blob: 4869563080e9e080954d26f34b70bbffc13de18b [file] [log] [blame]
Linus Torvalds1da177e2005-04-16 15:20:36 -07001/*
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>
Ingo Molnar4021cb22006-01-25 15:23:07 +010016#include <linux/interrupt.h>
Linus Torvalds1da177e2005-04-16 15:20:36 -070017
18/*
19 * UID task count cache, to get fast user lookup in "alloc_uid"
20 * when changing user ID's (ie setuid() and friends).
21 */
22
23#define UIDHASH_BITS (CONFIG_BASE_SMALL ? 3 : 8)
24#define UIDHASH_SZ (1 << UIDHASH_BITS)
25#define UIDHASH_MASK (UIDHASH_SZ - 1)
26#define __uidhashfn(uid) (((uid >> UIDHASH_BITS) + uid) & UIDHASH_MASK)
27#define uidhashentry(uid) (uidhash_table + __uidhashfn((uid)))
28
Christoph Lametere18b8902006-12-06 20:33:20 -080029static struct kmem_cache *uid_cachep;
Linus Torvalds1da177e2005-04-16 15:20:36 -070030static struct list_head uidhash_table[UIDHASH_SZ];
Ingo Molnar4021cb22006-01-25 15:23:07 +010031
32/*
33 * The uidhash_lock is mostly taken from process context, but it is
34 * occasionally also taken from softirq/tasklet context, when
35 * task-structs get RCU-freed. Hence all locking must be softirq-safe.
Andrew Morton3fa97c92006-01-31 16:34:26 -080036 * But free_uid() is also called with local interrupts disabled, and running
37 * local_bh_enable() with local interrupts disabled is an error - we'll run
38 * softirq callbacks, and they can unconditionally enable interrupts, and
39 * the caller of free_uid() didn't expect that..
Ingo Molnar4021cb22006-01-25 15:23:07 +010040 */
Linus Torvalds1da177e2005-04-16 15:20:36 -070041static DEFINE_SPINLOCK(uidhash_lock);
42
43struct user_struct root_user = {
44 .__count = ATOMIC_INIT(1),
45 .processes = ATOMIC_INIT(1),
46 .files = ATOMIC_INIT(0),
47 .sigpending = ATOMIC_INIT(0),
48 .mq_bytes = 0,
49 .locked_shm = 0,
50#ifdef CONFIG_KEYS
51 .uid_keyring = &root_user_keyring,
52 .session_keyring = &root_session_keyring,
53#endif
54};
55
56/*
57 * These routines must be called with the uidhash spinlock held!
58 */
59static inline void uid_hash_insert(struct user_struct *up, struct list_head *hashent)
60{
61 list_add(&up->uidhash_list, hashent);
62}
63
64static inline void uid_hash_remove(struct user_struct *up)
65{
66 list_del(&up->uidhash_list);
67}
68
69static inline struct user_struct *uid_hash_find(uid_t uid, struct list_head *hashent)
70{
71 struct list_head *up;
72
73 list_for_each(up, hashent) {
74 struct user_struct *user;
75
76 user = list_entry(up, struct user_struct, uidhash_list);
77
78 if(user->uid == uid) {
79 atomic_inc(&user->__count);
80 return user;
81 }
82 }
83
84 return NULL;
85}
86
87/*
88 * Locate the user_struct for the passed UID. If found, take a ref on it. The
89 * caller must undo that ref with free_uid().
90 *
91 * If the user_struct could not be found, return NULL.
92 */
93struct user_struct *find_user(uid_t uid)
94{
95 struct user_struct *ret;
Andrew Morton3fa97c92006-01-31 16:34:26 -080096 unsigned long flags;
Linus Torvalds1da177e2005-04-16 15:20:36 -070097
Andrew Morton3fa97c92006-01-31 16:34:26 -080098 spin_lock_irqsave(&uidhash_lock, flags);
Linus Torvalds1da177e2005-04-16 15:20:36 -070099 ret = uid_hash_find(uid, uidhashentry(uid));
Andrew Morton3fa97c92006-01-31 16:34:26 -0800100 spin_unlock_irqrestore(&uidhash_lock, flags);
Linus Torvalds1da177e2005-04-16 15:20:36 -0700101 return ret;
102}
103
104void free_uid(struct user_struct *up)
105{
Andrew Morton3fa97c92006-01-31 16:34:26 -0800106 unsigned long flags;
107
Andrew Morton36f57412006-03-24 03:15:47 -0800108 if (!up)
109 return;
110
Andrew Morton3fa97c92006-01-31 16:34:26 -0800111 local_irq_save(flags);
Andrew Morton36f57412006-03-24 03:15:47 -0800112 if (atomic_dec_and_lock(&up->__count, &uidhash_lock)) {
Linus Torvalds1da177e2005-04-16 15:20:36 -0700113 uid_hash_remove(up);
Andrew Morton36f57412006-03-24 03:15:47 -0800114 spin_unlock_irqrestore(&uidhash_lock, flags);
