Root/kernel/user.c

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#include "cred-internals.h"
20
21struct user_namespace init_user_ns = {
22    .kref = {
23        .refcount = ATOMIC_INIT(2),
24    },
25    .creator = &root_user,
26};
27EXPORT_SYMBOL_GPL(init_user_ns);
28
29/*
30 * UID task count cache, to get fast user lookup in "alloc_uid"
31 * when changing user ID's (ie setuid() and friends).
32 */
33
34#define UIDHASH_MASK (UIDHASH_SZ - 1)
35#define __uidhashfn(uid) (((uid >> UIDHASH_BITS) + uid) & UIDHASH_MASK)
36#define uidhashentry(ns, uid) ((ns)->uidhash_table + __uidhashfn((uid)))
37
38static struct kmem_cache *uid_cachep;
39
40/*
41 * The uidhash_lock is mostly taken from process context, but it is
42 * occasionally also taken from softirq/tasklet context, when
43 * task-structs get RCU-freed. Hence all locking must be softirq-safe.
44 * But free_uid() is also called with local interrupts disabled, and running
45 * local_bh_enable() with local interrupts disabled is an error - we'll run
46 * softirq callbacks, and they can unconditionally enable interrupts, and
47 * the caller of free_uid() didn't expect that..
48 */
49static DEFINE_SPINLOCK(uidhash_lock);
50
51/* root_user.__count is 2, 1 for init task cred, 1 for init_user_ns->creator */
52struct user_struct root_user = {
53    .__count = ATOMIC_INIT(2),
54    .processes = ATOMIC_INIT(1),
55    .files = ATOMIC_INIT(0),
56    .sigpending = ATOMIC_INIT(0),
57    .locked_shm = 0,
58    .user_ns = &init_user_ns,
59#ifdef CONFIG_USER_SCHED
60    .tg = &init_task_group,
61#endif
62};
63
64/*
65 * These routines must be called with the uidhash spinlock held!
66 */
67static void uid_hash_insert(struct user_struct *up, struct hlist_head *hashent)
68{
69    hlist_add_head(&up->uidhash_node, hashent);
70}
71
72static void uid_hash_remove(struct user_struct *up)
73{
74    hlist_del_init(&up->uidhash_node);
75    put_user_ns(up->user_ns);
76}
77
78#ifdef CONFIG_USER_SCHED
79
80static void sched_destroy_user(struct user_struct *up)
81{
82    sched_destroy_group(up->tg);
83}
84
85static int sched_create_user(struct user_struct *up)
86{
87    int rc = 0;
88
89    up->tg = sched_create_group(&root_task_group);
90    if (IS_ERR(up->tg))
91        rc = -ENOMEM;
92
93    set_tg_uid(up);
94
95    return rc;
96}
97
98#else /* CONFIG_USER_SCHED */
99
100static void sched_destroy_user(struct user_struct *up) { }
101static int sched_create_user(struct user_struct *up) { return 0; }
102
103#endif /* CONFIG_USER_SCHED */
104
105#if defined(CONFIG_USER_SCHED) && defined(CONFIG_SYSFS)
106
107static struct user_struct *uid_hash_find(uid_t uid, struct hlist_head *hashent)
108{
109    struct user_struct *user;
110    struct hlist_node *h;
111
112    hlist_for_each_entry(user, h, hashent, uidhash_node) {
113        if (user->uid == uid) {
114            /* possibly resurrect an "almost deleted" object */
115            if (atomic_inc_return(&user->__count) == 1)
116                cancel_delayed_work(&user->work);
117            return user;
118        }
119    }
120
121    return NULL;
122}
123
124static struct kset *uids_kset; /* represents the /sys/kernel/uids/ directory */
125static DEFINE_MUTEX(uids_mutex);
126
127static inline void uids_mutex_lock(void)
128{
129    mutex_lock(&uids_mutex);
130}
131
132static inline void uids_mutex_unlock(void)
133{
134    mutex_unlock(&uids_mutex);
135}
136
137/* uid directory attributes */
138#ifdef CONFIG_FAIR_GROUP_SCHED
139static ssize_t cpu_shares_show(struct kobject *kobj,
