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