Showing error 611

User: Jiri Slaby
Error type: Double Unlock
Error type description: Some lock is unlocked twice unintentionally in a sequence
File location: kernel/user.c
Line in file: 326
Project: Linux Kernel
Project version: 2.6.28
Tools: Stanse (1.2)
Entered: 2011-11-07 22:20:57 UTC

Source: 

  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_USER_SCHED
 57        .tg                = &init_task_group,
 58#endif
 59};
 60
 61/*
 62 * These routines must be called with the uidhash spinlock held!
 63 */
 64static void uid_hash_insert(struct user_struct *up, struct hlist_head *hashent)
 65{
 66        hlist_add_head(&up->uidhash_node, hashent);
 67}
 68
 69static void uid_hash_remove(struct user_struct *up)
 70{
 71        hlist_del_init(&up->uidhash_node);
 72}
 73
 74static struct user_struct *uid_hash_find(uid_t uid, struct hlist_head *hashent)
 75{
 76        struct user_struct *user;
 77        struct hlist_node *h;
 78
 79        hlist_for_each_entry(user, h, hashent, uidhash_node) {
 80                if (user->uid == uid) {
 81                        atomic_inc(&user->__count);
 82                        return user;
 83                }
 84        }
 85
 86        return NULL;
 87}
 88
 89#ifdef CONFIG_USER_SCHED
 90
 91static void sched_destroy_user(struct user_struct *up)
 92{
 93        sched_destroy_group(up->tg);
 94}
 95
 96static int sched_create_user(struct user_struct *up)
 97{
 98        int rc = 0;
 99
100        up->tg = sched_create_group(&root_task_group);
101        if (IS_ERR(up->tg))
102                rc = -ENOMEM;
103
104        return rc;
105}
106
107static void sched_switch_user(struct task_struct *p)
108{
109        sched_move_task(p);
110}
111
112#else        /* CONFIG_USER_SCHED */
113
114static void sched_destroy_user(struct user_struct *up) { }
115static int sched_create_user(struct user_struct *up) { return 0; }
116static void sched_switch_user(struct task_struct *p) { }
117
118#endif        /* CONFIG_USER_SCHED */
119
120#if defined(CONFIG_USER_SCHED) && defined(CONFIG_SYSFS)
121
122static struct kset *uids_kset; /* represents the /sys/kernel/uids/ directory */
123static DEFINE_MUTEX(uids_mutex);
124
125static inline void uids_mutex_lock(void)
126{
127        mutex_lock(&uids_mutex);
128}
129
130static inline void uids_mutex_unlock(void)
131{
132        mutex_unlock(&uids_mutex);
133}
134
135/* uid directory attributes */
136#ifdef CONFIG_FAIR_GROUP_SCHED
137static ssize_t cpu_shares_show(struct kobject *kobj,
138                               struct kobj_attribute *attr,
139                               char *buf)
140{
141        struct user_struct *up = container_of(kobj, struct user_struct, kobj);
142
143        return sprintf(buf, "%lu\n", sched_group_shares(up->tg));
144}
145
146static ssize_t cpu_shares_store(struct kobject *kobj,
147                                struct kobj_attribute *attr,
148                                const char *buf, size_t size)
149{
150        struct user_struct *up = container_of(kobj, struct user_struct, kobj);
151        unsigned long shares;
152        int rc;
153
154        sscanf(buf, "%lu", &shares);
155
156        rc = sched_group_set_shares(up->tg, shares);
157
158        return (rc ? rc : size);
159}
160
161static struct kobj_attribute cpu_share_attr =
162        __ATTR(cpu_share, 0644, cpu_shares_show, cpu_shares_store);
163#endif
164
165#ifdef CONFIG_RT_GROUP_SCHED
166static ssize_t cpu_rt_runtime_show(struct kobject *kobj,
167                                   struct kobj_attribute *attr,
168                                   char *buf)
