projects/linux·blob v2.6.25-rc1 · refs

483 lines · 11.3 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
20struct user_namespace init_user_ns = {
21 .kref = {
22 .refcount = ATOMIC_INIT(2),
23 },
24 .root_user = &root_user,
25};
26EXPORT_SYMBOL_GPL(init_user_ns);
27
28/*
29 * UID task count cache, to get fast user lookup in "alloc_uid"
30 * when changing user ID's (ie setuid() and friends).
31 */
32
33#define UIDHASH_MASK (UIDHASH_SZ - 1)
34#define __uidhashfn(uid) (((uid >> UIDHASH_BITS) + uid) & UIDHASH_MASK)
35#define uidhashentry(ns, uid) ((ns)->uidhash_table + __uidhashfn((uid)))
36
37static struct kmem_cache *uid_cachep;
38
39/*
40 * The uidhash_lock is mostly taken from process context, but it is
41 * occasionally also taken from softirq/tasklet context, when
42 * task-structs get RCU-freed. Hence all locking must be softirq-safe.
43 * But free_uid() is also called with local interrupts disabled, and running
44 * local_bh_enable() with local interrupts disabled is an error - we'll run
45 * softirq callbacks, and they can unconditionally enable interrupts, and
46 * the caller of free_uid() didn't expect that..
47 */
48static DEFINE_SPINLOCK(uidhash_lock);
49
50struct user_struct root_user = {
51 .__count = ATOMIC_INIT(1),
52 .processes = ATOMIC_INIT(1),
53 .files = ATOMIC_INIT(0),
54 .sigpending = ATOMIC_INIT(0),
55 .locked_shm = 0,
56#ifdef CONFIG_KEYS
57 .uid_keyring = &root_user_keyring,
58 .session_keyring = &root_session_keyring,
59#endif
60#ifdef CONFIG_FAIR_USER_SCHED
61 .tg = &init_task_group,
62#endif
63};
64
65/*
66 * These routines must be called with the uidhash spinlock held!
67 */
68static void uid_hash_insert(struct user_struct *up, struct hlist_head *hashent)
69{
70 hlist_add_head(&up->uidhash_node, hashent);
71}
72
73static void uid_hash_remove(struct user_struct *up)
74{
75 hlist_del_init(&up->uidhash_node);
76}
77
78static struct user_struct *uid_hash_find(uid_t uid, struct hlist_head *hashent)
79{
80 struct user_struct *user;
81 struct hlist_node *h;
82
83 hlist_for_each_entry(user, h, hashent, uidhash_node) {
84 if (user->uid == uid) {
85 atomic_inc(&user->__count);
86 return user;
87 }
88 }
89
90 return NULL;
91}
92
93#ifdef CONFIG_FAIR_USER_SCHED
94
95static void sched_destroy_user(struct user_struct *up)
96{
97 sched_destroy_group(up->tg);
98}
99
100static int sched_create_user(struct user_struct *up)
101{
102 int rc = 0;
103
104 up->tg = sched_create_group();
105 if (IS_ERR(up->tg))
106 rc = -ENOMEM;
107
108 return rc;
109}
110
111static void sched_switch_user(struct task_struct *p)
112{
113 sched_move_task(p);
114}
115
116#else /* CONFIG_FAIR_USER_SCHED */
117
118static void sched_destroy_user(struct user_struct *up) { }
119static int sched_create_user(struct user_struct *up) { return 0; }
120static void sched_switch_user(struct task_struct *p) { }
121
122#endif /* CONFIG_FAIR_USER_SCHED */
123
124#if defined(CONFIG_FAIR_USER_SCHED) && defined(CONFIG_SYSFS)
125
126static struct kset *uids_kset; /* represents the /sys/kernel/uids/ directory */
127static DEFINE_MUTEX(uids_mutex);
128
129static inline void uids_mutex_lock(void)
130{
131 mutex_lock(&uids_mutex);
132}
133
134static inline void uids_mutex_unlock(void)
135{
136 mutex_unlock(&uids_mutex);
137}
138
139/* uid directory attributes */
140static ssize_t cpu_shares_show(struct kobject *kobj,
141 struct kobj_attribute *attr,
142 char *buf)
143{
144 struct user_struct *up = container_of(kobj, struct user_struct, kobj);
145
146 return sprintf(buf, "%lu\n", sched_group_shares(up->tg));
147}
148
149static ssize_t cpu_shares_store(struct kobject *kobj,
150 struct kobj_attribute *attr,
151 const char *buf, size_t size)
152{
153 struct user_struct *up = container_of(kobj, struct user_struct, kobj);
154 unsigned long shares;
155 int rc;
156
157 sscanf(buf, "%lu", &shares);
158
159 rc = sched_group_set_shares(up->tg, shares);
160
161 return (rc ? rc : size);
162}
163
164static struct kobj_attribute cpu_share_attr =
165 __ATTR(cpu_share, 0644, cpu_shares_show, cpu_shares_store);
166
167/* default attributes per uid directory */
168static struct attribute *uids_attributes[] = {
169 &cpu_share_attr.attr,
170 NULL
171};
172
173/* the lifetime of user_struct is not managed by the core (now) */
174static void uids_release(struct kobject *kobj)
175{
