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/export.h>
18#include <linux/user_namespace.h>
19#include <linux/proc_ns.h>
20
21/*
22 * userns count is 1 for root user, 1 for init_uts_ns,
23 * and 1 for... ?
24 */
25struct user_namespace init_user_ns = {
26	.uid_map = {
27		.nr_extents = 1,
28		.extent[0] = {
29			.first = 0,
30			.lower_first = 0,
31			.count = 4294967295U,
32		},
33	},
34	.gid_map = {
35		.nr_extents = 1,
36		.extent[0] = {
37			.first = 0,
38			.lower_first = 0,
39			.count = 4294967295U,
40		},
41	},
42	.projid_map = {
43		.nr_extents = 1,
44		.extent[0] = {
45			.first = 0,
46			.lower_first = 0,
47			.count = 4294967295U,
48		},
49	},
50	.count = ATOMIC_INIT(3),
51	.owner = GLOBAL_ROOT_UID,
52	.group = GLOBAL_ROOT_GID,
53	.ns.inum = PROC_USER_INIT_INO,
54#ifdef CONFIG_USER_NS
55	.ns.ops = &userns_operations,
56#endif
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),
61#endif
62};
63EXPORT_SYMBOL_GPL(init_user_ns);
64
65/*
66 * UID task count cache, to get fast user lookup in "alloc_uid"
67 * when changing user ID's (ie setuid() and friends).
68 */
69
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))))
75
76static struct kmem_cache *uid_cachep;
77struct hlist_head uidhash_table[UIDHASH_SZ];
78
79/*
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..
87 */
88static DEFINE_SPINLOCK(uidhash_lock);
89
90/* root_user.__count is 1, for init task cred */
91struct user_struct root_user = {
92	.__count	= ATOMIC_INIT(1),
93	.processes	= ATOMIC_INIT(1),
94	.sigpending	= ATOMIC_INIT(0),
95	.locked_shm     = 0,
96	.uid		= GLOBAL_ROOT_UID,
97};
98
99/*
100 * These routines must be called with the uidhash spinlock held!
101 */
102static void uid_hash_insert(struct user_struct *up, struct hlist_head *hashent)
103{
104	hlist_add_head(&up->uidhash_node, hashent);
105}
106
107static void uid_hash_remove(struct user_struct *up)
108{
109	hlist_del_init(&up->uidhash_node);
110}
111
112static struct user_struct *uid_hash_find(kuid_t uid, struct hlist_head *hashent)
113{
114	struct user_struct *user;
115
116	hlist_for_each_entry(user, hashent, uidhash_node) {
117		if (uid_eq(user->uid, uid)) {
118			atomic_inc(&user->__count);
119			return user;
120		}
121	}
122
123	return NULL;
124}
125
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.
129 */
130static void free_user(struct user_struct *up, unsigned long flags)
131	__releases(&uidhash_lock)
132{
133	uid_hash_remove(up);
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);
138}
139
140/*
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().
143 *
144 * If the user_struct could not be found, return NULL.
145 */
146struct user_struct *find_user(kuid_t uid)
147{
148	struct user_struct *ret;
149	unsigned long flags;
150
151	spin_lock_irqsave(&uidhash_lock, flags);
152	ret = uid_hash_find(uid, uidhashentry(uid));
153	spin_unlock_irqrestore(&uidhash_lock, flags);
154	return ret;
155}
156
157void free_uid(struct user_struct *up)
158{
159	unsigned long flags;
160
161	if (!up)
162		return;
163
164	local_irq_save(flags);
165	if (atomic_dec_and_lock(&up->__count, &uidhash_lock))
166		free_user(up, flags);
167	else
168		local_irq_restore(flags);
169}
170
171struct user_struct *alloc_uid(kuid_t uid)
172{
173	struct hlist_head *hashent = uidhashentry(uid);
174	struct user_struct *up, *new;
175
176	spin_lock_irq(&uidhash_lock);
177	up = uid_hash_find(uid, hashent);
178	spin_unlock_irq(&uidhash_lock);
179
180	if (!up) {
181		new = kmem_cache_zalloc(uid_cachep, GFP_KERNEL);
182		if (!new)
183			goto out_unlock;
184
185		new->uid = uid;
186		atomic_set(&new->__count, 1);
187
188		/*
189		 * Before adding this, check whether we raced
190		 * on adding the same user already..
191		 */
192		spin_lock_irq(&uidhash_lock);
193		up = uid_hash_find(uid, hashent);
194		if (up) {
195			key_put(new->uid_keyring);
196			key_put(new->session_keyring);
197			kmem_cache_free(uid_cachep, new);
198		} else {
199			uid_hash_insert(new, hashent);
200			up = new;
201		}
202		spin_unlock_irq(&uidhash_lock);
203	}
204
205	return up;
206
207out_unlock:
208	return NULL;
209}
210
211static int __init uid_cache_init(void)
212{
213	int n;
214
215	uid_cachep = kmem_cache_create("uid_cache", sizeof(struct user_struct),
216			0, SLAB_HWCACHE_ALIGN|SLAB_PANIC, NULL);
217
218	for(n = 0; n < UIDHASH_SZ; ++n)
219		INIT_HLIST_HEAD(uidhash_table + n);
220
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);
225
226	return 0;
227}
228subsys_initcall(uid_cache_init);
229