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/sched/user.h>
  17 #include <linux/interrupt.h>
  18 #include <linux/export.h>
  19 #include <linux/user_namespace.h>
  20 #include <linux/proc_ns.h>
  21
  22 /*
  23  * userns count is 1 for root user, 1 for init_uts_ns,
  24  * and 1 for... ?
  25  */
  26 struct user_namespace init_user_ns = {
  27         .uid_map = {
  28                 .nr_extents = 1,
  29                 .extent[0] = {
  30                         .first = 0,
  31                         .lower_first = 0,
  32                         .count = 4294967295U,
  33                 },
  34         },
  35         .gid_map = {
  36                 .nr_extents = 1,
  37                 .extent[0] = {
  38                         .first = 0,
  39                         .lower_first = 0,
  40                         .count = 4294967295U,
  41                 },
  42         },
  43         .projid_map = {
  44                 .nr_extents = 1,
  45                 .extent[0] = {
  46                         .first = 0,
  47                         .lower_first = 0,
  48                         .count = 4294967295U,
  49                 },
  50         },
  51         .count = ATOMIC_INIT(3),
  52         .owner = GLOBAL_ROOT_UID,
  53         .group = GLOBAL_ROOT_GID,
  54         .ns.inum = PROC_USER_INIT_INO,
  55 #ifdef CONFIG_USER_NS
  56         .ns.ops = &userns_operations,
  57 #endif
  58         .flags = USERNS_INIT_FLAGS,
  59 #ifdef CONFIG_PERSISTENT_KEYRINGS
  60         .persistent_keyring_register_sem =
  61         __RWSEM_INITIALIZER(init_user_ns.persistent_keyring_register_sem),
  62 #endif
  63 };
  64 EXPORT_SYMBOL_GPL(init_user_ns);
  65
  66 /*
  67  * UID task count cache, to get fast user lookup in "alloc_uid"
  68  * when changing user ID's (ie setuid() and friends).
  69  */
  70
  71 #define UIDHASH_BITS    (CONFIG_BASE_SMALL ? 3 : 7)
  72 #define UIDHASH_SZ      (1 << UIDHASH_BITS)
  73 #define UIDHASH_MASK            (UIDHASH_SZ - 1)
  74 #define __uidhashfn(uid)        (((uid >> UIDHASH_BITS) + uid) & UIDHASH_MASK)
  75 #define uidhashentry(uid)       (uidhash_table + __uidhashfn((__kuid_val(uid))))
  76
  77 static struct kmem_cache *uid_cachep;
  78 struct hlist_head uidhash_table[UIDHASH_SZ];
  79
  80 /*
  81  * The uidhash_lock is mostly taken from process context, but it is
  82  * occasionally also taken from softirq/tasklet context, when
  83  * task-structs get RCU-freed. Hence all locking must be softirq-safe.
  84  * But free_uid() is also called with local interrupts disabled, and running
  85  * local_bh_enable() with local interrupts disabled is an error - we'll run
  86  * softirq callbacks, and they can unconditionally enable interrupts, and
  87  * the caller of free_uid() didn't expect that..
  88  */
  89 static DEFINE_SPINLOCK(uidhash_lock);
  90
  91 /* root_user.__count is 1, for init task cred */
  92 struct user_struct root_user = {
  93         .__count        = ATOMIC_INIT(1),
  94         .processes      = ATOMIC_INIT(1),
  95         .sigpending     = ATOMIC_INIT(0),
  96         .locked_shm     = 0,
  97         .uid            = GLOBAL_ROOT_UID,
  98 };
  99
 100 /*
 101  * These routines must be called with the uidhash spinlock held!