176 return;
177}
178
179static struct kobj_type uids_ktype = {
180 .sysfs_ops = &kobj_sysfs_ops,
181 .default_attrs = uids_attributes,
182 .release = uids_release,
183};
184
185/* create /sys/kernel/uids/<uid>/cpu_share file for this user */
186static int uids_user_create(struct user_struct *up)
187{
188 struct kobject *kobj = &up->kobj;
189 int error;
190
191 memset(kobj, 0, sizeof(struct kobject));
192 kobj->kset = uids_kset;
193 error = kobject_init_and_add(kobj, &uids_ktype, NULL, "%d", up->uid);
194 if (error) {
195 kobject_put(kobj);
196 goto done;
197 }
198
199 kobject_uevent(kobj, KOBJ_ADD);
200done:
201 return error;
202}
203
204/* create these entries in sysfs:
205 * "/sys/kernel/uids" directory
206 * "/sys/kernel/uids/0" directory (for root user)
207 * "/sys/kernel/uids/0/cpu_share" file (for root user)
208 */
209int __init uids_sysfs_init(void)
210{
211 uids_kset = kset_create_and_add("uids", NULL, kernel_kobj);
212 if (!uids_kset)
213 return -ENOMEM;
214
215 return uids_user_create(&root_user);
216}
217
218/* work function to remove sysfs directory for a user and free up
219 * corresponding structures.
220 */
221static void remove_user_sysfs_dir(struct work_struct *w)
222{
223 struct user_struct *up = container_of(w, struct user_struct, work);
224 unsigned long flags;
225 int remove_user = 0;
226
227 /* Make uid_hash_remove() + sysfs_remove_file() + kobject_del()
228 * atomic.
229 */
230 uids_mutex_lock();
231
232 local_irq_save(flags);
233
234 if (atomic_dec_and_lock(&up->__count, &uidhash_lock)) {
235 uid_hash_remove(up);
236 remove_user = 1;
237 spin_unlock_irqrestore(&uidhash_lock, flags);
238 } else {
239 local_irq_restore(flags);
240 }
241
242 if (!remove_user)
243 goto done;
244
245 kobject_uevent(&up->kobj, KOBJ_REMOVE);
246 kobject_del(&up->kobj);
247 kobject_put(&up->kobj);
248
249 sched_destroy_user(up);
250 key_put(up->uid_keyring);
251 key_put(up->session_keyring);
252 kmem_cache_free(uid_cachep, up);
253
254done:
255 uids_mutex_unlock();
256}
257
258/* IRQs are disabled and uidhash_lock is held upon function entry.
259 * IRQ state (as stored in flags) is restored and uidhash_lock released
260 * upon function exit.
261 */
262static inline void free_user(struct user_struct *up, unsigned long flags)
263{
264 /* restore back the count */
265 atomic_inc(&up->__count);
266 spin_unlock_irqrestore(&uidhash_lock, flags);
267
268 INIT_WORK(&up->work, remove_user_sysfs_dir);
269 schedule_work(&up->work);
270}
271
272#else /* CONFIG_FAIR_USER_SCHED && CONFIG_SYSFS */
273
274int uids_sysfs_init(void) { return 0; }
275static inline int uids_user_create(struct user_struct *up) { return 0; }
276static inline void uids_mutex_lock(void) { }
277static inline void uids_mutex_unlock(void) { }
278
279/* IRQs are disabled and uidhash_lock is held upon function entry.
280 * IRQ state (as stored in flags) is restored and uidhash_lock released
281 * upon function exit.
282 */
283static inline void free_user(struct user_struct *up, unsigned long flags)
284{
285 uid_hash_remove(up);
286 spin_unlock_irqrestore(&uidhash_lock, flags);
287 sched_destroy_user(up);
288 key_put(up->uid_keyring);
289 key_put(up->session_keyring);
290 kmem_cache_free(uid_cachep, up);
291}
292
293#endif
294
295/*
296 * Locate the user_struct for the passed UID. If found, take a ref on it. The
297 * caller must undo that ref with free_uid().
298 *
299 * If the user_struct could not be found, return NULL.
300 */
301struct user_struct *find_user(uid_t uid)
302{
303 struct user_struct *ret;
304 unsigned long flags;
305 struct user_namespace *ns = current->nsproxy->user_ns;
306
307 spin_lock_irqsave(&uidhash_lock, flags);
308 ret = uid_hash_find(uid, uidhashentry(ns, uid));
309 spin_unlock_irqrestore(&uidhash_lock, flags);
310 return ret;
311}
312
313void free_uid(struct user_struct *up)
314{
315 unsigned long flags;
316
317 if (!up)
318 return;
319
320 local_irq_save(flags);
321 if (atomic_dec_and_lock(&up->__count, &uidhash_lock))
322 free_user(up, flags);
323 else
324 local_irq_restore(flags);
325}
326
327struct user_struct * alloc_uid(struct user_namespace *ns, uid_t uid)
328{
329 struct hlist_head *hashent = uidhashentry(ns, uid);
330 struct user_struct *up, *new;
331
332 /* Make uid_hash_find() + uids_user_create() + uid_hash_insert()
333 * atomic.
