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 = {
50 .refcount = ATOMIC_INIT(3),
52 .owner = GLOBAL_ROOT_UID,
53 .group = GLOBAL_ROOT_GID,
55 EXPORT_SYMBOL_GPL(init_user_ns);
58 * UID task count cache, to get fast user lookup in "alloc_uid"
59 * when changing user ID's (ie setuid() and friends).
62 #define UIDHASH_BITS (CONFIG_BASE_SMALL ? 3 : 7)
63 #define UIDHASH_SZ (1 << UIDHASH_BITS)
64 #define UIDHASH_MASK (UIDHASH_SZ - 1)
65 #define __uidhashfn(uid) (((uid >> UIDHASH_BITS) + uid) & UIDHASH_MASK)
66 #define uidhashentry(uid) (uidhash_table + __uidhashfn((__kuid_val(uid))))
68 static struct kmem_cache *uid_cachep;
69 struct hlist_head uidhash_table[UIDHASH_SZ];
72 * The uidhash_lock is mostly taken from process context, but it is
73 * occasionally also taken from softirq/tasklet context, when
74 * task-structs get RCU-freed. Hence all locking must be softirq-safe.
75 * But free_uid() is also called with local interrupts disabled, and running
76 * local_bh_enable() with local interrupts disabled is an error - we'll run
77 * softirq callbacks, and they can unconditionally enable interrupts, and
78 * the caller of free_uid() didn't expect that..
80 static DEFINE_SPINLOCK(uidhash_lock);
82 /* root_user.__count is 1, for init task cred */
83 struct user_struct root_user = {
84 .__count = ATOMIC_INIT(1),
85 .processes = ATOMIC_INIT(1),
86 .files = ATOMIC_INIT(0),
87 .sigpending = ATOMIC_INIT(0),
89 .uid = GLOBAL_ROOT_UID,
93 * These routines must be called with the uidhash spinlock held!
95 static void uid_hash_insert(struct user_struct *up, struct hlist_head *hashent)
97 hlist_add_head(&up->uidhash_node, hashent);
100 static void uid_hash_remove(struct user_struct *up)
102 hlist_del_init(&up->uidhash_node);
105 static struct user_struct *uid_hash_find(kuid_t uid, struct hlist_head *hashent)
107 struct user_struct *user;
108 struct hlist_node *h;
110 hlist_for_each_entry(user, h, hashent, uidhash_node) {
111 if (uid_eq(user->uid, uid)) {
112 atomic_inc(&user->__count);
120 /* IRQs are disabled and uidhash_lock is held upon function entry.
121 * IRQ state (as stored in flags) is restored and uidhash_lock released
122 * upon function exit.
124 static void free_user(struct user_struct *up, unsigned long flags)
125 __releases(&uidhash_lock)
128 spin_unlock_irqrestore(&uidhash_lock, flags);
129 key_put(up->uid_keyring);
130 key_put(up->session_keyring);
131 kmem_cache_free(uid_cachep, up);
135 * Locate the user_struct for the passed UID. If found, take a ref on it. The
136 * caller must undo that ref with free_uid().
138 * If the user_struct could not be found, return NULL.
140 struct user_struct *find_user(kuid_t uid)
142 struct user_struct *ret;
145 spin_lock_irqsave(&uidhash_lock, flags);
146 ret = uid_hash_find(uid, uidhashentry(uid));
147 spin_unlock_irqrestore(&uidhash_lock, flags);
151 void free_uid(struct user_struct *up)
158 local_irq_save(flags);
159 if (atomic_dec_and_lock(&up->__count, &uidhash_lock))
160 free_user(up, flags);
162 local_irq_restore(flags);
165 struct user_struct *alloc_uid(kuid_t uid)
167 struct hlist_head *hashent = uidhashentry(uid);
168 struct user_struct *up, *new;
170 spin_lock_irq(&uidhash_lock);
171 up = uid_hash_find(uid, hashent);
172 spin_unlock_irq(&uidhash_lock);
175 new = kmem_cache_zalloc(uid_cachep, GFP_KERNEL);
180 atomic_set(&new->__count, 1);
183 * Before adding this, check whether we raced
184 * on adding the same user already..
186 spin_lock_irq(&uidhash_lock);
187 up = uid_hash_find(uid, hashent);
189 key_put(new->uid_keyring);
190 key_put(new->session_keyring);
191 kmem_cache_free(uid_cachep, new);
193 uid_hash_insert(new, hashent);
196 spin_unlock_irq(&uidhash_lock);
205 static int __init uid_cache_init(void)
209 uid_cachep = kmem_cache_create("uid_cache", sizeof(struct user_struct),
210 0, SLAB_HWCACHE_ALIGN|SLAB_PANIC, NULL);
212 for(n = 0; n < UIDHASH_SZ; ++n)
213 INIT_HLIST_HEAD(uidhash_table + n);
215 /* Insert the root user immediately (init already runs as root) */
216 spin_lock_irq(&uidhash_lock);
217 uid_hash_insert(&root_user, uidhashentry(GLOBAL_ROOT_UID));
218 spin_unlock_irq(&uidhash_lock);
223 module_init(uid_cache_init);