user.c 5.3 KB

123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960616263646566676869707172737475767778798081828384858687888990919293949596979899100101102103104105106107108109110111112113114115116117118119120121122123124125126127128129130131132133134135136137138139140141142143144145146147148149150151152153154155156157158159160161162163164165166167168169170171172173174175176177178179180181182183184185186187188189190191192193194195196197198199200201202203204205206207208209210211212213214215216217218219220221222223224225226
  1. /*
  2. * The "user cache".
  3. *
  4. * (C) Copyright 1991-2000 Linus Torvalds
  5. *
  6. * We have a per-user structure to keep track of how many
  7. * processes, files etc the user has claimed, in order to be
  8. * able to have per-user limits for system resources.
  9. */
  10. #include <linux/init.h>
  11. #include <linux/sched.h>
  12. #include <linux/slab.h>
  13. #include <linux/bitops.h>
  14. #include <linux/key.h>
  15. #include <linux/interrupt.h>
  16. #include <linux/export.h>
  17. #include <linux/user_namespace.h>
  18. #include <linux/proc_ns.h>
  19. /*
  20. * userns count is 1 for root user, 1 for init_uts_ns,
  21. * and 1 for... ?
  22. */
  23. struct user_namespace init_user_ns = {
  24. .uid_map = {
  25. .nr_extents = 1,
  26. .extent[0] = {
  27. .first = 0,
  28. .lower_first = 0,
  29. .count = 4294967295U,
  30. },
  31. },
  32. .gid_map = {
  33. .nr_extents = 1,
  34. .extent[0] = {
  35. .first = 0,
  36. .lower_first = 0,
  37. .count = 4294967295U,
  38. },
  39. },
  40. .projid_map = {
  41. .nr_extents = 1,
  42. .extent[0] = {
  43. .first = 0,
  44. .lower_first = 0,
  45. .count = 4294967295U,
  46. },
  47. },
  48. .count = ATOMIC_INIT(3),
  49. .owner = GLOBAL_ROOT_UID,
  50. .group = GLOBAL_ROOT_GID,
  51. .proc_inum = PROC_USER_INIT_INO,
  52. #ifdef CONFIG_KEYS_KERBEROS_CACHE
  53. .krb_cache_register_sem =
  54. __RWSEM_INITIALIZER(init_user_ns.krb_cache_register_sem),
  55. #endif
  56. };
  57. EXPORT_SYMBOL_GPL(init_user_ns);
  58. /*
  59. * UID task count cache, to get fast user lookup in "alloc_uid"
  60. * when changing user ID's (ie setuid() and friends).
  61. */
  62. #define UIDHASH_BITS (CONFIG_BASE_SMALL ? 3 : 7)
  63. #define UIDHASH_SZ (1 << UIDHASH_BITS)
  64. #define UIDHASH_MASK (UIDHASH_SZ - 1)
  65. #define __uidhashfn(uid) (((uid >> UIDHASH_BITS) + uid) & UIDHASH_MASK)
  66. #define uidhashentry(uid) (uidhash_table + __uidhashfn((__kuid_val(uid))))
  67. static struct kmem_cache *uid_cachep;
  68. struct hlist_head uidhash_table[UIDHASH_SZ];
  69. /*
  70. * The uidhash_lock is mostly taken from process context, but it is
  71. * occasionally also taken from softirq/tasklet context, when
  72. * task-structs get RCU-freed. Hence all locking must be softirq-safe.
  73. * But free_uid() is also called with local interrupts disabled, and running
  74. * local_bh_enable() with local interrupts disabled is an error - we'll run
  75. * softirq callbacks, and they can unconditionally enable interrupts, and
  76. * the caller of free_uid() didn't expect that..
  77. */
  78. static DEFINE_SPINLOCK(uidhash_lock);
  79. /* root_user.__count is 1, for init task cred */
  80. struct user_struct root_user = {
  81. .__count = ATOMIC_INIT(1),
  82. .processes = ATOMIC_INIT(1),
  83. .files = ATOMIC_INIT(0),
  84. .sigpending = ATOMIC_INIT(0),
  85. .locked_shm = 0,
  86. .uid = GLOBAL_ROOT_UID,
  87. };
  88. /*
  89. * These routines must be called with the uidhash spinlock held!
