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/module.h>
  18 #include <linux/user_namespace.h>
  19
  20 /*
  21  * UID task count cache, to get fast user lookup in "alloc_uid"
  22  * when changing user ID's (ie setuid() and friends).
  23  */
  24
  25 #define UIDHASH_MASK            (UIDHASH_SZ - 1)
  26 #define __uidhashfn(uid)        (((uid >> UIDHASH_BITS) + uid) & UIDHASH_MASK)
  27 #define uidhashentry(ns, uid)   ((ns)->uidhash_table + __uidhashfn((uid)))
  28
  29 static struct kmem_cache *uid_cachep;
  30
  31 /*
  32  * The uidhash_lock is mostly taken from process context, but it is
  33  * occasionally also taken from softirq/tasklet context, when
  34  * task-structs get RCU-freed. Hence all locking must be softirq-safe.
  35  * But free_uid() is also called with local interrupts disabled, and running
  36  * local_bh_enable() with local interrupts disabled is an error - we'll run
  37  * softirq callbacks, and they can unconditionally enable interrupts, and
  38  * the caller of free_uid() didn't expect that..
  39  */
  40 static DEFINE_SPINLOCK(uidhash_lock);
  41
  42 struct user_struct root_user = {
  43         .__count        = ATOMIC_INIT(1),
  44         .processes      = ATOMIC_INIT(1),
  45         .files          = ATOMIC_INIT(0),
  46         .sigpending     = ATOMIC_INIT(0),
  47         .mq_bytes       = 0,
  48         .locked_shm     = 0,
  49 #ifdef CONFIG_KEYS
  50         .uid_keyring    = &root_user_keyring,
  51         .session_keyring = &root_session_keyring,
  52 #endif
  53 };
  54
  55 /*
  56  * These routines must be called with the uidhash spinlock held!
  57  */
  58 static inline void uid_hash_insert(struct user_struct *up, struct hlist_head *hashent)
  59 {
  60         hlist_add_head(&up->uidhash_node, hashent);
  61 }
  62
  63 static inline void uid_hash_remove(struct user_struct *up)
  64 {
  65         hlist_del_init(&up->uidhash_node);
  66 }
  67
  68 static inline struct user_struct *uid_hash_find(uid_t uid, struct hlist_head *hashent)
  69 {
  70         struct user_struct *user;
  71         struct hlist_node *h;
  72
  73         hlist_for_each_entry(user, h, hashent, uidhash_node) {
  74                 if(user->uid == uid) {
  75                         atomic_inc(&user->__count);
  76                         return user;
  77                 }
  78         }
  79
  80         return NULL;
  81 }
  82
  83 /*
  84  * Locate the user_struct for the passed UID.  If found, take a ref on it.  The
  85  * caller must undo that ref with free_uid().
  86  *
  87  * If the user_struct could not be found, return NULL.
  88  */
  89 struct user_struct *find_user(uid_t uid)
  90 {
  91         struct user_struct *ret;
  92         unsigned long flags;
  93         struct user_namespace *ns = current->nsproxy->user_ns;
  94
  95         spin_lock_irqsave(&uidhash_lock, flags);
  96         ret = uid_hash_find(uid, uidhashentry(ns, uid));
  97         spin_unlock_irqrestore(&uidhash_lock, flags);
  98         return ret;
  99 }
 100
 101 void free_uid(struct user_struct *up)
 102 {
 103         unsigned long flags;
 104
 105         if (!up)
 106                 return;
 107
 108         local_irq_save(flags);
 109         if (atomic_dec_and_lock(&up->__count, &uidhash_lock)) {
 110                 uid_hash_remove(up);
 111                 spin_unlock_irqrestore(&uidhash_lock, flags);
 112                 key_put(up->uid_keyring);
 113                 key_put(up->session_keyring);
 114                 kmem_cache_free(uid_cachep, up);
 115         } else {
 116                 local_irq_restore(flags);
 117         }
 118 }
 119
 120 struct user_struct * alloc_uid(struct user_namespace *ns, uid_t uid)
 121 {
 122         struct hlist_head *hashent = uidhashentry(ns, uid);
 123         struct user_struct *up;
 124
 125         spin_lock_irq(&uidhash_lock);
 126         up = uid_hash_find(uid, hashent);
 127         spin_unlock_irq(&uidhash_lock);
 128
 129         if (!up) {
 130                 struct user_struct *new;
 131
 132                 new = kmem_cache_alloc(uid_cachep, GFP_KERNEL);
 133                 if (!new)
 134                         return NULL;
 135                 new->uid = uid;
 136                 atomic_set(&new->__count, 1);
 137                 atomic_set(&new->processes, 0);
 138                 atomic_set(&new->files, 0);
 139                 atomic_set(&new->sigpending, 0);
 140 #ifdef CONFIG_INOTIFY_USER
 141                 atomic_set(&new->inotify_watches, 0);
 142                 atomic_set(&new->inotify_devs, 0);
 143 #endif
 144
 145                 new->mq_bytes = 0;
 146                 new->locked_shm = 0;
 147
 148                 if (alloc_uid_keyring(new, current) < 0) {
 149                         kmem_cache_free(uid_cachep, new);
 150                         return NULL;
 151                 }
 152
 153                 /*
 154                  * Before adding this, check whether we raced
 155                  * on adding the same user already..
