user.c 6.1 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. #include <trace/hooks/user.h>
  22. /*
  23. * userns count is 1 for root user, 1 for init_uts_ns,
  24. * and 1 for... ?
  25. */
  26. struct user_namespace init_user_ns = {
  27. .uid_map = {
  28. .nr_extents = 1,
  29. {
  30. .extent[0] = {
  31. .first = 0,
  32. .lower_first = 0,
  33. .count = 4294967295U,
  34. },
  35. },
  36. },
  37. .gid_map = {
  38. .nr_extents = 1,
  39. {
  40. .extent[0] = {
  41. .first = 0,
  42. .lower_first = 0,
  43. .count = 4294967295U,
  44. },
  45. },
  46. },
  47. .projid_map = {
  48. .nr_extents = 1,
  49. {
  50. .extent[0] = {
  51. .first = 0,
  52. .lower_first = 0,
  53. .count = 4294967295U,
  54. },
  55. },
  56. },
  57. .ns.count = REFCOUNT_INIT(3),
  58. .owner = GLOBAL_ROOT_UID,
  59. .group = GLOBAL_ROOT_GID,
  60. .ns.inum = PROC_USER_INIT_INO,
  61. #ifdef CONFIG_USER_NS
  62. .ns.ops = &userns_operations,
  63. #endif
  64. .flags = USERNS_INIT_FLAGS,
  65. #ifdef CONFIG_KEYS
  66. .keyring_name_list = LIST_HEAD_INIT(init_user_ns.keyring_name_list),
  67. .keyring_sem = __RWSEM_INITIALIZER(init_user_ns.keyring_sem),
  68. #endif
  69. };
  70. EXPORT_SYMBOL_GPL(init_user_ns);
  71. /*
  72. * UID task count cache, to get fast user lookup in "alloc_uid"
  73. * when changing user ID's (ie setuid() and friends).
  74. */
  75. #define UIDHASH_BITS (CONFIG_BASE_SMALL ? 3 : 7)
  76. #define UIDHASH_SZ (1 << UIDHASH_BITS)
  77. #define UIDHASH_MASK (UIDHASH_SZ - 1)
  78. #define __uidhashfn(uid) (((uid >> UIDHASH_BITS) + uid) & UIDHASH_MASK)
  79. #define uidhashentry(uid) (uidhash_table + __uidhashfn((__kuid_val(uid))))
  80. static struct kmem_cache *uid_cachep;
  81. static struct hlist_head uidhash_table[UIDHASH_SZ];
  82. /*
  83. * The uidhash_lock is mostly taken from process context, but it is
  84. * occasionally also taken from softirq/tasklet context, when
  85. * task-structs get RCU-freed. Hence all locking must be softirq-safe.
  86. * But free_uid() is also called with local interrupts disabled, and running
  87. * local_bh_enable() with local interrupts disabled is an error - we'll run
  88. * softirq callbacks, and they can unconditionally enable interrupts, and
  89. * the caller of free_uid() didn't expect that..
  90. */
  91. static DEFINE_SPINLOCK(uidhash_lock);
  92. /* root_user.__count is 1, for init task cred */
  93. struct user_struct root_user = {
  94. .__count = REFCOUNT_INIT(1),
  95. .uid = GLOBAL_ROOT_UID,
  96. .ratelimit = RATELIMIT_STATE_INIT(root_user.ratelimit, 0, 0),
  97. };
  98. /*
  99. * These routines must be called with the uidhash spinlock held!
  100. */
  101. static void uid_hash_insert(struct user_struct *up, struct hlist_head *hashent)
  102. {
  103. hlist_add_head(&up->uidhash_node, hashent);
  104. }
  105. static void uid_hash_remove(struct user_struct *up)
  106. {
  107. hlist_del_init(&up->uidhash_node);
  108. }
  109. static struct user_struct *uid_hash_find(kuid_t uid, struct hlist_head *hashent)
  110. {
  111. struct user_struct *user;
  112. hlist_for_each_entry(user, hashent, uidhash_node) {
  113. if (uid_eq(user->uid, uid)) {
  114. refcount_inc(&user->__count);
  115. return user;
  116. }
  117. }
  118. return NULL;
  119. }
  120. static int user_epoll_alloc(struct user_struct *up)
  121. {
  122. #ifdef CONFIG_EPOLL
  123. return percpu_counter_init(&up->epoll_watches, 0, GFP_KERNEL);
  124. #else
  125. return 0;
  126. #endif
  127. }
  128. static void user_epoll_free(struct user_struct *up)
  129. {
  130. #ifdef CONFIG_EPOLL
  131. percpu_counter_destroy(&up->epoll_watches);
  132. #endif
  133. }
  134. /* IRQs are disabled and uidhash_lock is held upon function entry.
