Root/kernel/user_namespace.c

1/*
2 * This program is free software; you can redistribute it and/or
3 * modify it under the terms of the GNU General Public License as
4 * published by the Free Software Foundation, version 2 of the
5 * License.
6 */
7
8#include <linux/export.h>
9#include <linux/nsproxy.h>
10#include <linux/slab.h>
11#include <linux/user_namespace.h>
12#include <linux/highuid.h>
13#include <linux/cred.h>
14#include <linux/securebits.h>
15#include <linux/keyctl.h>
16#include <linux/key-type.h>
17#include <keys/user-type.h>
18#include <linux/seq_file.h>
19#include <linux/fs.h>
20#include <linux/uaccess.h>
21#include <linux/ctype.h>
22
23static struct kmem_cache *user_ns_cachep __read_mostly;
24
25static bool new_idmap_permitted(struct user_namespace *ns, int cap_setid,
26                struct uid_gid_map *map);
27
28/*
29 * Create a new user namespace, deriving the creator from the user in the
30 * passed credentials, and replacing that user with the new root user for the
31 * new namespace.
32 *
33 * This is called by copy_creds(), which will finish setting the target task's
34 * credentials.
35 */
36int create_user_ns(struct cred *new)
37{
38    struct user_namespace *ns, *parent_ns = new->user_ns;
39    kuid_t owner = new->euid;
40    kgid_t group = new->egid;
41
42    /* The creator needs a mapping in the parent user namespace
43     * or else we won't be able to reasonably tell userspace who
44     * created a user_namespace.
45     */
46    if (!kuid_has_mapping(parent_ns, owner) ||
47        !kgid_has_mapping(parent_ns, group))
48        return -EPERM;
49
50    ns = kmem_cache_zalloc(user_ns_cachep, GFP_KERNEL);
51    if (!ns)
52        return -ENOMEM;
53
54    kref_init(&ns->kref);
55    ns->parent = parent_ns;
56    ns->owner = owner;
57    ns->group = group;
58
59    /* Start with the same capabilities as init but useless for doing
60     * anything as the capabilities are bound to the new user namespace.
61     */
62    new->securebits = SECUREBITS_DEFAULT;
63    new->cap_inheritable = CAP_EMPTY_SET;
64    new->cap_permitted = CAP_FULL_SET;
65    new->cap_effective = CAP_FULL_SET;
66    new->cap_bset = CAP_FULL_SET;
67#ifdef CONFIG_KEYS
68    key_put(new->request_key_auth);
69    new->request_key_auth = NULL;
70#endif
71    /* tgcred will be cleared in our caller bc CLONE_THREAD won't be set */
72
73    /* Leave the new->user_ns reference with the new user namespace. */
74    /* Leave the reference to our user_ns with the new cred. */
75    new->user_ns = ns;
76
77    return 0;
78}
79
80void free_user_ns(struct kref *kref)
81{
82    struct user_namespace *parent, *ns =
83        container_of(kref, struct user_namespace, kref);
84
85    parent = ns->parent;
86    kmem_cache_free(user_ns_cachep, ns);
87    put_user_ns(parent);
88}
89EXPORT_SYMBOL(free_user_ns);
90
91static u32 map_id_range_down(struct uid_gid_map *map, u32 id, u32 count)
92{
93    unsigned idx, extents;
94    u32 first, last, id2;
95
96    id2 = id + count - 1;
97
98    /* Find the matching extent */
99    extents = map->nr_extents;
100    smp_read_barrier_depends();
101    for (idx = 0; idx < extents; idx++) {
102        first = map->extent[idx].first;
103        last = first + map->extent[idx].count - 1;
104        if (id >= first && id <= last &&
105            (id2 >= first && id2 <= last))
106            break;
107    }
108    /* Map the id or note failure */
109    if (idx < extents)
110        id = (id - first) + map->extent[idx].lower_first;
111    else
112        id = (u32) -1;
113
114    return id;
115}
116
117static u32 map_id_down(struct uid_gid_map *map, u32 id)
118{
119    unsigned idx, extents;
120    u32 first, last;
121
