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  * But free_uid() is also called with local interrupts disabled, and running
  37  * local_bh_enable() with local interrupts disabled is an error - we'll run
  38  * softirq callbacks, and they can unconditionally enable interrupts, and
  39  * the caller of free_uid() didn't expect that..
  40  */
  41 static DEFINE_SPINLOCK(uidhash_lock);
  42
  43 struct user_struct root_user = {
  44         .__count        = ATOMIC_INIT(1),
  45         .processes      = ATOMIC_INIT(1),
  46         .files          = ATOMIC_INIT(0),
  47         .sigpending     = ATOMIC_INIT(0),
  48         .mq_bytes       = 0,
  49         .locked_shm     = 0,
  50 #ifdef CONFIG_KEYS
  51         .uid_keyring    = &root_user_keyring,
  52         .session_keyring = &root_session_keyring,
  53 #endif
  54 };
  55
  56 /*
  57  * These routines must be called with the uidhash spinlock held!
  58  */
  59 static inline void uid_hash_insert(struct user_struct *up, struct list_head *hashent)
  60 {
  61         list_add(&up->uidhash_list, hashent);
  62 }
  63
  64 static inline void uid_hash_remove(struct user_struct *up)
  65 {
  66         list_del(&up->uidhash_list);
  67 }
  68
  69 static inline struct user_struct *uid_hash_find(uid_t uid, struct list_head *hashent)
  70 {
  71         struct list_head *up;
  72
  73         list_for_each(up, hashent) {
  74                 struct user_struct *user;
  75
  76                 user = list_entry(up, struct user_struct, uidhash_list);
  77
  78                 if(user->uid == uid) {
  79                         atomic_inc(&user->__count);
  80                         return user;
  81                 }
  82         }
  83
  84         return NULL;
  85 }
  86
  87 /*
  88  * Locate the user_struct for the passed UID.  If found, take a ref on it.  The
  89  * caller must undo that ref with free_uid().
  90  *
  91  * If the user_struct could not be found, return NULL.
  92  */
  93 struct user_struct *find_user(uid_t uid)
  94 {
  95         struct user_struct *ret;
  96         unsigned long flags;
  97
  98         spin_lock_irqsave(&uidhash_lock, flags);
  99         ret = uid_hash_find(uid, uidhashentry(uid));
 100         spin_unlock_irqrestore(&uidhash_lock, flags);
 101         return ret;
 102 }
 103
 104 void free_uid(struct user_struct *up)
 105 {
 106         unsigned long flags;
 107
 108         local_irq_save(flags);
 109         if (up && atomic_dec_and_lock(&up->__count, &uidhash_lock)) {
 110                 uid_hash_remove(up);
 111                 key_put(up->uid_keyring);
 112                 key_put(up->session_keyring);
 113                 kmem_cache_free(uid_cachep, up);
 114                 spin_unlock(&uidhash_lock);
 115         }
 116         local_irq_restore(flags);
 117 }
 118
 119 struct user_struct * alloc_uid(uid_t uid)
 120 {
 121         struct list_head *hashent = uidhashentry(uid);
 122         struct user_struct *up;
 123
 124         spin_lock_irq(&uidhash_lock);
 125         up = uid_hash_find(uid, hashent);
 126         spin_unlock_irq(&uidhash_lock);
 127
 128         if (!up) {
 129                 struct user_struct *new;
 130
 131                 new = kmem_cache_alloc(uid_cachep, SLAB_KERNEL);
 132                 if (!new)
 133                         return NULL;
 134                 new->uid = uid;
 135                 atomic_set(&new->__count, 1);
 136                 atomic_set(&new->processes, 0);
 137                 atomic_set(&new->files, 0);
 138                 atomic_set(&new->sigpending, 0);
 139 #ifdef CONFIG_INOTIFY
 140                 atomic_set(&new->inotify_watches, 0);
 141                 atomic_set(&new->inotify_devs, 0);
 142 #endif
 143
 144                 new->mq_bytes = 0;
 145                 new->locked_shm = 0;
 146
 147                 if (alloc_uid_keyring(new) < 0) {
 148                         kmem_cache_free(uid_cachep, new);
 149                         return NULL;
 150                 }
 151
 152                 /*
 153                  * Before adding this, check whether we raced
 154                  * on adding the same user already..
 155                  */
 156                 spin_lock_irq(&uidhash_lock);
 157                 up = uid_hash_find(uid, hashent);
 158                 if (up) {
 159                         key_put(new->uid_keyring);
 160                         key_put(new->session_keyring);
 161                         kmem_cache_free(uid_cachep, new);
 162                 } else {
 163                         uid_hash_insert(new, hashent);
 164                         up = new;
 165                 }
 166                 spin_unlock_irq(&uidhash_lock);
 167
 168         }
 169         return up;
 170 }
 171
 172 void switch_uid(struct user_struct *new_user)
 173 {
 174         struct user_struct *old_user;
 175
 176         /* What if a process setreuid()'s and this brings the
 177          * new uid over his NPROC rlimit?  We can check this now
 178          * cheaply with the new uid cache, so if it matters
 179          * we should be checking for it.  -DaveM
 180          */
 181         old_user = current->user;
 182         atomic_inc(&new_user->processes);
 183         atomic_dec(&old_user->processes);
 184         switch_uid_keyring(new_user);
 185         current->user = new_user;
 186         free_uid(old_user);
 187         suid_keys(current);
 188 }
 189
 190
 191 static int __init uid_cache_init(void)
 192 {
 193         int n;
 194
 195         uid_cachep = kmem_cache_create("uid_cache", sizeof(struct user_struct),
 196                         0, SLAB_HWCACHE_ALIGN|SLAB_PANIC, NULL, NULL);
 197
 198         for(n = 0; n < UIDHASH_SZ; ++n)
 199                 INIT_LIST_HEAD(uidhash_table + n);
 200
 201         /* Insert the root user immediately (init already runs as root) */
 202         spin_lock_irq(&uidhash_lock);
 203         uid_hash_insert(&root_user, uidhashentry(0));
 204         spin_unlock_irq(&uidhash_lock);
 205
 206         return 0;
 207 }
 208
 209 module_init(uid_cache_init);