user.c 5.6 KB

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  1. // SPDX-License-Identifier: GPL-2.0-only
  2. /*
  3. * The "user cache".
  4. *
  5. * (C) Copyright 1991-2000 Linus Torvalds
  6. *
  7. * We have a per-user structure to keep track of how many
  8. * processes, files etc the user has claimed, in order to be
  9. * able to have per-user limits for system resources.
  10. */
  11. #include <linux/init.h>
  12. #include <linux/sched.h>
  13. #include <linux/slab.h>
  14. #include <linux/bitops.h>
  15. #include <linux/key.h>
  16. #include <linux/sched/user.h>
  17. #include <linux/interrupt.h>
  18. #include <linux/export.h>
  19. #include <linux/user_namespace.h>
  20. #include <linux/proc_ns.h>
  21. /*
  22. * userns count is 1 for root user, 1 for init_uts_ns,
  23. * and 1 for... ?
  24. */
  25. struct user_namespace init_user_ns = {
  26. .uid_map = {
  27. .nr_extents = 1,
  28. {
  29. .extent[0] = {
  30. .first = 0,
  31. .lower_first = 0,
  32. .count = 4294967295U,
  33. },
  34. },
  35. },
  36. .gid_map = {
  37. .nr_extents = 1,
  38. {
  39. .extent[0] = {
  40. .first = 0,
  41. .lower_first = 0,
  42. .count = 4294967295U,
  43. },
  44. },
  45. },
  46. .projid_map = {
  47. .nr_extents = 1,
  48. {
  49. .extent[0] = {
  50. .first = 0,
  51. .lower_first = 0,
  52. .count = 4294967295U,
  53. },
  54. },
  55. },
  56. .count = ATOMIC_INIT(3),
  57. .owner = GLOBAL_ROOT_UID,
  58. .group = GLOBAL_ROOT_GID,
  59. .ns.inum = PROC_USER_INIT_INO,
  60. #ifdef CONFIG_USER_NS
  61. .ns.ops = &userns_operations,
  62. #endif
  63. .flags = USERNS_INIT_FLAGS,
  64. #ifdef CONFIG_KEYS
  65. .keyring_name_list = LIST_HEAD_INIT(init_user_ns.keyring_name_list),
  66. .keyring_sem = __RWSEM_INITIALIZER(init_user_ns.keyring_sem),
  67. #endif
  68. };
  69. EXPORT_SYMBOL_GPL(init_user_ns);
  70. /*
  71. * UID task count cache, to get fast user lookup in "alloc_uid"
  72. * when changing user ID's (ie setuid() and friends).
  73. */
  74. #define UIDHASH_BITS (CONFIG_BASE_SMALL ? 3 : 7)
  75. #define UIDHASH_SZ (1 << UIDHASH_BITS)
  76. #define UIDHASH_MASK (UIDHASH_SZ - 1)
  77. #define __uidhashfn(uid) (((uid >> UIDHASH_BITS) + uid) & UIDHASH_MASK)
  78. #define uidhashentry(uid) (uidhash_table + __uidhashfn((__kuid_val(uid))))
  79. static struct kmem_cache *uid_cachep;
  80. static struct hlist_head uidhash_table[UIDHASH_SZ];
  81. /*
  82. * The uidhash_lock is mostly taken from process context, but it is
  83. * occasionally also taken from softirq/tasklet context, when
  84. * task-structs get RCU-freed. Hence all locking must be softirq-safe.
  85. * But free_uid() is also called with local interrupts disabled, and running
  86. * local_bh_enable() with local interrupts disabled is an error - we'll run
  87. * softirq callbacks, and they can unconditionally enable interrupts, and
  88. * the caller of free_uid() didn't expect that..
  89. */
  90. static DEFINE_SPINLOCK(uidhash_lock);
  91. /* root_user.__count is 1, for init task cred */
  92. struct user_struct root_user = {
  93. .__count = REFCOUNT_INIT(1),
  94. .processes = ATOMIC_INIT(1),
  95. .sigpending = ATOMIC_INIT(0),
  96. .locked_shm = 0,
  97. .uid = GLOBAL_ROOT_UID,
  98. .ratelimit = RATELIMIT_STATE_INIT(root_user.ratelimit, 0, 0),
  99. };
  100. /*
  101. * These routines must be called with the uidhash spinlock held!