122    /* Find the matching extent */
123    extents = map->nr_extents;
124    smp_read_barrier_depends();
125    for (idx = 0; idx < extents; idx++) {
126        first = map->extent[idx].first;
127        last = first + map->extent[idx].count - 1;
128        if (id >= first && id <= last)
129            break;
130    }
131    /* Map the id or note failure */
132    if (idx < extents)
133        id = (id - first) + map->extent[idx].lower_first;
134    else
135        id = (u32) -1;
136
137    return id;
138}
139
140static u32 map_id_up(struct uid_gid_map *map, u32 id)
141{
142    unsigned idx, extents;
143    u32 first, last;
144
145    /* Find the matching extent */
146    extents = map->nr_extents;
147    smp_read_barrier_depends();
148    for (idx = 0; idx < extents; idx++) {
149        first = map->extent[idx].lower_first;
150        last = first + map->extent[idx].count - 1;
151        if (id >= first && id <= last)
152            break;
153    }
154    /* Map the id or note failure */
155    if (idx < extents)
156        id = (id - first) + map->extent[idx].first;
157    else
158        id = (u32) -1;
159
160    return id;
161}
162
163/**
164 * make_kuid - Map a user-namespace uid pair into a kuid.
165 * @ns: User namespace that the uid is in
166 * @uid: User identifier
167 *
168 * Maps a user-namespace uid pair into a kernel internal kuid,
169 * and returns that kuid.
170 *
171 * When there is no mapping defined for the user-namespace uid
172 * pair INVALID_UID is returned. Callers are expected to test
173 * for and handle handle INVALID_UID being returned. INVALID_UID
174 * may be tested for using uid_valid().
175 */
176kuid_t make_kuid(struct user_namespace *ns, uid_t uid)
177{
178    /* Map the uid to a global kernel uid */
179    return KUIDT_INIT(map_id_down(&ns->uid_map, uid));
180}
181EXPORT_SYMBOL(make_kuid);
182
183/**
184 * from_kuid - Create a uid from a kuid user-namespace pair.
185 * @targ: The user namespace we want a uid in.
186 * @kuid: The kernel internal uid to start with.
187 *
188 * Map @kuid into the user-namespace specified by @targ and
189 * return the resulting uid.
190 *
191 * There is always a mapping into the initial user_namespace.
192 *
193 * If @kuid has no mapping in @targ (uid_t)-1 is returned.
194 */
195uid_t from_kuid(struct user_namespace *targ, kuid_t kuid)
196{
197    /* Map the uid from a global kernel uid */
198    return map_id_up(&targ->uid_map, __kuid_val(kuid));
199}
200EXPORT_SYMBOL(from_kuid);
201
202/**
203 * from_kuid_munged - Create a uid from a kuid user-namespace pair.
204 * @targ: The user namespace we want a uid in.
205 * @kuid: The kernel internal uid to start with.
206 *
207 * Map @kuid into the user-namespace specified by @targ and
208 * return the resulting uid.
209 *
210 * There is always a mapping into the initial user_namespace.
211 *
212 * Unlike from_kuid from_kuid_munged never fails and always
213 * returns a valid uid. This makes from_kuid_munged appropriate
214 * for use in syscalls like stat and getuid where failing the
215 * system call and failing to provide a valid uid are not an
216 * options.
217 *
218 * If @kuid has no mapping in @targ overflowuid is returned.
219 */
220uid_t from_kuid_munged(struct user_namespace *targ, kuid_t kuid)
221{
222    uid_t uid;
223    uid = from_kuid(targ, kuid);
224
225    if (uid == (uid_t) -1)
226        uid = overflowuid;
227    return uid;
228}
229EXPORT_SYMBOL(from_kuid_munged);
230
231/**
232 * make_kgid - Map a user-namespace gid pair into a kgid.
233 * @ns: User namespace that the gid is in
234 * @uid: group identifier
235 *
236 * Maps a user-namespace gid pair into a kernel internal kgid,
237 * and returns that kgid.
