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