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
  20 /*
  21  * userns count is 1 for root user, 1 for init_uts_ns,
  22  * and 1 for... ?
  23  */
  24 struct user_namespace init_user_ns = {
  25         .uid_map = {
  26                 .nr_extents = 1,
  27                 .extent[0] = {
  28                         .first = 0,
  29                         .lower_first = 0,
  30                         .count = 4294967295U,
  31                 },
  32         },
  33         .gid_map = {
  34                 .nr_extents = 1,
  35                 .extent[0] = {
  36                         .first = 0,
  37                         .lower_first = 0,
  38                         .count = 4294967295U,
  39                 },
  40         },
  41         .kref = {
  42                 .refcount       = ATOMIC_INIT(3),
  43         },
  44         .owner = GLOBAL_ROOT_UID,
  45         .group = GLOBAL_ROOT_GID,
  46 };
  47 EXPORT_SYMBOL_GPL(init_user_ns);
  48
  49 /*
  50  * UID task count cache, to get fast user lookup in "alloc_uid"
  51  * when changing user ID's (ie setuid() and friends).
  52  */
  53
  54 #define UIDHASH_BITS    (CONFIG_BASE_SMALL ? 3 : 7)
  55 #define UIDHASH_SZ      (1 << UIDHASH_BITS)
  56 #define UIDHASH_MASK            (UIDHASH_SZ - 1)
  57 #define __uidhashfn(uid)        (((uid >> UIDHASH_BITS) + uid) & UIDHASH_MASK)
  58 #define uidhashentry(uid)       (uidhash_table + __uidhashfn((__kuid_val(uid))))
  59
  60 static struct kmem_cache *uid_cachep;
  61 struct hlist_head uidhash_table[UIDHASH_SZ];
  62
  63 /*
  64  * The uidhash_lock is mostly taken from process context, but it is
  65  * occasionally also taken from softirq/tasklet context, when
  66  * task-structs get RCU-freed. Hence all locking must be softirq-safe.
  67  * But free_uid() is also called with local interrupts disabled, and running
  68  * local_bh_enable() with local interrupts disabled is an error - we'll run
  69  * softirq callbacks, and they can unconditionally enable interrupts, and
  70  * the caller of free_uid() didn't expect that..
  71  */
  72 static DEFINE_SPINLOCK(uidhash_lock);
  73
  74 /* root_user.__count is 1, for init task cred */
  75 struct user_struct root_user = {
  76         .__count        = ATOMIC_INIT(1),
  77         .processes      = ATOMIC_INIT(1),
  78         .files          = ATOMIC_INIT(0),
  79         .sigpending     = ATOMIC_INIT(0),
  80         .locked_shm     = 0,
  81         .uid            = GLOBAL_ROOT_UID,
  82 };
  83
  84 /*
  85  * These routines must be called with the uidhash spinlock held!
  86  */
  87 static void uid_hash_insert(struct user_struct *up, struct hlist_head *hashent)
  88 {
  89         hlist_add_head(&up->uidhash_node, hashent);
  90 }
  91
  92 static void uid_hash_remove(struct user_struct *up)
  93 {
  94         hlist_del_init(&up->uidhash_node);
  95 }
  96
  97 static struct user_struct *uid_hash_find(kuid_t uid, struct hlist_head *hashent)
  98 {
  99         struct user_struct *user;
 100         struct hlist_node *h;
 101
 102         hlist_for_each_entry(user, h, hashent, uidhash_node) {
 103                 if (uid_eq(user->uid, uid)) {
 104                         atomic_inc(&user->__count);
 105                         return user;
 106                 }
 107         }
 108
 109         return NULL;
 110 }
 111
 112 /* IRQs are disabled and uidhash_lock is held upon function entry.
 113  * IRQ state (as stored in flags) is restored and uidhash_lock released
 114  * upon function exit.
 115  */
 116 static void free_user(struct user_struct *up, unsigned long flags)
 117         __releases(&uidhash_lock)
 118 {
 119         uid_hash_remove(up);
 120         spin_unlock_irqrestore(&uidhash_lock, flags);
 121         key_put(up->uid_keyring);
 122         key_put(up->session_keyring);
 123         kmem_cache_free(uid_cachep, up);
 124 }
 125
 126 /*
 127  * Locate the user_struct for the passed UID.  If found, take a ref on it.  The
 128  * caller must undo that ref with free_uid().
 129  *
 130  * If the user_struct could not be found, return NULL.
 131  */
 132 struct user_struct *find_user(kuid_t uid)
 133 {
 134         struct user_struct *ret;
 135         unsigned long flags;
 136
 137         spin_lock_irqsave(&uidhash_lock, flags);
 138         ret = uid_hash_find(uid, uidhashentry(uid));
 139         spin_unlock_irqrestore(&uidhash_lock, flags);
 140         return ret;
 141 }
 142
 143 void free_uid(struct user_struct *up)
 144 {
 145         unsigned long flags;
 146
 147         if (!up)
 148                 return;
 149
 150         local_irq_save(flags);
 151         if (atomic_dec_and_lock(&up->__count, &uidhash_lock))
 152                 free_user(up, flags);
 153         else
 154                 local_irq_restore(flags);
 155 }
 156
 157 struct user_struct *alloc_uid(kuid_t uid)
 158 {
 159         struct hlist_head *hashent = uidhashentry(uid);
 160         struct user_struct *up, *new;
 161
 162         spin_lock_irq(&uidhash_lock);
 163         up = uid_hash_find(uid, hashent);
 164         spin_unlock_irq(&uidhash_lock);
 165
 166         if (!up) {
 167                 new = kmem_cache_zalloc(uid_cachep, GFP_KERNEL);
 168                 if (!new)
 169                         goto out_unlock;
 170
 171                 new->uid = uid;
 172                 atomic_set(&new->__count, 1);
 173
 174                 /*
 175                  * Before adding this, check whether we raced
 176                  * on adding the same user already..
 177                  */
 178                 spin_lock_irq(&uidhash_lock);
 179                 up = uid_hash_find(uid, hashent);
 180                 if (up) {
 181                         key_put(new->uid_keyring);
 182                         key_put(new->session_keyring);
 183                         kmem_cache_free(uid_cachep, new);
 184                 } else {
 185                         uid_hash_insert(new, hashent);
 186                         up = new;
 187                 }
 188                 spin_unlock_irq(&uidhash_lock);
 189         }
 190
 191         return up;
 192
 193 out_unlock:
 194         return NULL;
 195 }
 196
 197 static int __init uid_cache_init(void)
 198 {
 199         int n;
 200
 201         uid_cachep = kmem_cache_create("uid_cache", sizeof(struct user_struct),
 202                         0, SLAB_HWCACHE_ALIGN|SLAB_PANIC, NULL);
 203
 204         for(n = 0; n < UIDHASH_SZ; ++n)
 205                 INIT_HLIST_HEAD(uidhash_table + n);
 206
 207         /* Insert the root user immediately (init already runs as root) */
 208         spin_lock_irq(&uidhash_lock);
 209         uid_hash_insert(&root_user, uidhashentry(GLOBAL_ROOT_UID));
 210         spin_unlock_irq(&uidhash_lock);
 211
 212         return 0;
 213 }
 214
 215 module_init(uid_cache_init);