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 .ns.inum = PROC_USER_INIT_INO,
55 .ns.ops = &userns_operations,
57 .flags = USERNS_INIT_FLAGS,
58 #ifdef CONFIG_PERSISTENT_KEYRINGS
59 .persistent_keyring_register_sem =
60 __RWSEM_INITIALIZER(init_user_ns.persistent_keyring_register_sem),
63 EXPORT_SYMBOL_GPL(init_user_ns);
66 * UID task count cache, to get fast user lookup in "alloc_uid"
67 * when changing user ID's (ie setuid() and friends).
70 #define UIDHASH_BITS (CONFIG_BASE_SMALL ? 3 : 7)
71 #define UIDHASH_SZ (1 << UIDHASH_BITS)
72 #define UIDHASH_MASK (UIDHASH_SZ - 1)
73 #define __uidhashfn(uid) (((uid >> UIDHASH_BITS) + uid) & UIDHASH_MASK)
74 #define uidhashentry(uid) (uidhash_table + __uidhashfn((__kuid_val(uid))))
76 static struct kmem_cache *uid_cachep;
77 struct hlist_head uidhash_table[UIDHASH_SZ];
80 * The uidhash_lock is mostly taken from process context, but it is
81 * occasionally also taken from softirq/tasklet context, when
82 * task-structs get RCU-freed. Hence all locking must be softirq-safe.
83 * But free_uid() is also called with local interrupts disabled, and running
84 * local_bh_enable() with local interrupts disabled is an error - we'll run
85 * softirq callbacks, and they can unconditionally enable interrupts, and
86 * the caller of free_uid() didn't expect that..
88 static DEFINE_SPINLOCK(uidhash_lock);
90 /* root_user.__count is 1, for init task cred */
91 struct user_struct root_user = {
92 .__count = ATOMIC_INIT(1),
93 .processes = ATOMIC_INIT(1),
94 .sigpending = ATOMIC_INIT(0),
96 .uid = GLOBAL_ROOT_UID,
100 * These routines must be called with the uidhash spinlock held!
102 static void uid_hash_insert(struct user_struct *up, struct hlist_head *hashent)
104 hlist_add_head(&up->uidhash_node, hashent);
107 static void uid_hash_remove(struct user_struct *up)
109 hlist_del_init(&up->uidhash_node);
112 static struct user_struct *uid_hash_find(kuid_t uid, struct hlist_head *hashent)
114 struct user_struct *user;
116 hlist_for_each_entry(user, hashent, uidhash_node) {
117 if (uid_eq(user->uid, uid)) {
118 atomic_inc(&user->__count);
126 /* IRQs are disabled and uidhash_lock is held upon function entry.
127 * IRQ state (as stored in flags) is restored and uidhash_lock released
128 * upon function exit.
130 static void free_user(struct user_struct *up, unsigned long flags)
131 __releases(&uidhash_lock)
134 spin_unlock_irqrestore(&uidhash_lock, flags);
135 key_put(up->uid_keyring);
136 key_put(up->session_keyring);
137 kmem_cache_free(uid_cachep, up);
141 * Locate the user_struct for the passed UID. If found, take a ref on it. The
142 * caller must undo that ref with free_uid().
144 * If the user_struct could not be found, return NULL.
146 struct user_struct *find_user(kuid_t uid)
148 struct user_struct *ret;
151 spin_lock_irqsave(&uidhash_lock, flags);
152 ret = uid_hash_find(uid, uidhashentry(uid));
153 spin_unlock_irqrestore(&uidhash_lock, flags);
157 void free_uid(struct user_struct *up)
164 local_irq_save(flags);
165 if (atomic_dec_and_lock(&up->__count, &uidhash_lock))
166 free_user(up, flags);
168 local_irq_restore(flags);
171 struct user_struct *alloc_uid(kuid_t uid)
173 struct hlist_head *hashent = uidhashentry(uid);
174 struct user_struct *up, *new;
176 spin_lock_irq(&uidhash_lock);
177 up = uid_hash_find(uid, hashent);
178 spin_unlock_irq(&uidhash_lock);
181 new = kmem_cache_zalloc(uid_cachep, GFP_KERNEL);
186 atomic_set(&new->__count, 1);
189 * Before adding this, check whether we raced
190 * on adding the same user already..
192 spin_lock_irq(&uidhash_lock);
193 up = uid_hash_find(uid, hashent);
195 key_put(new->uid_keyring);
196 key_put(new->session_keyring);
197 kmem_cache_free(uid_cachep, new);
199 uid_hash_insert(new, hashent);
202 spin_unlock_irq(&uidhash_lock);
211 static int __init uid_cache_init(void)
215 uid_cachep = kmem_cache_create("uid_cache", sizeof(struct user_struct),
216 0, SLAB_HWCACHE_ALIGN|SLAB_PANIC, NULL);
218 for(n = 0; n < UIDHASH_SZ; ++n)
219 INIT_HLIST_HEAD(uidhash_table + n);
221 /* Insert the root user immediately (init already runs as root) */
222 spin_lock_irq(&uidhash_lock);
223 uid_hash_insert(&root_user, uidhashentry(GLOBAL_ROOT_UID));
224 spin_unlock_irq(&uidhash_lock);
228 subsys_initcall(uid_cache_init);