Skip to content
This repository
tree: 93d89e2d51
Fetching contributors…

Cannot retrieve contributors at this time

file 604 lines (518 sloc) 15.682 kb
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171 172 173 174 175 176 177 178 179 180 181 182 183 184 185 186 187 188 189 190 191 192 193 194 195 196 197 198 199 200 201 202 203 204 205 206 207 208 209 210 211 212 213 214 215 216 217 218 219 220 221 222 223 224 225 226 227 228 229 230 231 232 233 234 235 236 237 238 239 240 241 242 243 244 245 246 247 248 249 250 251 252 253 254 255 256 257 258 259 260 261 262 263 264 265 266 267 268 269 270 271 272 273 274 275 276 277 278 279 280 281 282 283 284 285 286 287 288 289 290 291 292 293 294 295 296 297 298 299 300 301 302 303 304 305 306 307 308 309 310 311 312 313 314 315 316 317 318 319 320 321 322 323 324 325 326 327 328 329 330 331 332 333 334 335 336 337 338 339 340 341 342 343 344 345 346 347 348 349 350 351 352 353 354 355 356 357 358 359 360 361 362 363 364 365 366 367 368 369 370 371 372 373 374 375 376 377 378 379 380 381 382 383 384 385 386 387 388 389 390 391 392 393 394 395 396 397 398 399 400 401 402 403 404 405 406 407 408 409 410 411 412 413 414 415 416 417 418 419 420 421 422 423 424 425 426 427 428 429 430 431 432 433 434 435 436 437 438 439 440 441 442 443 444 445 446 447 448 449 450 451 452 453 454 455 456 457 458 459 460 461 462 463 464 465 466 467 468 469 470 471 472 473 474 475 476 477 478 479 480 481 482 483 484 485 486 487 488 489 490 491 492 493 494 495 496 497 498 499 500 501 502 503 504 505 506 507 508 509 510 511 512 513 514 515 516 517 518 519 520 521 522 523 524 525 526 527 528 529 530 531 532 533 534 535 536 537 538 539 540 541 542 543 544 545 546 547 548 549 550 551 552 553 554 555 556 557 558 559 560 561 562 563 564 565 566 567 568 569 570 571 572 573 574 575 576 577 578 579 580 581 582 583 584 585 586 587 588 589 590 591 592 593 594 595 596 597 598 599 600 601 602 603 604
/*
* This program is free software; you can redistribute it and/or
* modify it under the terms of the GNU General Public License as
* published by the Free Software Foundation, version 2 of the
* License.
*/

#include <linux/export.h>
#include <linux/nsproxy.h>
#include <linux/slab.h>
#include <linux/user_namespace.h>
#include <linux/highuid.h>
#include <linux/cred.h>
#include <linux/securebits.h>
#include <linux/keyctl.h>
#include <linux/key-type.h>
#include <keys/user-type.h>
#include <linux/seq_file.h>
#include <linux/fs.h>
#include <linux/uaccess.h>
#include <linux/ctype.h>

static struct kmem_cache *user_ns_cachep __read_mostly;

static bool new_idmap_permitted(struct user_namespace *ns, int cap_setid,
struct uid_gid_map *map);

/*
* Create a new user namespace, deriving the creator from the user in the
* passed credentials, and replacing that user with the new root user for the
* new namespace.
*
* This is called by copy_creds(), which will finish setting the target task's
* credentials.
*/
int create_user_ns(struct cred *new)
{
struct user_namespace *ns, *parent_ns = new->user_ns;
kuid_t owner = new->euid;
kgid_t group = new->egid;

/* The creator needs a mapping in the parent user namespace
* or else we won't be able to reasonably tell userspace who
* created a user_namespace.
*/
if (!kuid_has_mapping(parent_ns, owner) ||
!kgid_has_mapping(parent_ns, group))
return -EPERM;

ns = kmem_cache_zalloc(user_ns_cachep, GFP_KERNEL);
if (!ns)
return -ENOMEM;

kref_init(&ns->kref);
ns->parent = parent_ns;
ns->owner = owner;
ns->group = group;