  90. */
  91. static void uid_hash_insert(struct user_struct *up, struct hlist_head *hashent)
  92. {
  93. hlist_add_head(&up->uidhash_node, hashent);
  94. }
  95. static void uid_hash_remove(struct user_struct *up)
  96. {
  97. hlist_del_init(&up->uidhash_node);
  98. }
  99. static struct user_struct *uid_hash_find(kuid_t uid, struct hlist_head *hashent)
  100. {
  101. struct user_struct *user;
  102. hlist_for_each_entry(user, hashent, uidhash_node) {
  103. if (uid_eq(user->uid, uid)) {
  104. atomic_inc(&user->__count);
  105. return user;
  106. }
  107. }
  108. return NULL;
  109. }
  110. /* IRQs are disabled and uidhash_lock is held upon function entry.
  111. * IRQ state (as stored in flags) is restored and uidhash_lock released
  112. * upon function exit.
  113. */
  114. static void free_user(struct user_struct *up, unsigned long flags)
  115. __releases(&uidhash_lock)
  116. {
  117. uid_hash_remove(up);
  118. spin_unlock_irqrestore(&uidhash_lock, flags);
  119. key_put(up->uid_keyring);
  120. key_put(up->session_keyring);
  121. kmem_cache_free(uid_cachep, up);
  122. }
  123. /*
  124. * Locate the user_struct for the passed UID. If found, take a ref on it. The
  125. * caller must undo that ref with free_uid().
  126. *
  127. * If the user_struct could not be found, return NULL.
  128. */
  129. struct user_struct *find_user(kuid_t uid)
  130. {
  131. struct user_struct *ret;
  132. unsigned long flags;
  133. spin_lock_irqsave(&uidhash_lock, flags);
  134. ret = uid_hash_find(uid, uidhashentry(uid));
  135. spin_unlock_irqrestore(&uidhash_lock, flags);
  136. return ret;
  137. }
  138. void free_uid(struct user_struct *up)
  139. {
  140. unsigned long flags;
  141. if (!up)
  142. return;
  143. local_irq_save(flags);
  144. if (atomic_dec_and_lock(&up->__count, &uidhash_lock))
  145. free_user(up, flags);
  146. else
  147. local_irq_restore(flags);
  148. }
  149. struct user_struct *alloc_uid(kuid_t uid)
  150. {
  151. struct hlist_head *hashent = uidhashentry(uid);
  152. struct user_struct *up, *new;
  153. spin_lock_irq(&uidhash_lock);
  154. up = uid_hash_find(uid, hashent);
  155. spin_unlock_irq(&uidhash_lock);
  156. if (!up) {
  157. new = kmem_cache_zalloc(uid_cachep, GFP_KERNEL);
  158. if (!new)
  159. goto out_unlock;
  160. new->uid = uid;
  161. atomic_set(&new->__count, 1);
  162. /*
  163. * Before adding this, check whether we raced
  164. * on adding the same user already..
  165. */
  166. spin_lock_irq(&uidhash_lock);
  167. up = uid_hash_find(uid, hashent);
  168. if (up) {
  169. key_put(new->uid_keyring);
  170. key_put(new->session_keyring);
  171. kmem_cache_free(uid_cachep, new);
  172. } else {
  173. uid_hash_insert(new, hashent);
  174. up = new;
  175. }
  176. spin_unlock_irq(&uidhash_lock);
  177. }
  178. return up;
  179. out_unlock:
  180. return NULL;
  181. }
  182. static int __init uid_cache_init(void)
  183. {
  184. int n;
  185. uid_cachep = kmem_cache_create("uid_cache", sizeof(struct user_struct),
  186. 0, SLAB_HWCACHE_ALIGN|SLAB_PANIC, NULL);
  187. for(n = 0; n < UIDHASH_SZ; ++n)
  188. INIT_HLIST_HEAD(uidhash_table + n);
  189. /* Insert the root user immediately (init already runs as root) */
  190. spin_lock_irq(&uidhash_lock);
  191. uid_hash_insert(&root_user, uidhashentry(GLOBAL_ROOT_UID));
  192. spin_unlock_irq(&uidhash_lock);
  193. return 0;
  194. }
  195. module_init(uid_cache_init);