'll proceed below and auto-set an UID.
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*/
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} else if (result == EEXIST || result == ERANGE) {
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/*
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* Continue on below. At this time, we won't
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* treat these two 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 user creation.
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* This differs from the automatic creation
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* behavior below, since if a specific UID 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 UID: %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 passwd 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 pw_rewind/pw_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 users) or highest (non-system
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* users), we will prefer those and avoid potentially reclaiming a
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* deleted user (which can be a security issue, since it may grant
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* access to files belonging to that former user).
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*
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* If there are no UIDs 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 UIDs */
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used_uids = malloc (sizeof (bool) * (uid_max +1));
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if (NULL == used_uids) {
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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_uids, false, sizeof (bool) * (uid_max + 1));
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/* First look for the lowest and highest value in the local database */
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(void) pw_rewind ();
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highest_found = uid_min;
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lowest_found = uid_max;
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while ((pwd = pw_next ()) != NULL) {
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/*
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* Does this entry have a lower UID than the lowest we've found
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* so far?
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*/
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if ((pwd->pw_uid <= lowest_found) && (pwd->pw_uid >= uid_min)) {
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lowest_found = pwd->pw_uid - 1;
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}
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/*
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* Does this entry have a higher UID than the highest we've found
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* so far?
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*/
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if ((pwd->pw_uid >= highest_found) && (pwd->pw_uid <= uid_max)) {
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highest_found = pwd->pw_uid + 1;
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}
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/* create index of used UIDs */
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if (pwd->pw_uid >= uid_min
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&& pwd->pw_uid <= uid_max) {
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used_uids[pwd->pw_uid] = true;
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}
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}
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if (sys_user) {
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/*
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* For system users, 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 pw_next() search, we will either
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* have a presumed-free UID or we will be at UID_MIN - 1.
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*/
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if (lowest_found < uid_min) {
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/*
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* In this case, an UID is in use at UID_MIN.
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*
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* We will reset the search to UID_MAX and proceed down
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* through all the UIDs (skipping those we detected with
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* used_uids) for a free one. It is a known issue that
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* this may result in reusing a previously-deleted UID,
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* so administrators should be instructed to use this
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* auto-detection with care (and prefer to assign UIDs
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* explicitly).
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*/
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lowest_found = uid_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 >= uid_min; id--) {
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result = check_uid (id, uid_min, uid_max, used_uids);
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if (result == 0) {
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/* This UID is available. Return it. */
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*uid = id;
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free (used_uids);
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return 0;
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} else if (result == EEXIST) {
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/* This UID is in use, we'll continue to the next */
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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 UID (%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 UIDs: %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 UID
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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 UID_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 (UID_MAX - UID_MIN - 1)
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* cycles *again* if we fall into this case with lowest_found as
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* UID_MAX - 1, all users 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 != uid_max) {
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for (id = uid_max; id >= uid_min; id--) {
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result = check_uid (id, uid_min, uid_max, used_uids);
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if (result == 0) {
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/* This UID is available. Return it. */
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*uid = id;
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free (used_uids);
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return 0;
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} else if (result == EEXIST) {
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/* This UID is in use, we'll continue to the next */
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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 UID (%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 UIDs: %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 UID
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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_user */
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/*
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* For non-system users, 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 pw_next() search, we will either
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* have a presumed-free UID or we will be at UID_MAX + 1.
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*/
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if (highest_found > uid_max) {
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/*
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* In this case, a UID is in use at UID_MAX.
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*
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* We will reset the search to UID_MIN and proceed up
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* through all the UIDs (skipping those we detected with
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* used_uids) for a free one. It is a known issue that
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* this may result in reusing a previously-deleted UID,
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* so administrators should be instructed to use this
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* auto-detection with care (and prefer to assign UIDs
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* explicitly).
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*/
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highest_found = uid_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 <= uid_max; id++) {
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result = check_uid (id, uid_min, uid_max, used_uids);
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if (result == 0) {
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/* This UID is available. Return it. */
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*uid = id;
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free (used_uids);
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return 0;
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} else if (result == EEXIST) {
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/* This UID is in use, we'll continue to the next */
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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 UID (%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 UIDs: %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 UID
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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 UID_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 (UID_MAX - UID_MIN - 1)
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* cycles *again* if we fall into this case with highest_found as
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* UID_MIN + 1, all users 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 != uid_min) {
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for (id = uid_min; id <= uid_max; id++) {
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result = check_uid (id, uid_min, uid_max, used_uids);
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if (result == 0) {
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/* This UID is available. Return it. */
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*uid = id;
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free (used_uids);
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return 0;
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} else if (result == EEXIST) {
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/* This UID is in use, we'll continue to the next */
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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 UID (%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 UIDs: %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 UID
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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 UID (no more available UIDs)\n"),
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log_get_progname());
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SYSLOG ((LOG_WARN, "no more available UIDs on the system"));
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free (used_uids);
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return -1;
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}
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