238 *
239 * When there is no mapping defined for the user-namespace gid
240 * pair INVALID_GID is returned. Callers are expected to test
241 * for and handle INVALID_GID being returned. INVALID_GID may be
242 * tested for using gid_valid().
243 */
244kgid_t make_kgid(struct user_namespace *ns, gid_t gid)
245{
246    /* Map the gid to a global kernel gid */
247    return KGIDT_INIT(map_id_down(&ns->gid_map, gid));
248}
249EXPORT_SYMBOL(make_kgid);
250
251/**
252 * from_kgid - Create a gid from a kgid user-namespace pair.
253 * @targ: The user namespace we want a gid in.
254 * @kgid: The kernel internal gid to start with.
255 *
256 * Map @kgid into the user-namespace specified by @targ and
257 * return the resulting gid.
258 *
259 * There is always a mapping into the initial user_namespace.
260 *
261 * If @kgid has no mapping in @targ (gid_t)-1 is returned.
262 */
263gid_t from_kgid(struct user_namespace *targ, kgid_t kgid)
264{
265    /* Map the gid from a global kernel gid */
266    return map_id_up(&targ->gid_map, __kgid_val(kgid));
267}
268EXPORT_SYMBOL(from_kgid);
269
270/**
271 * from_kgid_munged - Create a gid from a kgid user-namespace pair.
272 * @targ: The user namespace we want a gid in.
273 * @kgid: The kernel internal gid to start with.
274 *
275 * Map @kgid into the user-namespace specified by @targ and
276 * return the resulting gid.
277 *
278 * There is always a mapping into the initial user_namespace.
279 *
280 * Unlike from_kgid from_kgid_munged never fails and always
281 * returns a valid gid. This makes from_kgid_munged appropriate
282 * for use in syscalls like stat and getgid where failing the
283 * system call and failing to provide a valid gid are not options.
284 *
285 * If @kgid has no mapping in @targ overflowgid is returned.
286 */
287gid_t from_kgid_munged(struct user_namespace *targ, kgid_t kgid)
288{
289    gid_t gid;
290    gid = from_kgid(targ, kgid);
291
292    if (gid == (gid_t) -1)
293        gid = overflowgid;
294    return gid;
295}
296EXPORT_SYMBOL(from_kgid_munged);
297
298static int uid_m_show(struct seq_file *seq, void *v)
299{
300    struct user_namespace *ns = seq->private;
301    struct uid_gid_extent *extent = v;
302    struct user_namespace *lower_ns;
303    uid_t lower;
304
305    lower_ns = current_user_ns();
306    if ((lower_ns == ns) && lower_ns->parent)
307        lower_ns = lower_ns->parent;
308
309    lower = from_kuid(lower_ns, KUIDT_INIT(extent->lower_first));
310
311    seq_printf(seq, "%10u %10u %10u\n",
312        extent->first,
313        lower,
314        extent->count);
315
316    return 0;
317}
318
319static int gid_m_show(struct seq_file *seq, void *v)
320{
321    struct user_namespace *ns = seq->private;
322    struct uid_gid_extent *extent = v;
323    struct user_namespace *lower_ns;
324    gid_t lower;
325
326    lower_ns = current_user_ns();
327    if ((lower_ns == ns) && lower_ns->parent)
328        lower_ns = lower_ns->parent;
329
330    lower = from_kgid(lower_ns, KGIDT_INIT(extent->lower_first));
331
332    seq_printf(seq, "%10u %10u %10u\n",
333        extent->first,
334        lower,
335        extent->count);
336
337    return 0;
338}
339
340static void *m_start(struct seq_file *seq, loff_t *ppos, struct uid_gid_map *map)
341{
342    struct uid_gid_extent *extent = NULL;
343    loff_t pos = *ppos;
344
345    if (pos < map->nr_extents)
346        extent = &map->extent[pos];
347
348    return extent;
349}
350
351static void *uid_m_start(struct seq_file *seq, loff_t *ppos)
352{
353    struct user_namespace *ns = seq->private;
354
355    return m_start(seq, ppos, &ns->uid_map);
356}
357
358static void *gid_m_start(struct seq_file *seq, loff_t *ppos)
359{
360    struct user_namespace *ns = seq->private;
361
362    return m_start(seq, ppos, &ns->gid_map);
363}
364