  135. * IRQ state (as stored in flags) is restored and uidhash_lock released
  136. * upon function exit.
  137. */
  138. static void free_user(struct user_struct *up, unsigned long flags)
  139. __releases(&uidhash_lock)
  140. {
  141. trace_android_vh_free_user(up);
  142. uid_hash_remove(up);
  143. spin_unlock_irqrestore(&uidhash_lock, flags);
  144. user_epoll_free(up);
  145. kmem_cache_free(uid_cachep, up);
  146. }
  147. /*
  148. * Locate the user_struct for the passed UID. If found, take a ref on it. The
  149. * caller must undo that ref with free_uid().
  150. *
  151. * If the user_struct could not be found, return NULL.
  152. */
  153. struct user_struct *find_user(kuid_t uid)
  154. {
  155. struct user_struct *ret;
  156. unsigned long flags;
  157. spin_lock_irqsave(&uidhash_lock, flags);
  158. ret = uid_hash_find(uid, uidhashentry(uid));
  159. spin_unlock_irqrestore(&uidhash_lock, flags);
  160. return ret;
  161. }
  162. EXPORT_SYMBOL_GPL(find_user);
  163. void free_uid(struct user_struct *up)
  164. {
  165. unsigned long flags;
  166. if (!up)
  167. return;
  168. if (refcount_dec_and_lock_irqsave(&up->__count, &uidhash_lock, &flags))
  169. free_user(up, flags);
  170. }
  171. EXPORT_SYMBOL_GPL(free_uid);
  172. struct user_struct *alloc_uid(kuid_t uid)
  173. {
  174. struct hlist_head *hashent = uidhashentry(uid);
  175. struct user_struct *up, *new;
  176. spin_lock_irq(&uidhash_lock);
  177. up = uid_hash_find(uid, hashent);
  178. spin_unlock_irq(&uidhash_lock);
  179. if (!up) {
  180. new = kmem_cache_zalloc(uid_cachep, GFP_KERNEL);
  181. if (!new)
  182. return NULL;
  183. new->uid = uid;
  184. refcount_set(&new->__count, 1);
  185. trace_android_vh_alloc_uid(new);
  186. if (user_epoll_alloc(new)) {
  187. kmem_cache_free(uid_cachep, new);
  188. return NULL;
  189. }
  190. ratelimit_state_init(&new->ratelimit, HZ, 100);
  191. ratelimit_set_flags(&new->ratelimit, RATELIMIT_MSG_ON_RELEASE);
  192. /*
  193. * Before adding this, check whether we raced
  194. * on adding the same user already..
  195. */
  196. spin_lock_irq(&uidhash_lock);
  197. up = uid_hash_find(uid, hashent);
  198. if (up) {
  199. user_epoll_free(new);
  200. kmem_cache_free(uid_cachep, new);
  201. } else {
  202. uid_hash_insert(new, hashent);
  203. up = new;
  204. }
  205. spin_unlock_irq(&uidhash_lock);
  206. }
  207. return up;
  208. }
  209. static int __init uid_cache_init(void)
  210. {
  211. int n;
  212. uid_cachep = kmem_cache_create("uid_cache", sizeof(struct user_struct),
  213. 0, SLAB_HWCACHE_ALIGN|SLAB_PANIC, NULL);
  214. for(n = 0; n < UIDHASH_SZ; ++n)
  215. INIT_HLIST_HEAD(uidhash_table + n);
  216. if (user_epoll_alloc(&root_user))
  217. panic("root_user epoll percpu counter alloc failed");
  218. /* Insert the root user immediately (init already runs as root) */
  219. spin_lock_irq(&uidhash_lock);
  220. uid_hash_insert(&root_user, uidhashentry(GLOBAL_ROOT_UID));
  221. spin_unlock_irq(&uidhash_lock);
  222. return 0;
  223. }
  224. subsys_initcall(uid_cache_init);