Linus Torvalds1da177e2005-04-16 15:20:36 -0700115 key_put(up->uid_keyring);
116 key_put(up->session_keyring);
117 kmem_cache_free(uid_cachep, up);
Andrew Morton36f57412006-03-24 03:15:47 -0800118 } else {
119 local_irq_restore(flags);
Linus Torvalds1da177e2005-04-16 15:20:36 -0700120 }
121}
122
123struct user_struct * alloc_uid(uid_t uid)
124{
125 struct list_head *hashent = uidhashentry(uid);
126 struct user_struct *up;
127
Andrew Morton3fa97c92006-01-31 16:34:26 -0800128 spin_lock_irq(&uidhash_lock);
Linus Torvalds1da177e2005-04-16 15:20:36 -0700129 up = uid_hash_find(uid, hashent);
Andrew Morton3fa97c92006-01-31 16:34:26 -0800130 spin_unlock_irq(&uidhash_lock);
Linus Torvalds1da177e2005-04-16 15:20:36 -0700131
132 if (!up) {
133 struct user_struct *new;
134
Christoph Lametere94b1762006-12-06 20:33:17 -0800135 new = kmem_cache_alloc(uid_cachep, GFP_KERNEL);
Linus Torvalds1da177e2005-04-16 15:20:36 -0700136 if (!new)
137 return NULL;
138 new->uid = uid;
139 atomic_set(&new->__count, 1);
140 atomic_set(&new->processes, 0);
141 atomic_set(&new->files, 0);
142 atomic_set(&new->sigpending, 0);
Amy Griffis2d9048e2006-06-01 13:10:59 -0700143#ifdef CONFIG_INOTIFY_USER
Robert Love0eeca282005-07-12 17:06:03 -0400144 atomic_set(&new->inotify_watches, 0);
145 atomic_set(&new->inotify_devs, 0);
146#endif
Linus Torvalds1da177e2005-04-16 15:20:36 -0700147
148 new->mq_bytes = 0;
149 new->locked_shm = 0;
150
Michael LeMayd7200242006-06-22 14:47:17 -0700151 if (alloc_uid_keyring(new, current) < 0) {
Linus Torvalds1da177e2005-04-16 15:20:36 -0700152 kmem_cache_free(uid_cachep, new);
153 return NULL;
154 }
155
156 /*
157 * Before adding this, check whether we raced
158 * on adding the same user already..
159 */
Andrew Morton3fa97c92006-01-31 16:34:26 -0800160 spin_lock_irq(&uidhash_lock);
Linus Torvalds1da177e2005-04-16 15:20:36 -0700161 up = uid_hash_find(uid, hashent);
162 if (up) {
163 key_put(new->uid_keyring);
164 key_put(new->session_keyring);
165 kmem_cache_free(uid_cachep, new);
166 } else {
167 uid_hash_insert(new, hashent);
168 up = new;
169 }
Andrew Morton3fa97c92006-01-31 16:34:26 -0800170 spin_unlock_irq(&uidhash_lock);
Linus Torvalds1da177e2005-04-16 15:20:36 -0700171
172 }
173 return up;
174}
175
176void switch_uid(struct user_struct *new_user)
177{
178 struct user_struct *old_user;
179
180 /* What if a process setreuid()'s and this brings the
181 * new uid over his NPROC rlimit? We can check this now
182 * cheaply with the new uid cache, so if it matters
183 * we should be checking for it. -DaveM
184 */
185 old_user = current->user;
186 atomic_inc(&new_user->processes);
187 atomic_dec(&old_user->processes);
188 switch_uid_keyring(new_user);
189 current->user = new_user;
Linus Torvalds45c18b02006-11-04 10:06:02 -0800190
191 /*
192 * We need to synchronize with __sigqueue_alloc()
193 * doing a get_uid(p->user).. If that saw the old
194 * user value, we need to wait until it has exited
195 * its critical region before we can free the old
196 * structure.
197 */
198 smp_mb();
199 spin_unlock_wait(&current->sighand->siglock);
200
Linus Torvalds1da177e2005-04-16 15:20:36 -0700201 free_uid(old_user);
202 suid_keys(current);
203}
204
205
206static int __init uid_cache_init(void)
207{
208 int n;
209
210 uid_cachep = kmem_cache_create("uid_cache", sizeof(struct user_struct),
211 0, SLAB_HWCACHE_ALIGN|SLAB_PANIC, NULL, NULL);
212
213 for(n = 0; n < UIDHASH_SZ; ++n)
214 INIT_LIST_HEAD(uidhash_table + n);
215
216 /* Insert the root user immediately (init already runs as root) */
Andrew Morton3fa97c92006-01-31 16:34:26 -0800217 spin_lock_irq(&uidhash_lock);
Linus Torvalds1da177e2005-04-16 15:20:36 -0700218 uid_hash_insert(&root_user, uidhashentry(0));
Andrew Morton3fa97c92006-01-31 16:34:26 -0800219 spin_unlock_irq(&uidhash_lock);
Linus Torvalds1da177e2005-04-16 15:20:36 -0700220
221 return 0;
222}
223
224module_init(uid_cache_init);