334 */
335 uids_mutex_lock();
336
337 spin_lock_irq(&uidhash_lock);
338 up = uid_hash_find(uid, hashent);
339 spin_unlock_irq(&uidhash_lock);
340
341 if (!up) {
342 new = kmem_cache_alloc(uid_cachep, GFP_KERNEL);
343 if (!new)
344 goto out_unlock;
345
346 new->uid = uid;
347 atomic_set(&new->__count, 1);
348 atomic_set(&new->processes, 0);
349 atomic_set(&new->files, 0);
350 atomic_set(&new->sigpending, 0);
351#ifdef CONFIG_INOTIFY_USER
352 atomic_set(&new->inotify_watches, 0);
353 atomic_set(&new->inotify_devs, 0);
354#endif
355#ifdef CONFIG_POSIX_MQUEUE
356 new->mq_bytes = 0;
357#endif
358 new->locked_shm = 0;
359
360 if (alloc_uid_keyring(new, current) < 0)
361 goto out_free_user;
362
363 if (sched_create_user(new) < 0)
364 goto out_put_keys;
365
366 if (uids_user_create(new))
367 goto out_destoy_sched;
368
369 /*
370 * Before adding this, check whether we raced
371 * on adding the same user already..
372 */
373 spin_lock_irq(&uidhash_lock);
374 up = uid_hash_find(uid, hashent);
375 if (up) {
376 /* This case is not possible when CONFIG_FAIR_USER_SCHED
377 * is defined, since we serialize alloc_uid() using
378 * uids_mutex. Hence no need to call
379 * sched_destroy_user() or remove_user_sysfs_dir().
380 */
381 key_put(new->uid_keyring);
382 key_put(new->session_keyring);
383 kmem_cache_free(uid_cachep, new);
384 } else {
385 uid_hash_insert(new, hashent);
386 up = new;
387 }
388 spin_unlock_irq(&uidhash_lock);
389
390 }
391
392 uids_mutex_unlock();
393
394 return up;
395
396out_destoy_sched:
397 sched_destroy_user(new);
398out_put_keys:
399 key_put(new->uid_keyring);
400 key_put(new->session_keyring);
401out_free_user:
402 kmem_cache_free(uid_cachep, new);
403out_unlock:
404 uids_mutex_unlock();
405 return NULL;
406}
407
408void switch_uid(struct user_struct *new_user)
409{
410 struct user_struct *old_user;
411
412 /* What if a process setreuid()'s and this brings the
413 * new uid over his NPROC rlimit? We can check this now
414 * cheaply with the new uid cache, so if it matters
415 * we should be checking for it. -DaveM
416 */
417 old_user = current->user;
418 atomic_inc(&new_user->processes);
419 atomic_dec(&old_user->processes);
420 switch_uid_keyring(new_user);
421 current->user = new_user;
422 sched_switch_user(current);
423
424 /*
425 * We need to synchronize with __sigqueue_alloc()
426 * doing a get_uid(p->user).. If that saw the old
427 * user value, we need to wait until it has exited
428 * its critical region before we can free the old
429 * structure.
430 */
431 smp_mb();
432 spin_unlock_wait(&current->sighand->siglock);
433
434 free_uid(old_user);
435 suid_keys(current);
436}
437
438#ifdef CONFIG_USER_NS
439void release_uids(struct user_namespace *ns)
440{
441 int i;
442 unsigned long flags;
443 struct hlist_head *head;
444 struct hlist_node *nd;
445
446 spin_lock_irqsave(&uidhash_lock, flags);
447 /*
448 * collapse the chains so that the user_struct-s will
449 * be still alive, but not in hashes. subsequent free_uid()
450 * will free them.
451 */
452 for (i = 0; i < UIDHASH_SZ; i++) {
453 head = ns->uidhash_table + i;
454 while (!hlist_empty(head)) {
455 nd = head->first;
456 hlist_del_init(nd);
457 }
458 }
459 spin_unlock_irqrestore(&uidhash_lock, flags);
460
461 free_uid(ns->root_user);
462}
463#endif
464
465static int __init uid_cache_init(void)
466{
467 int n;
468
469 uid_cachep = kmem_cache_create("uid_cache", sizeof(struct user_struct),
470 0, SLAB_HWCACHE_ALIGN|SLAB_PANIC, NULL);
471
472 for(n = 0; n < UIDHASH_SZ; ++n)
473 INIT_HLIST_HEAD(init_user_ns.uidhash_table + n);
474
475 /* Insert the root user immediately (init already runs as root) */
476 spin_lock_irq(&uidhash_lock);
477 uid_hash_insert(&root_user, uidhashentry(&init_user_ns, 0));
478 spin_unlock_irq(&uidhash_lock);
479
480 return 0;
481}
482
483module_init(uid_cache_init);