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