kernel/user.c

   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
  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
  17 /*
  18  * UID task count cache, to get fast user lookup in "alloc_uid"
  19  * when changing user ID's (ie setuid() and friends).
  20  */
  21 #define UIDHASH_BITS            8
  22 #define UIDHASH_SZ              (1 << UIDHASH_BITS)
  23 #define UIDHASH_MASK            (UIDHASH_SZ - 1)
  24 #define __uidhashfn(uid)        (((uid >> UIDHASH_BITS) + uid) & UIDHASH_MASK)
  25 #define uidhashentry(uid)       (uidhash_table + __uidhashfn((uid)))
  26
  27 static kmem_cache_t *uid_cachep;
  28 static struct list_head uidhash_table[UIDHASH_SZ];
  29 static spinlock_t uidhash_lock = SPIN_LOCK_UNLOCKED;
  30
  31 struct user_struct root_user = {
  32         .__count        = ATOMIC_INIT(1),
  33         .processes      = ATOMIC_INIT(1),
  34         .files          = ATOMIC_INIT(0),
  35         .sigpending     = ATOMIC_INIT(0),
  36         .mq_bytes       = 0,
  37         .locked_shm     = 0,
  38 #ifdef CONFIG_KEYS
  39         .uid_keyring    = &root_user_keyring,
  40         .session_keyring = &root_session_keyring,
  41 #endif
  42 };
  43
  44 /*
  45  * These routines must be called with the uidhash spinlock held!
  46  */
  47 static inline void uid_hash_insert(struct user_struct *up, struct list_head *hashent)
  48 {
  49         list_add(&up->uidhash_list, hashent);
  50 }
  51
  52 static inline void uid_hash_remove(struct user_struct *up)
  53 {
  54         list_del(&up->uidhash_list);
  55 }
  56
  57 static inline struct user_struct *uid_hash_find(uid_t uid, struct list_head *hashent)
  58 {
  59         struct list_head *up;
  60
  61         list_for_each(up, hashent) {
  62                 struct user_struct *user;
  63
  64                 user = list_entry(up, struct user_struct, uidhash_list);
  65
  66                 if(user->uid == uid) {
  67                         atomic_inc(&user->__count);
  68                         return user;
  69                 }
  70         }
  71
  72         return NULL;
  73 }
  74
  75 /*
  76  * Locate the user_struct for the passed UID.  If found, take a ref on it.  The
  77  * caller must undo that ref with free_uid().
  78  *
  79  * If the user_struct could not be found, return NULL.
  80  */
  81 struct user_struct *find_user(uid_t uid)
  82 {
  83         struct user_struct *ret;
  84
  85         spin_lock(&uidhash_lock);
  86         ret = uid_hash_find(uid, uidhashentry(uid));
  87         spin_unlock(&uidhash_lock);
  88         return ret;
  89 }
  90
  91 void free_uid(struct user_struct *up)
  92 {
  93         if (up && atomic_dec_and_lock(&up->__count, &uidhash_lock)) {
  94                 uid_hash_remove(up);
  95                 key_put(up->uid_keyring);
  96                 key_put(up->session_keyring);
  97                 kmem_cache_free(uid_cachep, up);
  98                 spin_unlock(&uidhash_lock);
  99         }
 100 }
 101
 102 struct user_struct * alloc_uid(uid_t uid)
 103 {
 104         struct list_head *hashent = uidhashentry(uid);
 105         struct user_struct *up;
 106
 107         spin_lock(&uidhash_lock);
 108         up = uid_hash_find(uid, hashent);
 109         spin_unlock(&uidhash_lock);
 110
 111         if (!up) {
 112                 struct user_struct *new;
 113
 114                 new = kmem_cache_alloc(uid_cachep, SLAB_KERNEL);
 115                 if (!new)
 116                         return NULL;
 117                 new->uid = uid;
 118                 atomic_set(&new->__count, 1);
 119                 atomic_set(&new->processes, 0);
 120                 atomic_set(&new->files, 0);
 121                 atomic_set(&new->sigpending, 0);
 122
 123                 new->mq_bytes = 0;
 124                 new->locked_shm = 0;
 125
 126                 if (alloc_uid_keyring(new) < 0) {
 127                         kmem_cache_free(uid_cachep, new);
 128                         return NULL;
 129                 }
 130
 131                 /*
 132                  * Before adding this, check whether we raced
 133                  * on adding the same user already..
 134                  */
 135                 spin_lock(&uidhash_lock);
 136                 up = uid_hash_find(uid, hashent);
 137                 if (up) {
 138                         key_put(new->uid_keyring);
 139                         key_put(new->session_keyring);
 140                         kmem_cache_free(uid_cachep, new);
 141                 } else {
 142                         uid_hash_insert(new, hashent);
 143                         up = new;
 144                 }
 145                 spin_unlock(&uidhash_lock);
 146
 147         }
 148         return up;
 149 }
 150
 151 void switch_uid(struct user_struct *new_user)
 152 {
 153         struct user_struct *old_user;
 154
 155         /* What if a process setreuid()'s and this brings the
 156          * new uid over his NPROC rlimit?  We can check this now
 157          * cheaply with the new uid cache, so if it matters
 158          * we should be checking for it.  -DaveM
 159          */
 160         old_user = current->user;
 161         atomic_inc(&new_user->processes);
 162         atomic_dec(&old_user->processes);
 163         switch_uid_keyring(new_user);
 164         current->user = new_user;
 165         free_uid(old_user);
 166         suid_keys(current);
 167 }
 168
 169
 170 static int __init uid_cache_init(void)
 171 {
 172         int n;
 173
 174         uid_cachep = kmem_cache_create("uid_cache", sizeof(struct user_struct),
 175                         0, SLAB_HWCACHE_ALIGN|SLAB_PANIC, NULL, NULL);
 176
 177         for(n = 0; n < UIDHASH_SZ; ++n)
 178                 INIT_LIST_HEAD(uidhash_table + n);
 179
 180         /* Insert the root user immediately (init already runs as root) */
 181         spin_lock(&uidhash_lock);
 182         uid_hash_insert(&root_user, uidhashentry(0));
 183         spin_unlock(&uidhash_lock);
 184
 185         return 0;
 186 }
 187
 188 module_init(uid_cache_init);