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