140                   struct kobj_attribute *attr,
141                   char *buf)
142{
143    struct user_struct *up = container_of(kobj, struct user_struct, kobj);
144
145    return sprintf(buf, "%lu\n", sched_group_shares(up->tg));
146}
147
148static ssize_t cpu_shares_store(struct kobject *kobj,
149                struct kobj_attribute *attr,
150                const char *buf, size_t size)
151{
152    struct user_struct *up = container_of(kobj, struct user_struct, kobj);
153    unsigned long shares;
154    int rc;
155
156    sscanf(buf, "%lu", &shares);
157
158    rc = sched_group_set_shares(up->tg, shares);
159
160    return (rc ? rc : size);
161}
162
163static struct kobj_attribute cpu_share_attr =
164    __ATTR(cpu_share, 0644, cpu_shares_show, cpu_shares_store);
165#endif
166
167#ifdef CONFIG_RT_GROUP_SCHED
168static ssize_t cpu_rt_runtime_show(struct kobject *kobj,
169                   struct kobj_attribute *attr,
170                   char *buf)
171{
172    struct user_struct *up = container_of(kobj, struct user_struct, kobj);
173
174    return sprintf(buf, "%ld\n", sched_group_rt_runtime(up->tg));
175}
176
177static ssize_t cpu_rt_runtime_store(struct kobject *kobj,
178                    struct kobj_attribute *attr,
179                    const char *buf, size_t size)
180{
181    struct user_struct *up = container_of(kobj, struct user_struct, kobj);
182    unsigned long rt_runtime;
183    int rc;
184
185    sscanf(buf, "%ld", &rt_runtime);
186
187    rc = sched_group_set_rt_runtime(up->tg, rt_runtime);
188
189    return (rc ? rc : size);
190}
191
192static struct kobj_attribute cpu_rt_runtime_attr =
193    __ATTR(cpu_rt_runtime, 0644, cpu_rt_runtime_show, cpu_rt_runtime_store);
194
195static ssize_t cpu_rt_period_show(struct kobject *kobj,
196                   struct kobj_attribute *attr,
197                   char *buf)
198{
199    struct user_struct *up = container_of(kobj, struct user_struct, kobj);
200
201    return sprintf(buf, "%lu\n", sched_group_rt_period(up->tg));
202}
203
204static ssize_t cpu_rt_period_store(struct kobject *kobj,
205                    struct kobj_attribute *attr,
206                    const char *buf, size_t size)
207{
208    struct user_struct *up = container_of(kobj, struct user_struct, kobj);
209    unsigned long rt_period;
210    int rc;
211
212    sscanf(buf, "%lu", &rt_period);
213
214    rc = sched_group_set_rt_period(up->tg, rt_period);
215
216    return (rc ? rc : size);
217}
218
219static struct kobj_attribute cpu_rt_period_attr =
220    __ATTR(cpu_rt_period, 0644, cpu_rt_period_show, cpu_rt_period_store);
221#endif
222
223/* default attributes per uid directory */
224static struct attribute *uids_attributes[] = {
225#ifdef CONFIG_FAIR_GROUP_SCHED
226    &cpu_share_attr.attr,
227#endif
228#ifdef CONFIG_RT_GROUP_SCHED
229    &cpu_rt_runtime_attr.attr,
230    &cpu_rt_period_attr.attr,
231#endif
232    NULL
233};
234
235/* the lifetime of user_struct is not managed by the core (now) */
236static void uids_release(struct kobject *kobj)
237{
238    return;
239}
240
241static struct kobj_type uids_ktype = {
242    .sysfs_ops = &kobj_sysfs_ops,
243    .default_attrs = uids_attributes,
244    .release = uids_release,
245};
246
247/*
248 * Create /sys/kernel/uids/<uid>/cpu_share file for this user
249 * We do not create this file for users in a user namespace (until
250 * sysfs tagging is implemented).
251 *
252 * See Documentation/scheduler/sched-design-CFS.txt for ramifications.