 102  */
 103 static void uid_hash_insert(struct user_struct *up, struct hlist_head *hashent)
 104 {
 105         hlist_add_head(&up->uidhash_node, hashent);
 106 }
 107
 108 static void uid_hash_remove(struct user_struct *up)
 109 {
 110         hlist_del_init(&up->uidhash_node);
 111 }
 112
 113 static struct user_struct *uid_hash_find(kuid_t uid, struct hlist_head *hashent)
 114 {
 115         struct user_struct *user;
 116
 117         hlist_for_each_entry(user, hashent, uidhash_node) {
 118                 if (uid_eq(user->uid, uid)) {
 119                         atomic_inc(&user->__count);
 120                         return user;
 121                 }
 122         }
 123
 124         return NULL;
 125 }
 126
 127 /* IRQs are disabled and uidhash_lock is held upon function entry.
 128  * IRQ state (as stored in flags) is restored and uidhash_lock released
 129  * upon function exit.
 130  */
 131 static void free_user(struct user_struct *up, unsigned long flags)
 132         __releases(&uidhash_lock)
 133 {
 134         uid_hash_remove(up);
 135         spin_unlock_irqrestore(&uidhash_lock, flags);
 136         key_put(up->uid_keyring);
 137         key_put(up->session_keyring);
 138         kmem_cache_free(uid_cachep, up);
 139 }
 140
 141 /*
 142  * Locate the user_struct for the passed UID.  If found, take a ref on it.  The
 143  * caller must undo that ref with free_uid().
 144  *
 145  * If the user_struct could not be found, return NULL.
 146  */
 147 struct user_struct *find_user(kuid_t uid)
 148 {
 149         struct user_struct *ret;
 150         unsigned long flags;
 151
 152         spin_lock_irqsave(&uidhash_lock, flags);
 153         ret = uid_hash_find(uid, uidhashentry(uid));
 154         spin_unlock_irqrestore(&uidhash_lock, flags);
 155         return ret;
 156 }
 157
 158 void free_uid(struct user_struct *up)
 159 {
 160         unsigned long flags;
 161
 162         if (!up)
 163                 return;
 164
 165         local_irq_save(flags);
 166         if (atomic_dec_and_lock(&up->__count, &uidhash_lock))
 167                 free_user(up, flags);
 168         else
 169                 local_irq_restore(flags);
 170 }
 171
 172 struct user_struct *alloc_uid(kuid_t uid)
 173 {
 174         struct hlist_head *hashent = uidhashentry(uid);
 175         struct user_struct *up, *new;
 176
 177         spin_lock_irq(&uidhash_lock);
 178         up = uid_hash_find(uid, hashent);
 179         spin_unlock_irq(&uidhash_lock);
 180
 181         if (!up) {
 182                 new = kmem_cache_zalloc(uid_cachep, GFP_KERNEL);
 183                 if (!new)
 184                         goto out_unlock;
 185
 186                 new->uid = uid;
 187                 atomic_set(&new->__count, 1);
 188
 189                 /*
 190                  * Before adding this, check whether we raced
 191                  * on adding the same user already..
 192                  */
 193                 spin_lock_irq(&uidhash_lock);
 194                 up = uid_hash_find(uid, hashent);
 195                 if (up) {
 196                         key_put(new->uid_keyring);
 197                         key_put(new->session_keyring);
 198                         kmem_cache_free(uid_cachep, new);
 199                 } else {
 200                         uid_hash_insert(new, hashent);
 201                         up = new;
 202                 }
 203                 spin_unlock_irq(&uidhash_lock);
 204         }
 205
 206         return up;
 207
 208 out_unlock:
 209         return NULL;
 210 }
 211
 212 static int __init uid_cache_init(void)
 213 {
 214         int n;
 215
 216         uid_cachep = kmem_cache_create("uid_cache", sizeof(struct user_struct),
 217                         0, SLAB_HWCACHE_ALIGN|SLAB_PANIC, NULL);
 218
 219         for(n = 0; n < UIDHASH_SZ; ++n)
 220                 INIT_HLIST_HEAD(uidhash_table + n);
 221
 222         /* Insert the root user immediately (init already runs as root) */
 223         spin_lock_irq(&uidhash_lock);
 224         uid_hash_insert(&root_user, uidhashentry(GLOBAL_ROOT_UID));
 225         spin_unlock_irq(&uidhash_lock);
 226
 227         return 0;
 228 }
 229 subsys_initcall(uid_cache_init);