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                 {
  30                         .extent[0] = {
  31                                 .first = 0,
  32                                 .lower_first = 0,
  33                                 .count = 4294967295U,
  34                         },
  35                 },
  36         },
  37         .gid_map = {
  38                 .nr_extents = 1,
  39                 {
  40                         .extent[0] = {
  41                                 .first = 0,
  42                                 .lower_first = 0,
  43                                 .count = 4294967295U,
  44                         },
  45                 },
  46         },
  47         .projid_map = {
  48                 .nr_extents = 1,
  49                 {
  50                         .extent[0] = {
  51                                 .first = 0,
  52                                 .lower_first = 0,
  53                                 .count = 4294967295U,
  54                         },
  55                 },
  56         },
  57         .count = ATOMIC_INIT(3),
  58         .owner = GLOBAL_ROOT_UID,
  59         .group = GLOBAL_ROOT_GID,
  60         .ns.inum = PROC_USER_INIT_INO,
  61 #ifdef CONFIG_USER_NS
  62         .ns.ops = &userns_operations,
  63 #endif
  64         .flags = USERNS_INIT_FLAGS,
  65 #ifdef CONFIG_PERSISTENT_KEYRINGS
  66         .persistent_keyring_register_sem =
  67         __RWSEM_INITIALIZER(init_user_ns.persistent_keyring_register_sem),
  68 #endif
  69 };
  70 EXPORT_SYMBOL_GPL(init_user_ns);
  71
  72 /*
  73  * UID task count cache, to get fast user lookup in "alloc_uid"
  74  * when changing user ID's (ie setuid() and friends).
  75  */
  76
  77 #define UIDHASH_BITS    (CONFIG_BASE_SMALL ? 3 : 7)
  78 #define UIDHASH_SZ      (1 << UIDHASH_BITS)
  79 #define UIDHASH_MASK            (UIDHASH_SZ - 1)
  80 #define __uidhashfn(uid)        (((uid >> UIDHASH_BITS) + uid) & UIDHASH_MASK)
  81 #define uidhashentry(uid)       (uidhash_table + __uidhashfn((__kuid_val(uid))))
  82
  83 static struct kmem_cache *uid_cachep;
  84 struct hlist_head uidhash_table[UIDHASH_SZ];
  85
  86 /*
  87  * The uidhash_lock is mostly taken from process context, but it is
  88  * occasionally also taken from softirq/tasklet context, when
  89  * task-structs get RCU-freed. Hence all locking must be softirq-safe.
  90  * But free_uid() is also called with local interrupts disabled, and running
  91  * local_bh_enable() with local interrupts disabled is an error - we'll run
  92  * softirq callbacks, and they can unconditionally enable interrupts, and
  93  * the caller of free_uid() didn't expect that..
  94  */
  95 static DEFINE_SPINLOCK(uidhash_lock);
  96
  97 /* root_user.__count is 1, for init task cred */
  98 struct user_struct root_user = {
  99         .__count        = ATOMIC_INIT(1),
 100         .processes      = ATOMIC_INIT(1),
 101         .sigpending     = ATOMIC_INIT(0),
 102         .locked_shm     = 0,
 103         .uid            = GLOBAL_ROOT_UID,
 104 };
 105
 106 /*
 107  * These routines must be called with the uidhash spinlock held!
 108  */
 109 static void uid_hash_insert(struct user_struct *up, struct hlist_head *hashent)
 110 {
 111         hlist_add_head(&up->uidhash_node, hashent);
 112 }
 113
 114 static void uid_hash_remove(struct user_struct *up)
 115 {
 116         hlist_del_init(&up->uidhash_node);
 117 }
 118
 119 static struct user_struct *uid_hash_find(kuid_t uid, struct hlist_head *hashent)
 120 {
 121         struct user_struct *user;
 122
 123         hlist_for_each_entry(user, hashent, uidhash_node) {
 124                 if (uid_eq(user->uid, uid)) {
 125                         atomic_inc(&user->__count);
 126                         return user;
 127                 }
 128         }
 129
 130         return NULL;
 131 }
 132
 133 /* IRQs are disabled and uidhash_lock is held upon function entry.
