projects/linux·blob v2.6.23 · refs

245 lines · 5.9 KiB

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/module.h>
18#include <linux/user_namespace.h>
19
20/*
21 * UID task count cache, to get fast user lookup in "alloc_uid"
22 * when changing user ID's (ie setuid() and friends).
23 */
24
25#define UIDHASH_MASK (UIDHASH_SZ - 1)
26#define __uidhashfn(uid) (((uid >> UIDHASH_BITS) + uid) & UIDHASH_MASK)
27#define uidhashentry(ns, uid) ((ns)->uidhash_table + __uidhashfn((uid)))
28
29static struct kmem_cache *uid_cachep;
30
31/*
32 * The uidhash_lock is mostly taken from process context, but it is
33 * occasionally also taken from softirq/tasklet context, when
34 * task-structs get RCU-freed. Hence all locking must be softirq-safe.
35 * But free_uid() is also called with local interrupts disabled, and running
36 * local_bh_enable() with local interrupts disabled is an error - we'll run
37 * softirq callbacks, and they can unconditionally enable interrupts, and
38 * the caller of free_uid() didn't expect that..
39 */
40static DEFINE_SPINLOCK(uidhash_lock);
41
42struct user_struct root_user = {
43 .__count = ATOMIC_INIT(1),
44 .processes = ATOMIC_INIT(1),
45 .files = ATOMIC_INIT(0),
46 .sigpending = ATOMIC_INIT(0),
47 .mq_bytes = 0,
48 .locked_shm = 0,
49#ifdef CONFIG_KEYS
50 .uid_keyring = &root_user_keyring,
51 .session_keyring = &root_session_keyring,
52#endif
53};
54
55/*
56 * These routines must be called with the uidhash spinlock held!
57 */
58static inline void uid_hash_insert(struct user_struct *up, struct hlist_head *hashent)
59{
60 hlist_add_head(&up->uidhash_node, hashent);
61}
62
63static inline void uid_hash_remove(struct user_struct *up)
64{
65 hlist_del_init(&up->uidhash_node);
66}
67
68static inline struct user_struct *uid_hash_find(uid_t uid, struct hlist_head *hashent)
69{
70 struct user_struct *user;
71 struct hlist_node *h;
72
73 hlist_for_each_entry(user, h, hashent, uidhash_node) {
74 if(user->uid == uid) {
75 atomic_inc(&user->__count);
76 return user;
77 }
78 }
79
80 return NULL;
81}
82
83/*
84 * Locate the user_struct for the passed UID. If found, take a ref on it. The
85 * caller must undo that ref with free_uid().
86 *
87 * If the user_struct could not be found, return NULL.
88 */
89struct user_struct *find_user(uid_t uid)
90{
91 struct user_struct *ret;
92 unsigned long flags;
93 struct user_namespace *ns = current->nsproxy->user_ns;
94
95 spin_lock_irqsave(&uidhash_lock, flags);
96 ret = uid_hash_find(uid, uidhashentry(ns, uid));
97 spin_unlock_irqrestore(&uidhash_lock, flags);
98 return ret;
99}
100
101void free_uid(struct user_struct *up)
102{
103 unsigned long flags;
104
105 if (!up)
106 return;
107
108 local_irq_save(flags);
109 if (atomic_dec_and_lock(&up->__count, &uidhash_lock)) {
110 uid_hash_remove(up);
111 spin_unlock_irqrestore(&uidhash_lock, flags);
112 key_put(up->uid_keyring);
113 key_put(up->session_keyring);
114 kmem_cache_free(uid_cachep, up);
115 } else {
116 local_irq_restore(flags);
117 }
118}
119
120struct user_struct * alloc_uid(struct user_namespace *ns, uid_t uid)
121{
122 struct hlist_head *hashent = uidhashentry(ns, uid);
123 struct user_struct *up;
124
125 spin_lock_irq(&uidhash_lock);
126 up = uid_hash_find(uid, hashent);
127 spin_unlock_irq(&uidhash_lock);
128
129 if (!up) {
130 struct user_struct *new;
131
132 new = kmem_cache_alloc(uid_cachep, GFP_KERNEL);
133 if (!new)
134 return NULL;
135 new->uid = uid;
136 atomic_set(&new->__count, 1);
137 atomic_set(&new->processes, 0);
138 atomic_set(&new->files, 0);
139 atomic_set(&new->sigpending, 0);
140#ifdef CONFIG_INOTIFY_USER
141 atomic_set(&new->inotify_watches, 0);
142 atomic_set(&new->inotify_devs, 0);
143#endif
144
145 new->mq_bytes = 0;
146 new->locked_shm = 0;
147
148 if (alloc_uid_keyring(new, current) < 0) {
149 kmem_cache_free(uid_cachep, new);
150 return NULL;
151 }
152
153 /*
154 * Before adding this, check whether we raced
155 * on adding the same user already..
156 */
157 spin_lock_irq(&uidhash_lock);
158 up = uid_hash_find(uid, hashent);
159 if (up) {
160 key_put(new->uid_keyring);
161 key_put(new->session_keyring);
162 kmem_cache_free(uid_cachep, new);
163 } else {
164 uid_hash_insert(new, hashent);
165 up = new;
166 }
167 spin_unlock_irq(&uidhash_lock);
168
169 }
170 return up;
171}
172
173void switch_uid(struct user_struct *new_user)
174{
175 struct user_struct *old_user;
176
177 /* What if a process setreuid()'s and this brings the
178 * new uid over his NPROC rlimit? We can check this now
179 * cheaply with the new uid cache, so if it matters
180 * we should be checking for it. -DaveM
181 */
182 old_user = current->user;
183 atomic_inc(&new_user->processes);
184 atomic_dec(&old_user->processes);
185 switch_uid_keyring(new_user);
186 current->user = new_user;
187
188 /*
189 * We need to synchronize with __sigqueue_alloc()
190 * doing a get_uid(p->user).. If that saw the old
191 * user value, we need to wait until it has exited
192 * its critical region before we can free the old
193 * structure.
194 */
195 smp_mb();
196 spin_unlock_wait(&current->sighand->siglock);
197
198 free_uid(old_user);
199 suid_keys(current);
200}
201
202void release_uids(struct user_namespace *ns)
203{
204 int i;
205 unsigned long flags;
206 struct hlist_head *head;
207 struct hlist_node *nd;
208
209 spin_lock_irqsave(&uidhash_lock, flags);
210 /*
211 * collapse the chains so that the user_struct-s will
212 * be still alive, but not in hashes. subsequent free_uid()
213 * will free them.
214 */
215 for (i = 0; i < UIDHASH_SZ; i++) {
216 head = ns->uidhash_table + i;
217 while (!hlist_empty(head)) {
218 nd = head->first;
219 hlist_del_init(nd);
220 }
221 }
222 spin_unlock_irqrestore(&uidhash_lock, flags);
223
224 free_uid(ns->root_user);
225}
226
227static int __init uid_cache_init(void)
228{
229 int n;
230
231 uid_cachep = kmem_cache_create("uid_cache", sizeof(struct user_struct),
232 0, SLAB_HWCACHE_ALIGN|SLAB_PANIC, NULL);
233
234 for(n = 0; n < UIDHASH_SZ; ++n)
235 INIT_HLIST_HEAD(init_user_ns.uidhash_table + n);
236
237 /* Insert the root user immediately (init already runs as root) */
238 spin_lock_irq(&uidhash_lock);
239 uid_hash_insert(&root_user, uidhashentry(&init_user_ns, 0));
240 spin_unlock_irq(&uidhash_lock);
241
242 return 0;
243}
244
245module_init(uid_cache_init);