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 #include <linux/interrupt.h>
  17
  18 /*
  19  * UID task count cache, to get fast user lookup in "alloc_uid"
  20  * when changing user ID's (ie setuid() and friends).
  21  */
  22
  23 #define UIDHASH_BITS (CONFIG_BASE_SMALL ? 3 : 8)
  24 #define UIDHASH_SZ              (1 << UIDHASH_BITS)
  25 #define UIDHASH_MASK            (UIDHASH_SZ - 1)
  26 #define __uidhashfn(uid)        (((uid >> UIDHASH_BITS) + uid) & UIDHASH_MASK)
  27 #define uidhashentry(uid)       (uidhash_table + __uidhashfn((uid)))
  28
  29 static kmem_cache_t *uid_cachep;
  30 static struct list_head uidhash_table[UIDHASH_SZ];
  31
  32 /*
  33  * The uidhash_lock is mostly taken from process context, but it is
  34  * occasionally also taken from softirq/tasklet context, when
  35  * task-structs get RCU-freed. Hence all locking must be softirq-safe.
  36  */
  37 static DEFINE_SPINLOCK(uidhash_lock);
  38
  39 struct user_struct root_user = {
  40         .__count        = ATOMIC_INIT(1),
  41         .processes      = ATOMIC_INIT(1),
  42         .files          = ATOMIC_INIT(0),
  43         .sigpending     = ATOMIC_INIT(0),
  44         .mq_bytes       = 0,
  45         .locked_shm     = 0,
  46 #ifdef CONFIG_KEYS
  47         .uid_keyring    = &root_user_keyring,
  48         .session_keyring = &root_session_keyring,
  49 #endif
  50 };
  51
  52 /*
  53  * These routines must be called with the uidhash spinlock held!
  54  */
  55 static inline void uid_hash_insert(struct user_struct *up, struct list_head *hashent)
  56 {
  57         list_add(&up->uidhash_list, hashent);
  58 }
  59
  60 static inline void uid_hash_remove(struct user_struct *up)
  61 {
  62         list_del(&up->uidhash_list);
  63 }
  64
  65 static inline struct user_struct *uid_hash_find(uid_t uid, struct list_head *hashent)
  66 {
  67         struct list_head *up;
  68
  69         list_for_each(up, hashent) {
  70                 struct user_struct *user;
  71
  72                 user = list_entry(up, struct user_struct, uidhash_list);
  73
  74                 if(user->uid == uid) {
  75                         atomic_inc(&user->__count);
  76                         return user;
  77                 }
  78         }
  79
  80         return NULL;
  81 }
  82
  83 /*
  84  * Locate the user_struct for the passed UID.  If found, take a ref on it.  The
  85  * caller must undo that ref with free_uid().
  86  *
  87  * If the user_struct could not be found, return NULL.
  88  */
  89 struct user_struct *find_user(uid_t uid)
  90 {
  91         struct user_struct *ret;
  92
  93         spin_lock_bh(&uidhash_lock);
  94         ret = uid_hash_find(uid, uidhashentry(uid));
  95         spin_unlock_bh(&uidhash_lock);
  96         return ret;
  97 }
  98
  99 void free_uid(struct user_struct *up)
 100 {
 101         local_bh_disable();
 102         if (up && atomic_dec_and_lock(&up->__count, &uidhash_lock)) {
 103                 uid_hash_remove(up);
 104                 key_put(up->uid_keyring);
 105                 key_put(up->session_keyring);
 106                 kmem_cache_free(uid_cachep, up);
 107                 spin_unlock(&uidhash_lock);
 108         }
 109         local_bh_enable();
 110 }
 111
 112 struct user_struct * alloc_uid(uid_t uid)
 113 {
 114         struct list_head *hashent = uidhashentry(uid);
 115         struct user_struct *up;
 116
 117         spin_lock_bh(&uidhash_lock);
 118         up = uid_hash_find(uid, hashent);
 119         spin_unlock_bh(&uidhash_lock);
 120
 121         if (!up) {
 122                 struct user_struct *new;
 123
 124                 new = kmem_cache_alloc(uid_cachep, SLAB_KERNEL);
 125                 if (!new)
 126                         return NULL;
 127                 new->uid = uid;
 128                 atomic_set(&new->__count, 1);
 129                 atomic_set(&new->processes, 0);
 130                 atomic_set(&new->files, 0);
 131                 atomic_set(&new->sigpending, 0);
 132 #ifdef CONFIG_INOTIFY
 133                 atomic_set(&new->inotify_watches, 0);
 134                 atomic_set(&new->inotify_devs, 0);
 135 #endif
 136
 137                 new->mq_bytes = 0;
 138                 new->locked_shm = 0;
 139
 140                 if (alloc_uid_keyring(new) < 0) {
 141                         kmem_cache_free(uid_cachep, new);
 142                         return NULL;
 143                 }
 144
 145                 /*
 146                  * Before adding this, check whether we raced
 147                  * on adding the same user already..
 148                  */
 149                 spin_lock_bh(&uidhash_lock);
 150                 up = uid_hash_find(uid, hashent);
 151                 if (up) {
 152                         key_put(new->uid_keyring);
 153                         key_put(new->session_keyring);
 154                         kmem_cache_free(uid_cachep, new);
 155                 } else {
 156                         uid_hash_insert(new, hashent);
 157                         up = new;
 158                 }
 159                 spin_unlock_bh(&uidhash_lock);
 160
 161         }
 162         return up;
 163 }
 164
 165 void switch_uid(struct user_struct *new_user)
 166 {
 167         struct user_struct *old_user;
 168
 169         /* What if a process setreuid()'s and this brings the
 170          * new uid over his NPROC rlimit?  We can check this now
 171          * cheaply with the new uid cache, so if it matters
 172          * we should be checking for it.  -DaveM
 173          */
 174         old_user = current->user;
 175         atomic_inc(&new_user->processes);
 176         atomic_dec(&old_user->processes);
 177         switch_uid_keyring(new_user);
 178         current->user = new_user;
 179         free_uid(old_user);
 180         suid_keys(current);
 181 }
 182
 183
 184 static int __init uid_cache_init(void)
 185 {
 186         int n;
 187
 188         uid_cachep = kmem_cache_create("uid_cache", sizeof(struct user_struct),
 189                         0, SLAB_HWCACHE_ALIGN|SLAB_PANIC, NULL, NULL);
 190
 191         for(n = 0; n < UIDHASH_SZ; ++n)
 192                 INIT_LIST_HEAD(uidhash_table + n);
 193
 194         /* Insert the root user immediately (init already runs as root) */
 195         spin_lock_bh(&uidhash_lock);
 196         uid_hash_insert(&root_user, uidhashentry(0));
 197         spin_unlock_bh(&uidhash_lock);
 198
 199         return 0;
 200 }
 201
 202 module_init(uid_cache_init);