 134  * IRQ state (as stored in flags) is restored and uidhash_lock released
 135  * upon function exit.
 136  */
 137 static void free_user(struct user_struct *up, unsigned long flags)
 138         __releases(&uidhash_lock)
 139 {
 140         uid_hash_remove(up);
 141         spin_unlock_irqrestore(&uidhash_lock, flags);
 142         key_put(up->uid_keyring);
 143         key_put(up->session_keyring);
 144         kmem_cache_free(uid_cachep, up);
 145 }
 146
 147 /*
 148  * Locate the user_struct for the passed UID.  If found, take a ref on it.  The
 149  * caller must undo that ref with free_uid().
 150  *
 151  * If the user_struct could not be found, return NULL.
 152  */
 153 struct user_struct *find_user(kuid_t uid)
 154 {
 155         struct user_struct *ret;
 156         unsigned long flags;
 157
 158         spin_lock_irqsave(&uidhash_lock, flags);
 159         ret = uid_hash_find(uid, uidhashentry(uid));
 160         spin_unlock_irqrestore(&uidhash_lock, flags);
 161         return ret;
 162 }
 163
 164 void free_uid(struct user_struct *up)
 165 {
 166         unsigned long flags;
 167
 168         if (!up)
 169                 return;
 170
 171         local_irq_save(flags);
 172         if (atomic_dec_and_lock(&up->__count, &uidhash_lock))
 173                 free_user(up, flags);
 174         else
 175                 local_irq_restore(flags);
 176 }
 177
 178 struct user_struct *alloc_uid(kuid_t uid)
 179 {
 180         struct hlist_head *hashent = uidhashentry(uid);
 181         struct user_struct *up, *new;
 182
 183         spin_lock_irq(&uidhash_lock);
 184         up = uid_hash_find(uid, hashent);
 185         spin_unlock_irq(&uidhash_lock);
 186
 187         if (!up) {
 188                 new = kmem_cache_zalloc(uid_cachep, GFP_KERNEL);
 189                 if (!new)
 190                         goto out_unlock;
 191
 192                 new->uid = uid;
 193                 atomic_set(&new->__count, 1);
 194
 195                 /*
 196                  * Before adding this, check whether we raced
 197                  * on adding the same user already..
 198                  */
 199                 spin_lock_irq(&uidhash_lock);
 200                 up = uid_hash_find(uid, hashent);
 201                 if (up) {
 202                         key_put(new->uid_keyring);
 203                         key_put(new->session_keyring);
 204                         kmem_cache_free(uid_cachep, new);
 205                 } else {
 206                         uid_hash_insert(new, hashent);
 207                         up = new;
 208                 }
 209                 spin_unlock_irq(&uidhash_lock);
 210         }
 211
 212         return up;
 213
 214 out_unlock:
 215         return NULL;
 216 }
 217
 218 static int __init uid_cache_init(void)
 219 {
 220         int n;
 221
 222         uid_cachep = kmem_cache_create("uid_cache", sizeof(struct user_struct),
 223                         0, SLAB_HWCACHE_ALIGN|SLAB_PANIC, NULL);
 224
 225         for(n = 0; n < UIDHASH_SZ; ++n)
 226                 INIT_HLIST_HEAD(uidhash_table + n);
 227
 228         /* Insert the root user immediately (init already runs as root) */
 229         spin_lock_irq(&uidhash_lock);
 230         uid_hash_insert(&root_user, uidhashentry(GLOBAL_ROOT_UID));
 231         spin_unlock_irq(&uidhash_lock);
 232
 233         return 0;
 234 }
 235 subsys_initcall(uid_cache_init);