365static void *m_next(struct seq_file *seq, void *v, loff_t *pos)
366{
367    (*pos)++;
368    return seq->op->start(seq, pos);
369}
370
371static void m_stop(struct seq_file *seq, void *v)
372{
373    return;
374}
375
376struct seq_operations proc_uid_seq_operations = {
377    .start = uid_m_start,
378    .stop = m_stop,
379    .next = m_next,
380    .show = uid_m_show,
381};
382
383struct seq_operations proc_gid_seq_operations = {
384    .start = gid_m_start,
385    .stop = m_stop,
386    .next = m_next,
387    .show = gid_m_show,
388};
389
390static DEFINE_MUTEX(id_map_mutex);
391
392static ssize_t map_write(struct file *file, const char __user *buf,
393             size_t count, loff_t *ppos,
394             int cap_setid,
395             struct uid_gid_map *map,
396             struct uid_gid_map *parent_map)
397{
398    struct seq_file *seq = file->private_data;
399    struct user_namespace *ns = seq->private;
400    struct uid_gid_map new_map;
401    unsigned idx;
402    struct uid_gid_extent *extent, *last = NULL;
403    unsigned long page = 0;
404    char *kbuf, *pos, *next_line;
405    ssize_t ret = -EINVAL;
406
407    /*
408     * The id_map_mutex serializes all writes to any given map.
409     *
410     * Any map is only ever written once.
411     *
412     * An id map fits within 1 cache line on most architectures.
413     *
414     * On read nothing needs to be done unless you are on an
415     * architecture with a crazy cache coherency model like alpha.
416     *
417     * There is a one time data dependency between reading the
418     * count of the extents and the values of the extents. The
419     * desired behavior is to see the values of the extents that
420     * were written before the count of the extents.
421     *
422     * To achieve this smp_wmb() is used on guarantee the write
423     * order and smp_read_barrier_depends() is guaranteed that we
424     * don't have crazy architectures returning stale data.
425     *
426     */
427    mutex_lock(&id_map_mutex);
428
429    ret = -EPERM;
430    /* Only allow one successful write to the map */
431    if (map->nr_extents != 0)
432        goto out;
433
434    /* Require the appropriate privilege CAP_SETUID or CAP_SETGID
435     * over the user namespace in order to set the id mapping.
436     */
437    if (!ns_capable(ns, cap_setid))
438        goto out;
439
440    /* Get a buffer */
441    ret = -ENOMEM;
442    page = __get_free_page(GFP_TEMPORARY);
443    kbuf = (char *) page;
444    if (!page)
445        goto out;
446
447    /* Only allow <= page size writes at the beginning of the file */
448    ret = -EINVAL;
449    if ((*ppos != 0) || (count >= PAGE_SIZE))
450        goto out;
451
452    /* Slurp in the user data */
453    ret = -EFAULT;
454    if (copy_from_user(kbuf, buf, count))
455        goto out;
456    kbuf[count] = '\0';
457
458    /* Parse the user data */
459    ret = -EINVAL;
460    pos = kbuf;
461    new_map.nr_extents = 0;
462    for (;pos; pos = next_line) {
463        extent = &new_map.extent[new_map.nr_extents];
464
465        /* Find the end of line and ensure I don't look past it */
466        next_line = strchr(pos, '\n');
467        if (next_line) {
468            *next_line = '\0';
469            next_line++;
470            if (*next_line == '\0')
471                next_line = NULL;
472        }
473
474        pos = skip_spaces(pos);
475        extent->first = simple_strtoul(pos, &pos, 10);
476        if (!isspace(*pos))
477            goto out;
478
479        pos = skip_spaces(pos);
480        extent->lower_first = simple_strtoul(pos, &pos, 10);
481        if (!isspace(*pos))
482            goto out;
483
484        pos = skip_spaces(pos);
485        extent->count = simple_strtoul(pos, &pos, 10);
486        if (*pos && !isspace(*pos))
487            goto out;
488