253 */
254static int uids_user_create(struct user_struct *up)
255{
256    struct kobject *kobj = &up->kobj;
257    int error;
258
259    memset(kobj, 0, sizeof(struct kobject));
260    if (up->user_ns != &init_user_ns)
261        return 0;
262    kobj->kset = uids_kset;
263    error = kobject_init_and_add(kobj, &uids_ktype, NULL, "%d", up->uid);
264    if (error) {
265        kobject_put(kobj);
266        goto done;
267    }
268
269    kobject_uevent(kobj, KOBJ_ADD);
270done:
271    return error;
272}
273
274/* create these entries in sysfs:
275 * "/sys/kernel/uids" directory
276 * "/sys/kernel/uids/0" directory (for root user)
277 * "/sys/kernel/uids/0/cpu_share" file (for root user)
278 */
279int __init uids_sysfs_init(void)
280{
281    uids_kset = kset_create_and_add("uids", NULL, kernel_kobj);
282    if (!uids_kset)
283        return -ENOMEM;
284
285    return uids_user_create(&root_user);
286}
287
288/* delayed work function to remove sysfs directory for a user and free up
289 * corresponding structures.
290 */
291static void cleanup_user_struct(struct work_struct *w)
292{
293    struct user_struct *up = container_of(w, struct user_struct, work.work);
294    unsigned long flags;
295    int remove_user = 0;
296
297    /* Make uid_hash_remove() + sysfs_remove_file() + kobject_del()
298     * atomic.
299     */
300    uids_mutex_lock();
301
302    spin_lock_irqsave(&uidhash_lock, flags);
303    if (atomic_read(&up->__count) == 0) {
304        uid_hash_remove(up);
305        remove_user = 1;
306    }
307    spin_unlock_irqrestore(&uidhash_lock, flags);
308
309    if (!remove_user)
310        goto done;
311
312    if (up->user_ns == &init_user_ns) {
313        kobject_uevent(&up->kobj, KOBJ_REMOVE);
314        kobject_del(&up->kobj);
315        kobject_put(&up->kobj);
316    }
317
318    sched_destroy_user(up);
319    key_put(up->uid_keyring);
320    key_put(up->session_keyring);
321    kmem_cache_free(uid_cachep, up);
322
323done:
324    uids_mutex_unlock();
325}
326
327/* IRQs are disabled and uidhash_lock is held upon function entry.
328 * IRQ state (as stored in flags) is restored and uidhash_lock released
329 * upon function exit.
330 */
331static void free_user(struct user_struct *up, unsigned long flags)
332{
333    INIT_DELAYED_WORK(&up->work, cleanup_user_struct);
334    schedule_delayed_work(&up->work, msecs_to_jiffies(1000));
335    spin_unlock_irqrestore(&uidhash_lock, flags);
336}
337
338#else /* CONFIG_USER_SCHED && CONFIG_SYSFS */
339
340static struct user_struct *uid_hash_find(uid_t uid, struct hlist_head *hashent)
341{
342    struct user_struct *user;
343    struct hlist_node *h;
344
345    hlist_for_each_entry(user, h, hashent, uidhash_node) {
346        if (user->uid == uid) {
347            atomic_inc(&user->__count);
348            return user;
349        }
350    }
351
352    return NULL;
353}
354
355int uids_sysfs_init(void) { return 0; }
356static inline int uids_user_create(struct user_struct *up) { return 0; }
357static inline void uids_mutex_lock(void) { }
358static inline void uids_mutex_unlock(void) { }
359
360/* IRQs are disabled and uidhash_lock is held upon function entry.
361 * IRQ state (as stored in flags) is restored and uidhash_lock released
362 * upon function exit.
363 */
364static void free_user(struct user_struct *up, unsigned long flags)
365{
366    uid_hash_remove(up);
367    spin_unlock_irqrestore(&uidhash_lock, flags);
368    sched_destroy_user(up);
369    key_put(up->uid_keyring);
370    key_put(up->session_keyring);
371    kmem_cache_free(uid_cachep, up);
372}
373
374#endif
375
376#if defined(CONFIG_RT_GROUP_SCHED) && defined(CONFIG_USER_SCHED)
377/*
378 * We need to check if a setuid can take place. This function should be called
379 * before successfully completing the setuid.
