2 * Copyright (c) 1991 - 1994, Julianne Frances Haugh
3 * Copyright (c) 2008 , Nicolas François
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36 #include "prototypes.h"
41 * find_new_uid - Find a new unused UID.
43 * If successful, find_new_uid provides an unused user ID in the
44 * [UID_MIN:UID_MAX] range.
45 * This ID should be higher than all the used UID, but if not possible,
46 * the lowest unused ID in the range will be returned.
48 * Return 0 on success, -1 if no unused UIDs are available.
50 int find_new_uid (bool sys_user, uid_t *uid, uid_t const *preferred_uid)
52 const struct passwd *pwd;
53 uid_t uid_min, uid_max, user_id;
59 uid_min = getdef_ulong ("UID_MIN", 1000L);
60 uid_max = getdef_ulong ("UID_MAX", 60000L);
62 uid_min = getdef_ulong ("SYS_UID_MIN", 1L);
63 uid_max = getdef_ulong ("UID_MIN", 1000L) - 1;
64 uid_max = getdef_ulong ("SYS_UID_MAX", (unsigned long) uid_max);
66 used_uids = alloca (sizeof (char) * uid_max +1);
67 memset (used_uids, 0, sizeof (char) * uid_max + 1);
69 if ( (NULL != preferred_uid)
70 && (*preferred_uid >= uid_min)
71 && (*preferred_uid <= uid_max)
72 /* Check if the user exists according to NSS */
73 && (getpwuid (*preferred_uid) == NULL)
74 /* Check also the local database in case of uncommitted
76 && (pw_locate_uid (*preferred_uid) == NULL)) {
77 *uid = *preferred_uid;
85 * Search the entire password file,
86 * looking for the largest unused value.
88 * We check the list of users according to NSS (setpwent/getpwent),
89 * but we also check the local database (pw_rewind/pw_next) in case
90 * some users were created but the changes were not committed yet.
94 while ( ((pwd = getpwent ()) != NULL)
95 || ((pwd = pw_next ()) != NULL)) {
96 if ((pwd->pw_uid >= user_id) && (pwd->pw_uid <= uid_max)) {
97 user_id = pwd->pw_uid + 1;
99 /* create index of used UIDs */
100 if (pwd->pw_uid <= uid_max) {
101 used_uids[pwd->pw_uid] = 1;
107 * If a user with UID equal to UID_MAX exists, the above algorithm
108 * will give us UID_MAX+1 even if not unique. Search for the first
109 * free UID starting with UID_MIN.
111 if (user_id == uid_max + 1) {
112 for (user_id = uid_min; user_id < uid_max; user_id++) {
113 if (0 == used_uids[user_id]) {
117 if (user_id == uid_max) {
118 fprintf (stderr, _("%s: Can't get unique UID (no more available UIDs)\n"), Prog);
119 SYSLOG ((LOG_WARN, "no more available UID on the system"));