489        /* Verify there is not trailing junk on the line */
490        pos = skip_spaces(pos);
491        if (*pos != '\0')
492            goto out;
493
494        /* Verify we have been given valid starting values */
495        if ((extent->first == (u32) -1) ||
496            (extent->lower_first == (u32) -1 ))
497            goto out;
498
499        /* Verify count is not zero and does not cause the extent to wrap */
500        if ((extent->first + extent->count) <= extent->first)
501            goto out;
502        if ((extent->lower_first + extent->count) <= extent->lower_first)
503            goto out;
504
505        /* For now only accept extents that are strictly in order */
506        if (last &&
507            (((last->first + last->count) > extent->first) ||
508             ((last->lower_first + last->count) > extent->lower_first)))
509            goto out;
510
511        new_map.nr_extents++;
512        last = extent;
513
514        /* Fail if the file contains too many extents */
515        if ((new_map.nr_extents == UID_GID_MAP_MAX_EXTENTS) &&
516            (next_line != NULL))
517            goto out;
518    }
519    /* Be very certaint the new map actually exists */
520    if (new_map.nr_extents == 0)
521        goto out;
522
523    ret = -EPERM;
524    /* Validate the user is allowed to use user id's mapped to. */
525    if (!new_idmap_permitted(ns, cap_setid, &new_map))
526        goto out;
527
528    /* Map the lower ids from the parent user namespace to the
529     * kernel global id space.
530     */
531    for (idx = 0; idx < new_map.nr_extents; idx++) {
532        u32 lower_first;
533        extent = &new_map.extent[idx];
534
535        lower_first = map_id_range_down(parent_map,
536                        extent->lower_first,
537                        extent->count);
538
539        /* Fail if we can not map the specified extent to
540         * the kernel global id space.
541         */
542        if (lower_first == (u32) -1)
543            goto out;
544
545        extent->lower_first = lower_first;
546    }
547
548    /* Install the map */
549    memcpy(map->extent, new_map.extent,
550        new_map.nr_extents*sizeof(new_map.extent[0]));
551    smp_wmb();
552    map->nr_extents = new_map.nr_extents;
553
554    *ppos = count;
555    ret = count;
556out:
557    mutex_unlock(&id_map_mutex);
558    if (page)
559        free_page(page);
560    return ret;
561}
562
563ssize_t proc_uid_map_write(struct file *file, const char __user *buf, size_t size, loff_t *ppos)
564{
565    struct seq_file *seq = file->private_data;
566    struct user_namespace *ns = seq->private;
567
568    if (!ns->parent)
569        return -EPERM;
570
571    return map_write(file, buf, size, ppos, CAP_SETUID,
572             &ns->uid_map, &ns->parent->uid_map);
573}
574
575ssize_t proc_gid_map_write(struct file *file, const char __user *buf, size_t size, loff_t *ppos)
576{
577    struct seq_file *seq = file->private_data;
578    struct user_namespace *ns = seq->private;
579
580    if (!ns->parent)
581        return -EPERM;
582
583    return map_write(file, buf, size, ppos, CAP_SETGID,
584             &ns->gid_map, &ns->parent->gid_map);
585}
586
587static bool new_idmap_permitted(struct user_namespace *ns, int cap_setid,
588                struct uid_gid_map *new_map)
589{
590    /* Allow the specified ids if we have the appropriate capability
591     * (CAP_SETUID or CAP_SETGID) over the parent user namespace.
592     */
593    if (ns_capable(ns->parent, cap_setid))
594        return true;
595
596    return false;
597}
598
599static __init int user_namespaces_init(void)
600{
601    user_ns_cachep = KMEM_CACHE(user_namespace, SLAB_PANIC);
602    return 0;
603}
604module_init(user_namespaces_init);
605

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