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