4 * (C) Copyright 1991-2000 Linus Torvalds
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.
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>
21 * userns count is 1 for root user, 1 for init_uts_ns,
24 struct user_namespace init_user_ns = {
26 .refcount = ATOMIC_INIT(3),
28 .owner = GLOBAL_ROOT_UID,
29 .group = GLOBAL_ROOT_GID,
31 EXPORT_SYMBOL_GPL(init_user_ns);
34 * UID task count cache, to get fast user lookup in "alloc_uid"
35 * when changing user ID's (ie setuid() and friends).
38 #define UIDHASH_BITS (CONFIG_BASE_SMALL ? 3 : 7)
39 #define UIDHASH_SZ (1 << UIDHASH_BITS)
40 #define UIDHASH_MASK (UIDHASH_SZ - 1)
41 #define __uidhashfn(uid) (((uid >> UIDHASH_BITS) + uid) & UIDHASH_MASK)
42 #define uidhashentry(uid) (uidhash_table + __uidhashfn((__kuid_val(uid))))
44 static struct kmem_cache *uid_cachep;
45 struct hlist_head uidhash_table[UIDHASH_SZ];
48 * The uidhash_lock is mostly taken from process context, but it is
49 * occasionally also taken from softirq/tasklet context, when
50 * task-structs get RCU-freed. Hence all locking must be softirq-safe.
51 * But free_uid() is also called with local interrupts disabled, and running
52 * local_bh_enable() with local interrupts disabled is an error - we'll run
53 * softirq callbacks, and they can unconditionally enable interrupts, and
54 * the caller of free_uid() didn't expect that..
56 static DEFINE_SPINLOCK(uidhash_lock);
58 /* root_user.__count is 1, for init task cred */
59 struct user_struct root_user = {
60 .__count = ATOMIC_INIT(1),
61 .processes = ATOMIC_INIT(1),
62 .files = ATOMIC_INIT(0),
63 .sigpending = ATOMIC_INIT(0),
65 .uid = GLOBAL_ROOT_UID,
69 * These routines must be called with the uidhash spinlock held!
71 static void uid_hash_insert(struct user_struct *up, struct hlist_head *hashent)
73 hlist_add_head(&up->uidhash_node, hashent);
76 static void uid_hash_remove(struct user_struct *up)
78 hlist_del_init(&up->uidhash_node);
81 static struct user_struct *uid_hash_find(kuid_t uid, struct hlist_head *hashent)
83 struct user_struct *user;
86 hlist_for_each_entry(user, h, hashent, uidhash_node) {
87 if (uid_eq(user->uid, uid)) {
88 atomic_inc(&user->__count);
96 /* IRQs are disabled and uidhash_lock is held upon function entry.
97 * IRQ state (as stored in flags) is restored and uidhash_lock released
100 static void free_user(struct user_struct *up, unsigned long flags)
101 __releases(&uidhash_lock)
104 spin_unlock_irqrestore(&uidhash_lock, flags);
105 key_put(up->uid_keyring);
106 key_put(up->session_keyring);
107 kmem_cache_free(uid_cachep, up);
111 * Locate the user_struct for the passed UID. If found, take a ref on it. The
112 * caller must undo that ref with free_uid().
114 * If the user_struct could not be found, return NULL.
116 struct user_struct *find_user(kuid_t uid)
118 struct user_struct *ret;
121 spin_lock_irqsave(&uidhash_lock, flags);
122 ret = uid_hash_find(uid, uidhashentry(uid));
123 spin_unlock_irqrestore(&uidhash_lock, flags);
127 void free_uid(struct user_struct *up)
134 local_irq_save(flags);
135 if (atomic_dec_and_lock(&up->__count, &uidhash_lock))
136 free_user(up, flags);
138 local_irq_restore(flags);
141 struct user_struct *alloc_uid(kuid_t uid)
143 struct hlist_head *hashent = uidhashentry(uid);
144 struct user_struct *up, *new;
146 spin_lock_irq(&uidhash_lock);
147 up = uid_hash_find(uid, hashent);
148 spin_unlock_irq(&uidhash_lock);
151 new = kmem_cache_zalloc(uid_cachep, GFP_KERNEL);
156 atomic_set(&new->__count, 1);
159 * Before adding this, check whether we raced
160 * on adding the same user already..
162 spin_lock_irq(&uidhash_lock);
163 up = uid_hash_find(uid, hashent);
165 key_put(new->uid_keyring);
166 key_put(new->session_keyring);
167 kmem_cache_free(uid_cachep, new);
169 uid_hash_insert(new, hashent);
172 spin_unlock_irq(&uidhash_lock);
181 static int __init uid_cache_init(void)
185 uid_cachep = kmem_cache_create("uid_cache", sizeof(struct user_struct),
186 0, SLAB_HWCACHE_ALIGN|SLAB_PANIC, NULL);
188 for(n = 0; n < UIDHASH_SZ; ++n)
189 INIT_HLIST_HEAD(uidhash_table + n);
191 /* Insert the root user immediately (init already runs as root) */
192 spin_lock_irq(&uidhash_lock);
193 uid_hash_insert(&root_user, uidhashentry(GLOBAL_ROOT_UID));
194 spin_unlock_irq(&uidhash_lock);
199 module_init(uid_cache_init);