169{
170        struct user_struct *up = container_of(kobj, struct user_struct, kobj);
171
172        return sprintf(buf, "%ld\n", sched_group_rt_runtime(up->tg));
173}
174
175static ssize_t cpu_rt_runtime_store(struct kobject *kobj,
176                                    struct kobj_attribute *attr,
177                                    const char *buf, size_t size)
178{
179        struct user_struct *up = container_of(kobj, struct user_struct, kobj);
180        unsigned long rt_runtime;
181        int rc;
182
183        sscanf(buf, "%ld", &rt_runtime);
184
185        rc = sched_group_set_rt_runtime(up->tg, rt_runtime);
186
187        return (rc ? rc : size);
188}
189
190static struct kobj_attribute cpu_rt_runtime_attr =
191        __ATTR(cpu_rt_runtime, 0644, cpu_rt_runtime_show, cpu_rt_runtime_store);
192
193static ssize_t cpu_rt_period_show(struct kobject *kobj,
194                                   struct kobj_attribute *attr,
195                                   char *buf)
196{
197        struct user_struct *up = container_of(kobj, struct user_struct, kobj);
198
199        return sprintf(buf, "%lu\n", sched_group_rt_period(up->tg));
200}
201
202static ssize_t cpu_rt_period_store(struct kobject *kobj,
203                                    struct kobj_attribute *attr,
204                                    const char *buf, size_t size)
205{
206        struct user_struct *up = container_of(kobj, struct user_struct, kobj);
207        unsigned long rt_period;
208        int rc;
209
210        sscanf(buf, "%lu", &rt_period);
211
212        rc = sched_group_set_rt_period(up->tg, rt_period);
213
214        return (rc ? rc : size);
215}
216
217static struct kobj_attribute cpu_rt_period_attr =
218        __ATTR(cpu_rt_period, 0644, cpu_rt_period_show, cpu_rt_period_store);
219#endif
220
221/* default attributes per uid directory */
222static struct attribute *uids_attributes[] = {
223#ifdef CONFIG_FAIR_GROUP_SCHED
224        &cpu_share_attr.attr,
225#endif
226#ifdef CONFIG_RT_GROUP_SCHED
227        &cpu_rt_runtime_attr.attr,
228        &cpu_rt_period_attr.attr,
229#endif
230        NULL
231};
232
233/* the lifetime of user_struct is not managed by the core (now) */
234static void uids_release(struct kobject *kobj)
235{
236        return;
237}
238
239static struct kobj_type uids_ktype = {
240        .sysfs_ops = &kobj_sysfs_ops,
241        .default_attrs = uids_attributes,
242        .release = uids_release,
243};
244
245/* create /sys/kernel/uids/<uid>/cpu_share file for this user */
246static int uids_user_create(struct user_struct *up)
247{
248        struct kobject *kobj = &up->kobj;
249        int error;
250
251        memset(kobj, 0, sizeof(struct kobject));
252        kobj->kset = uids_kset;
253        error = kobject_init_and_add(kobj, &uids_ktype, NULL, "%d", up->uid);
254        if (error) {
255                kobject_put(kobj);
256                goto done;
257        }
258
259        kobject_uevent(kobj, KOBJ_ADD);
260done:
261        return error;
262}
263
264/* create these entries in sysfs:
265 *         "/sys/kernel/uids" directory
266 *         "/sys/kernel/uids/0" directory (for root user)
267 *         "/sys/kernel/uids/0/cpu_share" file (for root user)
268 */
269int __init uids_sysfs_init(void)
270{
271        uids_kset = kset_create_and_add("uids", NULL, kernel_kobj);
272        if (!uids_kset)
273                return -ENOMEM;
274
275        return uids_user_create(&root_user);
276}
277
278/* work function to remove sysfs directory for a user and free up
279 * corresponding structures.
