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>
19 #include <linux/proc_ns.h>
22 * userns count is 1 for root user, 1 for init_uts_ns,
25 struct user_namespace init_user_ns = {
50 .count = ATOMIC_INIT(3),
51 .owner = GLOBAL_ROOT_UID,
52 .group = GLOBAL_ROOT_GID,
53 .proc_inum = PROC_USER_INIT_INO,
54 #ifdef CONFIG_PERSISTENT_KEYRINGS
55 .persistent_keyring_register_sem =
56 __RWSEM_INITIALIZER(init_user_ns.persistent_keyring_register_sem),
59 EXPORT_SYMBOL_GPL(init_user_ns);
62 * UID task count cache, to get fast user lookup in "alloc_uid"
63 * when changing user ID's (ie setuid() and friends).
66 #define UIDHASH_BITS (CONFIG_BASE_SMALL ? 3 : 7)
67 #define UIDHASH_SZ (1 << UIDHASH_BITS)
68 #define UIDHASH_MASK (UIDHASH_SZ - 1)
69 #define __uidhashfn(uid) (((uid >> UIDHASH_BITS) + uid) & UIDHASH_MASK)
70 #define uidhashentry(uid) (uidhash_table + __uidhashfn((__kuid_val(uid))))
72 static struct kmem_cache *uid_cachep;
73 struct hlist_head uidhash_table[UIDHASH_SZ];
76 * The uidhash_lock is mostly taken from process context, but it is
77 * occasionally also taken from softirq/tasklet context, when
78 * task-structs get RCU-freed. Hence all locking must be softirq-safe.
79 * But free_uid() is also called with local interrupts disabled, and running
80 * local_bh_enable() with local interrupts disabled is an error - we'll run
81 * softirq callbacks, and they can unconditionally enable interrupts, and
82 * the caller of free_uid() didn't expect that..
84 static DEFINE_SPINLOCK(uidhash_lock);
86 /* root_user.__count is 1, for init task cred */
87 struct user_struct root_user = {
88 .__count = ATOMIC_INIT(1),
89 .processes = ATOMIC_INIT(1),
90 .files = ATOMIC_INIT(0),
91 .sigpending = ATOMIC_INIT(0),
93 .uid = GLOBAL_ROOT_UID,
97 * These routines must be called with the uidhash spinlock held!
99 static void uid_hash_insert(struct user_struct *up, struct hlist_head *hashent)
101 hlist_add_head(&up->uidhash_node, hashent);
104 static void uid_hash_remove(struct user_struct *up)
106 hlist_del_init(&up->uidhash_node);
109 static struct user_struct *uid_hash_find(kuid_t uid, struct hlist_head *hashent)
111 struct user_struct *user;
113 hlist_for_each_entry(user, hashent, uidhash_node) {
114 if (uid_eq(user->uid, uid)) {
115 atomic_inc(&user->__count);
123 /* IRQs are disabled and uidhash_lock is held upon function entry.
124 * IRQ state (as stored in flags) is restored and uidhash_lock released
125 * upon function exit.
127 static void free_user(struct user_struct *up, unsigned long flags)
128 __releases(&uidhash_lock)
131 spin_unlock_irqrestore(&uidhash_lock, flags);
132 key_put(up->uid_keyring);
133 key_put(up->session_keyring);
134 kmem_cache_free(uid_cachep, up);
138 * Locate the user_struct for the passed UID. If found, take a ref on it. The
139 * caller must undo that ref with free_uid().
141 * If the user_struct could not be found, return NULL.
143 struct user_struct *find_user(kuid_t uid)
145 struct user_struct *ret;
148 spin_lock_irqsave(&uidhash_lock, flags);
149 ret = uid_hash_find(uid, uidhashentry(uid));
150 spin_unlock_irqrestore(&uidhash_lock, flags);
154 void free_uid(struct user_struct *up)
161 local_irq_save(flags);
162 if (atomic_dec_and_lock(&up->__count, &uidhash_lock))
163 free_user(up, flags);
165 local_irq_restore(flags);
168 struct user_struct *alloc_uid(kuid_t uid)
170 struct hlist_head *hashent = uidhashentry(uid);
171 struct user_struct *up, *new;
173 spin_lock_irq(&uidhash_lock);
174 up = uid_hash_find(uid, hashent);
175 spin_unlock_irq(&uidhash_lock);
178 new = kmem_cache_zalloc(uid_cachep, GFP_KERNEL);
183 atomic_set(&new->__count, 1);
186 * Before adding this, check whether we raced
187 * on adding the same user already..
189 spin_lock_irq(&uidhash_lock);
190 up = uid_hash_find(uid, hashent);
192 key_put(new->uid_keyring);
193 key_put(new->session_keyring);
194 kmem_cache_free(uid_cachep, new);
196 uid_hash_insert(new, hashent);
199 spin_unlock_irq(&uidhash_lock);
208 static int __init uid_cache_init(void)
212 uid_cachep = kmem_cache_create("uid_cache", sizeof(struct user_struct),
213 0, SLAB_HWCACHE_ALIGN|SLAB_PANIC, NULL);
215 for(n = 0; n < UIDHASH_SZ; ++n)
216 INIT_HLIST_HEAD(uidhash_table + n);
218 /* Insert the root user immediately (init already runs as root) */
219 spin_lock_irq(&uidhash_lock);
220 uid_hash_insert(&root_user, uidhashentry(GLOBAL_ROOT_UID));
221 spin_unlock_irq(&uidhash_lock);
225 subsys_initcall(uid_cache_init);