 156                  */
 157                 spin_lock_irq(&uidhash_lock);
 158                 up = uid_hash_find(uid, hashent);
 159                 if (up) {
 160                         key_put(new->uid_keyring);
 161                         key_put(new->session_keyring);
 162                         kmem_cache_free(uid_cachep, new);
 163                 } else {
 164                         uid_hash_insert(new, hashent);
 165                         up = new;
 166                 }
 167                 spin_unlock_irq(&uidhash_lock);
 168
 169         }
 170         return up;
 171 }
 172
 173 void switch_uid(struct user_struct *new_user)
 174 {
 175         struct user_struct *old_user;
 176
 177         /* What if a process setreuid()'s and this brings the
 178          * new uid over his NPROC rlimit?  We can check this now
 179          * cheaply with the new uid cache, so if it matters
 180          * we should be checking for it.  -DaveM
 181          */
 182         old_user = current->user;
 183         atomic_inc(&new_user->processes);
 184         atomic_dec(&old_user->processes);
 185         switch_uid_keyring(new_user);
 186         current->user = new_user;
 187
 188         /*
 189          * We need to synchronize with __sigqueue_alloc()
 190          * doing a get_uid(p->user).. If that saw the old
 191          * user value, we need to wait until it has exited
 192          * its critical region before we can free the old
 193          * structure.
 194          */
 195         smp_mb();
 196         spin_unlock_wait(&current->sighand->siglock);
 197
 198         free_uid(old_user);
 199         suid_keys(current);
 200 }
 201
 202 void release_uids(struct user_namespace *ns)
 203 {
 204         int i;
 205         unsigned long flags;
 206         struct hlist_head *head;
 207         struct hlist_node *nd;
 208
 209         spin_lock_irqsave(&uidhash_lock, flags);
 210         /*
 211          * collapse the chains so that the user_struct-s will
 212          * be still alive, but not in hashes. subsequent free_uid()
 213          * will free them.
 214          */
 215         for (i = 0; i < UIDHASH_SZ; i++) {
 216                 head = ns->uidhash_table + i;
 217                 while (!hlist_empty(head)) {
 218                         nd = head->first;
 219                         hlist_del_init(nd);
 220                 }
 221         }
 222         spin_unlock_irqrestore(&uidhash_lock, flags);
 223
 224         free_uid(ns->root_user);
 225 }
 226
 227 static int __init uid_cache_init(void)
 228 {
 229         int n;
 230
 231         uid_cachep = kmem_cache_create("uid_cache", sizeof(struct user_struct),
 232                         0, SLAB_HWCACHE_ALIGN|SLAB_PANIC, NULL);
 233
 234         for(n = 0; n < UIDHASH_SZ; ++n)
 235                 INIT_HLIST_HEAD(init_user_ns.uidhash_table + n);
 236
 237         /* Insert the root user immediately (init already runs as root) */
 238         spin_lock_irq(&uidhash_lock);
 239         uid_hash_insert(&root_user, uidhashentry(&init_user_ns, 0));
 240         spin_unlock_irq(&uidhash_lock);
 241
 242         return 0;
 243 }
 244
 245 module_init(uid_cache_init);