280 */
281static void remove_user_sysfs_dir(struct work_struct *w)
282{
283        struct user_struct *up = container_of(w, struct user_struct, work);
284        unsigned long flags;
285        int remove_user = 0;
286
287        /* Make uid_hash_remove() + sysfs_remove_file() + kobject_del()
288         * atomic.
289         */
290        uids_mutex_lock();
291
292        local_irq_save(flags);
293
294        if (atomic_dec_and_lock(&up->__count, &uidhash_lock)) {
295                uid_hash_remove(up);
296                remove_user = 1;
297                spin_unlock_irqrestore(&uidhash_lock, flags);
298        } else {
299                local_irq_restore(flags);
300        }
301
302        if (!remove_user)
303                goto done;
304
305        kobject_uevent(&up->kobj, KOBJ_REMOVE);
306        kobject_del(&up->kobj);
307        kobject_put(&up->kobj);
308
309        sched_destroy_user(up);
310        key_put(up->uid_keyring);
311        key_put(up->session_keyring);
312        kmem_cache_free(uid_cachep, up);
313
314done:
315        uids_mutex_unlock();
316}
317
318/* IRQs are disabled and uidhash_lock is held upon function entry.
319 * IRQ state (as stored in flags) is restored and uidhash_lock released
320 * upon function exit.
321 */
322static inline void free_user(struct user_struct *up, unsigned long flags)
323{
324        /* restore back the count */
325        atomic_inc(&up->__count);
326        spin_unlock_irqrestore(&uidhash_lock, flags);
327
328        INIT_WORK(&up->work, remove_user_sysfs_dir);
329        schedule_work(&up->work);
330}
331
332#else        /* CONFIG_USER_SCHED && CONFIG_SYSFS */
333
334int uids_sysfs_init(void) { return 0; }
335static inline int uids_user_create(struct user_struct *up) { return 0; }
336static inline void uids_mutex_lock(void) { }
337static inline void uids_mutex_unlock(void) { }
338
339/* IRQs are disabled and uidhash_lock is held upon function entry.
340 * IRQ state (as stored in flags) is restored and uidhash_lock released
341 * upon function exit.
342 */
343static inline void free_user(struct user_struct *up, unsigned long flags)
344{
345        uid_hash_remove(up);
346        spin_unlock_irqrestore(&uidhash_lock, flags);
347        sched_destroy_user(up);
348        key_put(up->uid_keyring);
349        key_put(up->session_keyring);
350        kmem_cache_free(uid_cachep, up);
351}
352
353#endif
354
355/*
356 * Locate the user_struct for the passed UID.  If found, take a ref on it.  The
357 * caller must undo that ref with free_uid().
358 *
359 * If the user_struct could not be found, return NULL.
360 */
361struct user_struct *find_user(uid_t uid)
362{
363        struct user_struct *ret;
364        unsigned long flags;
365        struct user_namespace *ns = current->nsproxy->user_ns;
366
367        spin_lock_irqsave(&uidhash_lock, flags);
368        ret = uid_hash_find(uid, uidhashentry(ns, uid));
369        spin_unlock_irqrestore(&uidhash_lock, flags);
370        return ret;
371}
372
373void free_uid(struct user_struct *up)
374{
375        unsigned long flags;
376
377        if (!up)
378                return;
379
380        local_irq_save(flags);
381        if (atomic_dec_and_lock(&up->__count, &uidhash_lock))
382                free_user(up, flags);
383        else
384                local_irq_restore(flags);
385}
386
387struct user_struct *alloc_uid(struct user_namespace *ns, uid_t uid)
388{
389        struct hlist_head *hashent = uidhashentry(ns, uid);
390        struct user_struct *up, *new;
391
392        /* Make uid_hash_find() + uids_user_create() + uid_hash_insert()
393         * atomic.
