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_fs.h>
  21 #include <linux/proc_ns.h>
  22
  23 /*
  24  * userns count is 1 for root user, 1 for init_uts_ns,
  25  * and 1 for... ?
  26  */
  27 struct user_namespace init_user_ns = {
  28         .uid_map = {
  29                 .nr_extents = 1,
  30                 .extent[0] = {
  31                         .first = 0,
  32                         .lower_first = 0,
  33                         .count = 4294967295U,
  34                 },
  35         },
  36         .gid_map = {
  37                 .nr_extents = 1,
  38                 .extent[0] = {
  39                         .first = 0,
  40                         .lower_first = 0,
  41                         .count = 4294967295U,
  42                 },
  43         },
  44         .projid_map = {
  45                 .nr_extents = 1,
  46                 .extent[0] = {
  47                         .first = 0,
  48                         .lower_first = 0,
  49                         .count = 4294967295U,
  50                 },
  51         },
  52         .count = ATOMIC_INIT(3),
  53         .owner = GLOBAL_ROOT_UID,
  54         .group = GLOBAL_ROOT_GID,
  55         .ns.inum = PROC_USER_INIT_INO,
  56 #ifdef CONFIG_USER_NS
  57         .ns.ops = &userns_operations,
  58 #endif
  59         .flags = USERNS_INIT_FLAGS,
  60 #ifdef CONFIG_PERSISTENT_KEYRINGS
  61         .persistent_keyring_register_sem =
  62         __RWSEM_INITIALIZER(init_user_ns.persistent_keyring_register_sem),
  63 #endif
  64 };
  65 EXPORT_SYMBOL_GPL(init_user_ns);
  66
  67 /*
  68  * UID task count cache, to get fast user lookup in "alloc_uid"
  69  * when changing user ID's (ie setuid() and friends).
  70  */
  71
  72 #define UIDHASH_BITS    (CONFIG_BASE_SMALL ? 3 : 7)
  73 #define UIDHASH_SZ      (1 << UIDHASH_BITS)
  74 #define UIDHASH_MASK            (UIDHASH_SZ - 1)
  75 #define __uidhashfn(uid)        (((uid >> UIDHASH_BITS) + uid) & UIDHASH_MASK)
  76 #define uidhashentry(uid)       (uidhash_table + __uidhashfn((__kuid_val(uid))))
  77
  78 static struct kmem_cache *uid_cachep;
  79 struct hlist_head uidhash_table[UIDHASH_SZ];
  80
  81 /*
  82  * The uidhash_lock is mostly taken from process context, but it is
  83  * occasionally also taken from softirq/tasklet context, when
  84  * task-structs get RCU-freed. Hence all locking must be softirq-safe.
  85  * But free_uid() is also called with local interrupts disabled, and running
  86  * local_bh_enable() with local interrupts disabled is an error - we'll run
  87  * softirq callbacks, and they can unconditionally enable interrupts, and
  88  * the caller of free_uid() didn't expect that..
  89  */
  90 static DEFINE_SPINLOCK(uidhash_lock);
  91
  92 /* root_user.__count is 1, for init task cred */
  93 struct user_struct root_user = {
  94         .__count        = ATOMIC_INIT(1),
  95         .processes      = ATOMIC_INIT(1),
  96         .sigpending     = ATOMIC_INIT(0),
  97         .locked_shm     = 0,
  98         .uid            = GLOBAL_ROOT_UID,
  99 };
 100
 101 /*
 102  * These routines must be called with the uidhash spinlock held!
 103  */
 104 static void uid_hash_insert(struct user_struct *up, struct hlist_head *hashent)
 105 {
 106         hlist_add_head(&up->uidhash_node, hashent);
 107 }
 108
 109 static void uid_hash_remove(struct user_struct *up)
 110 {
 111         hlist_del_init(&up->uidhash_node);
 112 }
 113
 114 static struct user_struct *uid_hash_find(kuid_t uid, struct hlist_head *hashent)
 115 {
 116         struct user_struct *user;
 117
 118         hlist_for_each_entry(user, hashent, uidhash_node) {
 119                 if (uid_eq(user->uid, uid)) {
 120                         atomic_inc(&user->__count);
 121                         return user;
 122                 }
 123         }
 124
 125         return NULL;
 126 }
 127
 128 /* IRQs are disabled and uidhash_lock is held upon function entry.
