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 #include <linux/export.h>
  18 #include <linux/user_namespace.h>
  19 #include <linux/proc_ns.h>
  20
  21 /*
  22  * userns count is 1 for root user, 1 for init_uts_ns,
  23  * and 1 for... ?
  24  */
  25 struct user_namespace init_user_ns = {
  26         .uid_map = {
  27                 .nr_extents = 1,
  28                 .extent[0] = {
  29                         .first = 0,
  30                         .lower_first = 0,
  31                         .count = 4294967295U,
  32                 },
  33         },
  34         .gid_map = {
  35                 .nr_extents = 1,
  36                 .extent[0] = {
  37                         .first = 0,
  38                         .lower_first = 0,
  39                         .count = 4294967295U,
  40                 },
  41         },
  42         .projid_map = {
  43                 .nr_extents = 1,
  44                 .extent[0] = {
  45                         .first = 0,
  46                         .lower_first = 0,
  47                         .count = 4294967295U,
  48                 },
  49         },
  50         .count = ATOMIC_INIT(3),
  51         .owner = GLOBAL_ROOT_UID,
  52         .group = GLOBAL_ROOT_GID,
  53         .proc_inum = PROC_USER_INIT_INO,
  54 };
  55 EXPORT_SYMBOL_GPL(init_user_ns);
  56
  57 /*
  58  * UID task count cache, to get fast user lookup in "alloc_uid"
  59  * when changing user ID's (ie setuid() and friends).
  60  */
  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
  68 static struct kmem_cache *uid_cachep;
  69 struct hlist_head uidhash_table[UIDHASH_SZ];
  70
  71 /*
  72  * The uidhash_lock is mostly taken from process context, but it is
  73  * occasionally also taken from softirq/tasklet context, when
  74  * task-structs get RCU-freed. Hence all locking must be softirq-safe.
  75  * But free_uid() is also called with local interrupts disabled, and running
  76  * local_bh_enable() with local interrupts disabled is an error - we'll run
  77  * softirq callbacks, and they can unconditionally enable interrupts, and
  78  * the caller of free_uid() didn't expect that..
  79  */
  80 static DEFINE_SPINLOCK(uidhash_lock);
  81
  82 /* root_user.__count is 1, for init task cred */
  83 struct user_struct root_user = {
  84         .__count        = ATOMIC_INIT(1),
  85         .processes      = ATOMIC_INIT(1),
  86         .files          = ATOMIC_INIT(0),
  87         .sigpending     = ATOMIC_INIT(0),
  88         .locked_shm     = 0,
  89         .uid            = GLOBAL_ROOT_UID,
  90 };
  91
  92 /*
  93  * These routines must be called with the uidhash spinlock held!
  94  */
  95 static void uid_hash_insert(struct user_struct *up, struct hlist_head *hashent)
  96 {
  97         hlist_add_head(&up->uidhash_node, hashent);
  98 }
  99
 100 static void uid_hash_remove(struct user_struct *up)
 101 {
 102         hlist_del_init(&up->uidhash_node);
 103 }
 104
 105 static struct user_struct *uid_hash_find(kuid_t uid, struct hlist_head *hashent)
 106 {
 107         struct user_struct *user;
 108
 109         hlist_for_each_entry(user, hashent, uidhash_node) {
 110                 if (uid_eq(user->uid, uid)) {
 111                         atomic_inc(&user->__count);
 112                         return user;
 113                 }
 114         }
 115
 116         return NULL;
 117 }
 118
 119 /* IRQs are disabled and uidhash_lock is held upon function entry.
 120  * IRQ state (as stored in flags) is restored and uidhash_lock released
 121  * upon function exit.
 122  */
 123 static void free_user(struct user_struct *up, unsigned long flags)
 124         __releases(&uidhash_lock)
 125 {
 126         uid_hash_remove(up);
 127         spin_unlock_irqrestore(&uidhash_lock, flags);
 128         key_put(up->uid_keyring);
 129         key_put(up->session_keyring);
 130         kmem_cache_free(uid_cachep, up);
 131 }
 132
 133 /*
 134  * Locate the user_struct for the passed UID.  If found, take a ref on it.  The
 135  * caller must undo that ref with free_uid().
 136  *
 137  * If the user_struct could not be found, return NULL.
 138  */
 139 struct user_struct *find_user(kuid_t uid)
 140 {
 141         struct user_struct *ret;
 142         unsigned long flags;
 143
 144         spin_lock_irqsave(&uidhash_lock, flags);
 145         ret = uid_hash_find(uid, uidhashentry(uid));
 146         spin_unlock_irqrestore(&uidhash_lock, flags);
 147         return ret;
 148 }
 149
 150 void free_uid(struct user_struct *up)
 151 {
 152         unsigned long flags;
 153
 154         if (!up)
 155                 return;
 156
 157         local_irq_save(flags);
 158         if (atomic_dec_and_lock(&up->__count, &uidhash_lock))
 159                 free_user(up, flags);
 160         else
 161                 local_irq_restore(flags);
 162 }
 163
 164 struct user_struct *alloc_uid(kuid_t uid)
 165 {
 166         struct hlist_head *hashent = uidhashentry(uid);
 167         struct user_struct *up, *new;
 168
 169         spin_lock_irq(&uidhash_lock);
 170         up = uid_hash_find(uid, hashent);
 171         spin_unlock_irq(&uidhash_lock);
 172
 173         if (!up) {
 174                 new = kmem_cache_zalloc(uid_cachep, GFP_KERNEL);
 175                 if (!new)
 176                         goto out_unlock;
 177
 178                 new->uid = uid;
 179                 atomic_set(&new->__count, 1);
 180
 181                 /*
 182                  * Before adding this, check whether we raced
 183                  * on adding the same user already..
 184                  */
 185                 spin_lock_irq(&uidhash_lock);
 186                 up = uid_hash_find(uid, hashent);
 187                 if (up) {
 188                         key_put(new->uid_keyring);
 189                         key_put(new->session_keyring);
 190                         kmem_cache_free(uid_cachep, new);
 191                 } else {
 192                         uid_hash_insert(new, hashent);
 193                         up = new;
 194                 }
 195                 spin_unlock_irq(&uidhash_lock);
 196         }
 197
 198         return up;
 199
 200 out_unlock:
 201         return NULL;
 202 }
 203
 204 static int __init uid_cache_init(void)
 205 {
 206         int n;
 207
 208         uid_cachep = kmem_cache_create("uid_cache", sizeof(struct user_struct),
 209                         0, SLAB_HWCACHE_ALIGN|SLAB_PANIC, NULL);
 210
 211         for(n = 0; n < UIDHASH_SZ; ++n)
 212                 INIT_HLIST_HEAD(uidhash_table + n);
 213
 214         /* Insert the root user immediately (init already runs as root) */
 215         spin_lock_irq(&uidhash_lock);
 216         uid_hash_insert(&root_user, uidhashentry(GLOBAL_ROOT_UID));
 217         spin_unlock_irq(&uidhash_lock);
 218
 219         return 0;
 220 }
 221
 222 module_init(uid_cache_init);