394         */
395        uids_mutex_lock();
396
397        spin_lock_irq(&uidhash_lock);
398        up = uid_hash_find(uid, hashent);
399        spin_unlock_irq(&uidhash_lock);
400
401        if (!up) {
402                new = kmem_cache_zalloc(uid_cachep, GFP_KERNEL);
403                if (!new)
404                        goto out_unlock;
405
406                new->uid = uid;
407                atomic_set(&new->__count, 1);
408
409                if (sched_create_user(new) < 0)
410                        goto out_free_user;
411
412                if (uids_user_create(new))
413                        goto out_destoy_sched;
414
415                /*
416                 * Before adding this, check whether we raced
417                 * on adding the same user already..
418                 */
419                spin_lock_irq(&uidhash_lock);
420                up = uid_hash_find(uid, hashent);
421                if (up) {
422                        /* This case is not possible when CONFIG_USER_SCHED
423                         * is defined, since we serialize alloc_uid() using
424                         * uids_mutex. Hence no need to call
425                         * sched_destroy_user() or remove_user_sysfs_dir().
426                         */
427                        key_put(new->uid_keyring);
428                        key_put(new->session_keyring);
429                        kmem_cache_free(uid_cachep, new);
430                } else {
431                        uid_hash_insert(new, hashent);
432                        up = new;
433                }
434                spin_unlock_irq(&uidhash_lock);
435
436        }
437
438        uids_mutex_unlock();
439
440        return up;
441
442out_destoy_sched:
443        sched_destroy_user(new);
444out_free_user:
445        kmem_cache_free(uid_cachep, new);
446out_unlock:
447        uids_mutex_unlock();
448        return NULL;
449}
450
451void switch_uid(struct user_struct *new_user)
452{
453        struct user_struct *old_user;
454
455        /* What if a process setreuid()'s and this brings the
456         * new uid over his NPROC rlimit?  We can check this now
457         * cheaply with the new uid cache, so if it matters
458         * we should be checking for it.  -DaveM
459         */
460        old_user = current->user;
461        atomic_inc(&new_user->processes);
462        atomic_dec(&old_user->processes);
463        switch_uid_keyring(new_user);
464        current->user = new_user;
465        sched_switch_user(current);
466
467        /*
468         * We need to synchronize with __sigqueue_alloc()
469         * doing a get_uid(p->user).. If that saw the old
470         * user value, we need to wait until it has exited
471         * its critical region before we can free the old
472         * structure.
473         */
474        smp_mb();
475        spin_unlock_wait(&current->sighand->siglock);
476
477        free_uid(old_user);
478        suid_keys(current);
479}
480
481#ifdef CONFIG_USER_NS
482void release_uids(struct user_namespace *ns)
483{
484        int i;
485        unsigned long flags;
486        struct hlist_head *head;
487        struct hlist_node *nd;
488
489        spin_lock_irqsave(&uidhash_lock, flags);
490        /*
491         * collapse the chains so that the user_struct-s will
492         * be still alive, but not in hashes. subsequent free_uid()
493         * will free them.
494         */
495        for (i = 0; i < UIDHASH_SZ; i++) {
496                head = ns->uidhash_table + i;
497                while (!hlist_empty(head)) {
498                        nd = head->first;
499                        hlist_del_init(nd);
500                }
501        }
502        spin_unlock_irqrestore(&uidhash_lock, flags);
503
504        free_uid(ns->root_user);
505}
506#endif
507
508static int __init uid_cache_init(void)
509{
510        int n;
511
512        uid_cachep = kmem_cache_create("uid_cache", sizeof(struct user_struct),
513                        0, SLAB_HWCACHE_ALIGN|SLAB_PANIC, NULL);
514
515        for(n = 0; n < UIDHASH_SZ; ++n)
516                INIT_HLIST_HEAD(init_user_ns.uidhash_table + n);
517
518        /* Insert the root user immediately (init already runs as root) */
519        spin_lock_irq(&uidhash_lock);
520        uid_hash_insert(&root_user, uidhashentry(&init_user_ns, 0));
521        spin_unlock_irq(&uidhash_lock);
522
523        return 0;
524}
525
526module_init(uid_cache_init);
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