 129  * IRQ state (as stored in flags) is restored and uidhash_lock released
 130  * upon function exit.
 131  */
 132 static void free_user(struct user_struct *up, unsigned long flags)
 133         __releases(&uidhash_lock)
 134 {
 135         uid_hash_remove(up);
 136         spin_unlock_irqrestore(&uidhash_lock, flags);
 137         key_put(up->uid_keyring);
 138         key_put(up->session_keyring);
 139         kmem_cache_free(uid_cachep, up);
 140 }
 141
 142 /*
 143  * Locate the user_struct for the passed UID.  If found, take a ref on it.  The
 144  * caller must undo that ref with free_uid().
 145  *
 146  * If the user_struct could not be found, return NULL.
 147  */
 148 struct user_struct *find_user(kuid_t uid)
 149 {
 150         struct user_struct *ret;
 151         unsigned long flags;
 152
 153         spin_lock_irqsave(&uidhash_lock, flags);
 154         ret = uid_hash_find(uid, uidhashentry(uid));
 155         spin_unlock_irqrestore(&uidhash_lock, flags);
 156         return ret;
 157 }
 158
 159 void free_uid(struct user_struct *up)
 160 {
 161         unsigned long flags;
 162
 163         if (!up)
 164                 return;
 165
 166         local_irq_save(flags);
 167         if (atomic_dec_and_lock(&up->__count, &uidhash_lock))
 168                 free_user(up, flags);
 169         else
 170                 local_irq_restore(flags);
 171 }
 172
 173 struct user_struct *alloc_uid(kuid_t uid)
 174 {
 175         struct hlist_head *hashent = uidhashentry(uid);
 176         struct user_struct *up, *new;
 177
 178         spin_lock_irq(&uidhash_lock);
 179         up = uid_hash_find(uid, hashent);
 180         spin_unlock_irq(&uidhash_lock);
 181
 182         if (!up) {
 183                 new = kmem_cache_zalloc(uid_cachep, GFP_KERNEL);
 184                 if (!new)
 185                         goto out_unlock;
 186
 187                 new->uid = uid;
 188                 atomic_set(&new->__count, 1);
 189
 190                 /*
 191                  * Before adding this, check whether we raced
 192                  * on adding the same user already..
 193                  */
 194                 spin_lock_irq(&uidhash_lock);
 195                 up = uid_hash_find(uid, hashent);
 196                 if (up) {
 197                         key_put(new->uid_keyring);
 198                         key_put(new->session_keyring);
 199                         kmem_cache_free(uid_cachep, new);
 200                 } else {
 201                         uid_hash_insert(new, hashent);
 202                         up = new;
 203                 }
 204                 spin_unlock_irq(&uidhash_lock);
 205         }
 206         proc_register_uid(uid);
 207
 208         return up;
 209
 210 out_unlock:
 211         return NULL;
 212 }
 213
 214 static int __init uid_cache_init(void)
 215 {
 216         int n;
 217
 218         uid_cachep = kmem_cache_create("uid_cache", sizeof(struct user_struct),
 219                         0, SLAB_HWCACHE_ALIGN|SLAB_PANIC, NULL);
 220
 221         for(n = 0; n < UIDHASH_SZ; ++n)
 222                 INIT_HLIST_HEAD(uidhash_table + n);
 223
 224         /* Insert the root user immediately (init already runs as root) */
 225         spin_lock_irq(&uidhash_lock);
 226         uid_hash_insert(&root_user, uidhashentry(GLOBAL_ROOT_UID));
 227         spin_unlock_irq(&uidhash_lock);
 228         proc_register_uid(GLOBAL_ROOT_UID);
 229
 230         return 0;
 231 }
 232 subsys_initcall(uid_cache_init);