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         .ns.inum = PROC_USER_INIT_INO,
  54 #ifdef CONFIG_USER_NS
  55         .ns.ops = &userns_operations,
  56 #endif
  57         .flags = USERNS_INIT_FLAGS,
  58 #ifdef CONFIG_PERSISTENT_KEYRINGS
  59         .persistent_keyring_register_sem =
  60         __RWSEM_INITIALIZER(init_user_ns.persistent_keyring_register_sem),
  61 #endif
  62 };
  63 EXPORT_SYMBOL_GPL(init_user_ns);
  64
  65 /*
  66  * UID task count cache, to get fast user lookup in "alloc_uid"
  67  * when changing user ID's (ie setuid() and friends).
  68  */
  69
  70 #define UIDHASH_BITS    (CONFIG_BASE_SMALL ? 3 : 7)
  71 #define UIDHASH_SZ      (1 << UIDHASH_BITS)
  72 #define UIDHASH_MASK            (UIDHASH_SZ - 1)
  73 #define __uidhashfn(uid)        (((uid >> UIDHASH_BITS) + uid) & UIDHASH_MASK)
  74 #define uidhashentry(uid)       (uidhash_table + __uidhashfn((__kuid_val(uid))))
  75
  76 static struct kmem_cache *uid_cachep;
  77 struct hlist_head uidhash_table[UIDHASH_SZ];
  78
  79 /*
  80  * The uidhash_lock is mostly taken from process context, but it is
  81  * occasionally also taken from softirq/tasklet context, when
  82  * task-structs get RCU-freed. Hence all locking must be softirq-safe.
  83  * But free_uid() is also called with local interrupts disabled, and running
  84  * local_bh_enable() with local interrupts disabled is an error - we'll run
  85  * softirq callbacks, and they can unconditionally enable interrupts, and
  86  * the caller of free_uid() didn't expect that..
  87  */
  88 static DEFINE_SPINLOCK(uidhash_lock);
  89
  90 /* root_user.__count is 1, for init task cred */
  91 struct user_struct root_user = {
  92         .__count        = ATOMIC_INIT(1),
  93         .processes      = ATOMIC_INIT(1),
  94         .sigpending     = ATOMIC_INIT(0),
  95         .locked_shm     = 0,
  96         .uid            = GLOBAL_ROOT_UID,
  97 };
  98
  99 /*
 100  * These routines must be called with the uidhash spinlock held!
 101  */
 102 static void uid_hash_insert(struct user_struct *up, struct hlist_head *hashent)
 103 {
 104         hlist_add_head(&up->uidhash_node, hashent);
 105 }
 106
 107 static void uid_hash_remove(struct user_struct *up)
 108 {
 109         hlist_del_init(&up->uidhash_node);
 110 }
 111
 112 static struct user_struct *uid_hash_find(kuid_t uid, struct hlist_head *hashent)
 113 {
 114         struct user_struct *user;
 115
 116         hlist_for_each_entry(user, hashent, uidhash_node) {
 117                 if (uid_eq(user->uid, uid)) {
 118                         atomic_inc(&user->__count);
 119                         return user;
 120                 }
 121         }
 122
 123         return NULL;
 124 }
 125
 126 /* IRQs are disabled and uidhash_lock is held upon function entry.
 127  * IRQ state (as stored in flags) is restored and uidhash_lock released
 128  * upon function exit.
 129  */
 130 static void free_user(struct user_struct *up, unsigned long flags)
 131         __releases(&uidhash_lock)
 132 {
 133         uid_hash_remove(up);
 134         spin_unlock_irqrestore(&uidhash_lock, flags);
 135         key_put(up->uid_keyring);
 136         key_put(up->session_keyring);
 137         kmem_cache_free(uid_cachep, up);
 138 }
 139
 140 /*
 141  * Locate the user_struct for the passed UID.  If found, take a ref on it.  The
 142  * caller must undo that ref with free_uid().
 143  *
 144  * If the user_struct could not be found, return NULL.
 145  */
 146 struct user_struct *find_user(kuid_t uid)
 147 {
 148         struct user_struct *ret;
 149         unsigned long flags;
 150
 151         spin_lock_irqsave(&uidhash_lock, flags);
 152         ret = uid_hash_find(uid, uidhashentry(uid));
 153         spin_unlock_irqrestore(&uidhash_lock, flags);
 154         return ret;
 155 }
 156
 157 void free_uid(struct user_struct *up)
 158 {
 159         unsigned long flags;
 160
 161         if (!up)
 162                 return;
 163
 164         local_irq_save(flags);
 165         if (atomic_dec_and_lock(&up->__count, &uidhash_lock))
 166                 free_user(up, flags);
 167         else
 168                 local_irq_restore(flags);
 169 }
 170
 171 struct user_struct *alloc_uid(kuid_t uid)
 172 {
 173         struct hlist_head *hashent = uidhashentry(uid);
 174         struct user_struct *up, *new;
 175
 176         spin_lock_irq(&uidhash_lock);
 177         up = uid_hash_find(uid, hashent);
 178         spin_unlock_irq(&uidhash_lock);
 179
 180         if (!up) {
 181                 new = kmem_cache_zalloc(uid_cachep, GFP_KERNEL);
 182                 if (!new)
 183                         goto out_unlock;
 184
 185                 new->uid = uid;
 186                 atomic_set(&new->__count, 1);
 187
 188                 /*
 189                  * Before adding this, check whether we raced
 190                  * on adding the same user already..
 191                  */
 192                 spin_lock_irq(&uidhash_lock);
 193                 up = uid_hash_find(uid, hashent);
 194                 if (up) {
 195                         key_put(new->uid_keyring);
 196                         key_put(new->session_keyring);
 197                         kmem_cache_free(uid_cachep, new);
 198                 } else {
 199                         uid_hash_insert(new, hashent);
 200                         up = new;
 201                 }
 202                 spin_unlock_irq(&uidhash_lock);
 203         }
 204
 205         return up;
 206
 207 out_unlock:
 208         return NULL;
 209 }
 210
 211 static int __init uid_cache_init(void)
 212 {
 213         int n;
 214
 215         uid_cachep = kmem_cache_create("uid_cache", sizeof(struct user_struct),
 216                         0, SLAB_HWCACHE_ALIGN|SLAB_PANIC, NULL);
 217
 218         for(n = 0; n < UIDHASH_SZ; ++n)
 219                 INIT_HLIST_HEAD(uidhash_table + n);
 220
 221         /* Insert the root user immediately (init already runs as root) */
 222         spin_lock_irq(&uidhash_lock);
 223         uid_hash_insert(&root_user, uidhashentry(GLOBAL_ROOT_UID));
 224         spin_unlock_irq(&uidhash_lock);
 225
 226         return 0;
 227 }
 228 subsys_initcall(uid_cache_init);