  102. */
  103. static void uid_hash_insert(struct user_struct *up, struct hlist_head *hashent)
  104. {
  105. hlist_add_head(&up->uidhash_node, hashent);
  106. }
  107. static void uid_hash_remove(struct user_struct *up)
  108. {
  109. hlist_del_init(&up->uidhash_node);
  110. }
  111. static struct user_struct *uid_hash_find(kuid_t uid, struct hlist_head *hashent)
  112. {
  113. struct user_struct *user;
  114. hlist_for_each_entry(user, hashent, uidhash_node) {
  115. if (uid_eq(user->uid, uid)) {
  116. refcount_inc(&user->__count);
  117. return user;
  118. }
  119. }
  120. return NULL;
  121. }
  122. /* IRQs are disabled and uidhash_lock is held upon function entry.
  123. * IRQ state (as stored in flags) is restored and uidhash_lock released
  124. * upon function exit.
  125. */
  126. static void free_user(struct user_struct *up, unsigned long flags)
  127. __releases(&uidhash_lock)
  128. {
  129. uid_hash_remove(up);
  130. spin_unlock_irqrestore(&uidhash_lock, flags);
  131. kmem_cache_free(uid_cachep, up);
  132. }
  133. /*
  134. * Locate the user_struct for the passed UID. If found, take a ref on it. The
  135. * caller must undo that ref with free_uid().
  136. *
  137. * If the user_struct could not be found, return NULL.
  138. */
  139. struct user_struct *find_user(kuid_t uid)
  140. {
  141. struct user_struct *ret;
  142. unsigned long flags;
  143. spin_lock_irqsave(&uidhash_lock, flags);
  144. ret = uid_hash_find(uid, uidhashentry(uid));
  145. spin_unlock_irqrestore(&uidhash_lock, flags);
  146. return ret;
  147. }
  148. EXPORT_SYMBOL_GPL(find_user);
  149. void free_uid(struct user_struct *up)
  150. {
  151. unsigned long flags;
  152. if (!up)
  153. return;
  154. if (refcount_dec_and_lock_irqsave(&up->__count, &uidhash_lock, &flags))
  155. free_user(up, flags);
  156. }
  157. EXPORT_SYMBOL_GPL(free_uid);
  158. struct user_struct *alloc_uid(kuid_t uid)
  159. {
  160. struct hlist_head *hashent = uidhashentry(uid);
  161. struct user_struct *up, *new;
  162. spin_lock_irq(&uidhash_lock);
  163. up = uid_hash_find(uid, hashent);
  164. spin_unlock_irq(&uidhash_lock);
  165. if (!up) {
  166. new = kmem_cache_zalloc(uid_cachep, GFP_KERNEL);
  167. if (!new)
  168. return NULL;
  169. new->uid = uid;
  170. refcount_set(&new->__count, 1);
  171. ratelimit_state_init(&new->ratelimit, HZ, 100);
  172. ratelimit_set_flags(&new->ratelimit, RATELIMIT_MSG_ON_RELEASE);
  173. /*
  174. * Before adding this, check whether we raced
  175. * on adding the same user already..
  176. */
  177. spin_lock_irq(&uidhash_lock);
  178. up = uid_hash_find(uid, hashent);
  179. if (up) {
  180. kmem_cache_free(uid_cachep, new);
  181. } else {
  182. uid_hash_insert(new, hashent);
  183. up = new;
  184. }
  185. spin_unlock_irq(&uidhash_lock);
  186. }
  187. return up;
  188. }
  189. static int __init uid_cache_init(void)
  190. {
  191. int n;
  192. uid_cachep = kmem_cache_create("uid_cache", sizeof(struct user_struct),
  193. 0, SLAB_HWCACHE_ALIGN|SLAB_PANIC, NULL);
  194. for(n = 0; n < UIDHASH_SZ; ++n)
  195. INIT_HLIST_HEAD(uidhash_table + n);
  196. /* Insert the root user immediately (init already runs as root) */
  197. spin_lock_irq(&uidhash_lock);
  198. uid_hash_insert(&root_user, uidhashentry(GLOBAL_ROOT_UID));
  199. spin_unlock_irq(&uidhash_lock);
  200. return 0;
  201. }
  202. subsys_initcall(uid_cache_init);