380 */
381int task_can_switch_user(struct user_struct *up, struct task_struct *tsk)
382{
383
384    return sched_rt_can_attach(up->tg, tsk);
385
386}
387#else
388int task_can_switch_user(struct user_struct *up, struct task_struct *tsk)
389{
390    return 1;
391}
392#endif
393
394/*
395 * Locate the user_struct for the passed UID. If found, take a ref on it. The
396 * caller must undo that ref with free_uid().
397 *
398 * If the user_struct could not be found, return NULL.
399 */
400struct user_struct *find_user(uid_t uid)
401{
402    struct user_struct *ret;
403    unsigned long flags;
404    struct user_namespace *ns = current_user_ns();
405
406    spin_lock_irqsave(&uidhash_lock, flags);
407    ret = uid_hash_find(uid, uidhashentry(ns, uid));
408    spin_unlock_irqrestore(&uidhash_lock, flags);
409    return ret;
410}
411
412void free_uid(struct user_struct *up)
413{
414    unsigned long flags;
415
416    if (!up)
417        return;
418
419    local_irq_save(flags);
420    if (atomic_dec_and_lock(&up->__count, &uidhash_lock))
421        free_user(up, flags);
422    else
423        local_irq_restore(flags);
424}
425
426struct user_struct *alloc_uid(struct user_namespace *ns, uid_t uid)
427{
428    struct hlist_head *hashent = uidhashentry(ns, uid);
429    struct user_struct *up, *new;
430
431    /* Make uid_hash_find() + uids_user_create() + uid_hash_insert()
432     * atomic.
433     */
434    uids_mutex_lock();
435
436    spin_lock_irq(&uidhash_lock);
437    up = uid_hash_find(uid, hashent);
438    spin_unlock_irq(&uidhash_lock);
439
440    if (!up) {
441        new = kmem_cache_zalloc(uid_cachep, GFP_KERNEL);
442        if (!new)
443            goto out_unlock;
444
445        new->uid = uid;
446        atomic_set(&new->__count, 1);
447
448        if (sched_create_user(new) < 0)
449            goto out_free_user;
450
451        new->user_ns = get_user_ns(ns);
452
453        if (uids_user_create(new))
454            goto out_destoy_sched;
455
456        /*
457         * Before adding this, check whether we raced
458         * on adding the same user already..
459         */
460        spin_lock_irq(&uidhash_lock);
461        up = uid_hash_find(uid, hashent);
462        if (up) {
463            /* This case is not possible when CONFIG_USER_SCHED
464             * is defined, since we serialize alloc_uid() using
465             * uids_mutex. Hence no need to call
466             * sched_destroy_user() or remove_user_sysfs_dir().
467             */
468            key_put(new->uid_keyring);
469            key_put(new->session_keyring);
470            kmem_cache_free(uid_cachep, new);
471        } else {
472            uid_hash_insert(new, hashent);
473            up = new;
474        }
475        spin_unlock_irq(&uidhash_lock);
476    }
477
478    uids_mutex_unlock();
479
480    return up;
481
482out_destoy_sched:
483    sched_destroy_user(new);
484    put_user_ns(new->user_ns);
485out_free_user:
486    kmem_cache_free(uid_cachep, new);
487out_unlock:
488    uids_mutex_unlock();
489    return NULL;
490}
491
492static int __init uid_cache_init(void)
493{
494    int n;
495
496    uid_cachep = kmem_cache_create("uid_cache", sizeof(struct user_struct),
497            0, SLAB_HWCACHE_ALIGN|SLAB_PANIC, NULL);
498
499    for(n = 0; n < UIDHASH_SZ; ++n)
500        INIT_HLIST_HEAD(init_user_ns.uidhash_table + n);
501
502    /* Insert the root user immediately (init already runs as root) */
503    spin_lock_irq(&uidhash_lock);
504    uid_hash_insert(&root_user, uidhashentry(&init_user_ns, 0));
505    spin_unlock_irq(&uidhash_lock);
506
507    return 0;
508}
509
510module_init(uid_cache_init);
511

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