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         .projid_map = {
  42                 .nr_extents = 1,
  43                 .extent[0] = {
  44                         .first = 0,
  45                         .lower_first = 0,
  46                         .count = 4294967295U,
  47                 },
  48         },
  49         .kref = {
  50                 .refcount       = ATOMIC_INIT(3),
  51         },
  52         .owner = GLOBAL_ROOT_UID,
  53         .group = GLOBAL_ROOT_GID,
  54 };
  55 EXPORT_SYMBOL_GPL(init_user_ns);
  56
  57 /*
  58  * UID task count cache, to get fast user lookup in "alloc_uid"
  59  * when changing user ID's (ie setuid() and friends).
  60  */
  61
  62 #define UIDHASH_BITS    (CONFIG_BASE_SMALL ? 3 : 7)
  63 #define UIDHASH_SZ      (1 << UIDHASH_BITS)
  64 #define UIDHASH_MASK            (UIDHASH_SZ - 1)
  65 #define __uidhashfn(uid)        (((uid >> UIDHASH_BITS) + uid) & UIDHASH_MASK)
  66 #define uidhashentry(uid)       (uidhash_table + __uidhashfn((__kuid_val(uid))))
  67
  68 static struct kmem_cache *uid_cachep;
  69 struct hlist_head uidhash_table[UIDHASH_SZ];
  70
  71 /*
  72  * The uidhash_lock is mostly taken from process context, but it is
  73  * occasionally also taken from softirq/tasklet context, when
  74  * task-structs get RCU-freed. Hence all locking must be softirq-safe.
  75  * But free_uid() is also called with local interrupts disabled, and running
  76  * local_bh_enable() with local interrupts disabled is an error - we'll run
  77  * softirq callbacks, and they can unconditionally enable interrupts, and
  78  * the caller of free_uid() didn't expect that..
  79  */
  80 static DEFINE_SPINLOCK(uidhash_lock);
  81
  82 /* root_user.__count is 1, for init task cred */
  83 struct user_struct root_user = {
  84         .__count        = ATOMIC_INIT(1),
  85         .processes      = ATOMIC_INIT(1),
  86         .files          = ATOMIC_INIT(0),
  87         .sigpending     = ATOMIC_INIT(0),
  88         .locked_shm     = 0,
  89         .uid            = GLOBAL_ROOT_UID,
  90 };
  91
  92 /*
  93  * These routines must be called with the uidhash spinlock held!
  94  */
  95 static void uid_hash_insert(struct user_struct *up, struct hlist_head *hashent)
  96 {
  97         hlist_add_head(&up->uidhash_node, hashent);
  98 }
  99
 100 static void uid_hash_remove(struct user_struct *up)
 101 {
 102         hlist_del_init(&up->uidhash_node);
 103 }
 104
 105 static struct user_struct *uid_hash_find(kuid_t uid, struct hlist_head *hashent)
 106 {
 107         struct user_struct *user;
 108         struct hlist_node *h;
 109
 110         hlist_for_each_entry(user, h, hashent, uidhash_node) {
 111                 if (uid_eq(user->uid, uid)) {
 112                         atomic_inc(&user->__count);
 113                         return user;
 114                 }
 115         }
 116
 117         return NULL;
 118 }
 119
 120 /* IRQs are disabled and uidhash_lock is held upon function entry.
 121  * IRQ state (as stored in flags) is restored and uidhash_lock released
 122  * upon function exit.
 123  */
 124 static void free_user(struct user_struct *up, unsigned long flags)
 125         __releases(&uidhash_lock)
 126 {
 127         uid_hash_remove(up);
 128         spin_unlock_irqrestore(&uidhash_lock, flags);
 129         key_put(up->uid_keyring);
 130         key_put(up->session_keyring);
 131         kmem_cache_free(uid_cachep, up);
 132 }
 133
 134 /*
 135  * Locate the user_struct for the passed UID.  If found, take a ref on it.  The
 136  * caller must undo that ref with free_uid().
 137  *
 138  * If the user_struct could not be found, return NULL.
 139  */
 140 struct user_struct *find_user(kuid_t uid)
 141 {
 142         struct user_struct *ret;
 143         unsigned long flags;
 144
 145         spin_lock_irqsave(&uidhash_lock, flags);
 146         ret = uid_hash_find(uid, uidhashentry(uid));
 147         spin_unlock_irqrestore(&uidhash_lock, flags);
 148         return ret;
 149 }
 150
 151 void free_uid(struct user_struct *up)
 152 {
 153         unsigned long flags;
 154
 155         if (!up)
 156                 return;
 157
 158         local_irq_save(flags);
 159         if (atomic_dec_and_lock(&up->__count, &uidhash_lock))
 160                 free_user(up, flags);
 161         else
 162                 local_irq_restore(flags);
 163 }
 164
 165 struct user_struct *alloc_uid(kuid_t uid)
 166 {
 167         struct hlist_head *hashent = uidhashentry(uid);
 168         struct user_struct *up, *new;
 169
 170         spin_lock_irq(&uidhash_lock);
 171         up = uid_hash_find(uid, hashent);
 172         spin_unlock_irq(&uidhash_lock);
 173
 174         if (!up) {
 175                 new = kmem_cache_zalloc(uid_cachep, GFP_KERNEL);
 176                 if (!new)
 177                         goto out_unlock;
 178
 179                 new->uid = uid;
 180                 atomic_set(&new->__count, 1);
 181
 182                 /*
 183                  * Before adding this, check whether we raced
 184                  * on adding the same user already..
 185                  */
 186                 spin_lock_irq(&uidhash_lock);
 187                 up = uid_hash_find(uid, hashent);
 188                 if (up) {
 189                         key_put(new->uid_keyring);
 190                         key_put(new->session_keyring);
 191                         kmem_cache_free(uid_cachep, new);
 192                 } else {
 193                         uid_hash_insert(new, hashent);
 194                         up = new;
 195                 }
 196                 spin_unlock_irq(&uidhash_lock);
 197         }
 198
 199         return up;
 200
 201 out_unlock:
 202         return NULL;
 203 }
 204
 205 static int __init uid_cache_init(void)
 206 {
 207         int n;
 208
 209         uid_cachep = kmem_cache_create("uid_cache", sizeof(struct user_struct),
 210                         0, SLAB_HWCACHE_ALIGN|SLAB_PANIC, NULL);
 211
 212         for(n = 0; n < UIDHASH_SZ; ++n)
 213                 INIT_HLIST_HEAD(uidhash_table + n);
 214
 215         /* Insert the root user immediately (init already runs as root) */
 216         spin_lock_irq(&uidhash_lock);
 217         uid_hash_insert(&root_user, uidhashentry(GLOBAL_ROOT_UID));
 218         spin_unlock_irq(&uidhash_lock);
 219
 220         return 0;
 221 }
 222
 223 module_init(uid_cache_init);