/* Start with the same capabilities as init but useless for doing
* anything as the capabilities are bound to the new user namespace.
*/
new->securebits = SECUREBITS_DEFAULT;
new->cap_inheritable = CAP_EMPTY_SET;
new->cap_permitted = CAP_FULL_SET;
new->cap_effective = CAP_FULL_SET;
new->cap_bset = CAP_FULL_SET;
#ifdef CONFIG_KEYS
key_put(new->request_key_auth);
new->request_key_auth = NULL;
#endif
/* tgcred will be cleared in our caller bc CLONE_THREAD won't be set */

/* Leave the new->user_ns reference with the new user namespace. */
/* Leave the reference to our user_ns with the new cred. */
new->user_ns = ns;

return 0;
}

void free_user_ns(struct kref *kref)
{
struct user_namespace *parent, *ns =
container_of(kref, struct user_namespace, kref);

parent = ns->parent;
kmem_cache_free(user_ns_cachep, ns);
put_user_ns(parent);
}
EXPORT_SYMBOL(free_user_ns);

static u32 map_id_range_down(struct uid_gid_map *map, u32 id, u32 count)
{
unsigned idx, extents;
u32 first, last, id2;

id2 = id + count - 1;

/* Find the matching extent */
extents = map->nr_extents;
smp_read_barrier_depends();
for (idx = 0; idx < extents; idx++) {
first = map->extent[idx].first;
last = first + map->extent[idx].count - 1;
if (id >= first && id <= last &&
(id2 >= first && id2 <= last))
break;
}
/* Map the id or note failure */
if (idx < extents)
id = (id - first) + map->extent[idx].lower_first;
else
id = (u32) -1;

return id;
}

static u32 map_id_down(struct uid_gid_map *map, u32 id)
{
unsigned idx, extents;
u32 first, last;

/* Find the matching extent */
extents = map->nr_extents;
smp_read_barrier_depends();
for (idx = 0; idx < extents; idx++) {
first = map->extent[idx].first;
last = first + map->extent[idx].count - 1;
if (id >= first && id <= last)
break;
}
/* Map the id or note failure */
if (idx < extents)
id = (id - first) + map->extent[idx].lower_first;
else
id = (u32) -1;

return id;
}

static u32 map_id_up(struct uid_gid_map *map, u32 id)
{
unsigned idx, extents;
u32 first, last;

/* Find the matching extent */
extents = map->nr_extents;
smp_read_barrier_depends();
for (idx = 0; idx < extents; idx++) {
first = map->extent[idx].lower_first;
last = first + map->extent[idx].count - 1;
if (id >= first && id <= last)
break;
}
/* Map the id or note failure */
if (idx < extents)
id = (id - first) + map->extent[idx].first;
else
id = (u32) -1;

return id;
}

/**
* make_kuid - Map a user-namespace uid pair into a kuid.
* @ns: User namespace that the uid is in
* @uid: User identifier
*
* Maps a user-namespace uid pair into a kernel internal kuid,
* and returns that kuid.
*
* When there is no mapping defined for the user-namespace uid
* pair INVALID_UID is returned. Callers are expected to test
* for and handle handle INVALID_UID being returned. INVALID_UID
* may be tested for using uid_valid().
*/
kuid_t make_kuid(struct user_namespace *ns, uid_t uid)
{
/* Map the uid to a global kernel uid */
return KUIDT_INIT(map_id_down(&ns->uid_map, uid));
}
EXPORT_SYMBOL(make_kuid);

/**
* from_kuid - Create a uid from a kuid user-namespace pair.
* @targ: The user namespace we want a uid in.
* @kuid: The kernel internal uid to start with.
*
* Map @kuid into the user-namespace specified by @targ and
* return the resulting uid.
*
* There is always a mapping into the initial user_namespace.
*
* If @kuid has no mapping in @targ (uid_t)-1 is returned.
*/
uid_t from_kuid(struct user_namespace *targ, kuid_t kuid)
{
/* Map the uid from a global kernel uid */
return map_id_up(&targ->uid_map, __kuid_val(kuid));
}
EXPORT_SYMBOL(from_kuid);

/**
* from_kuid_munged - Create a uid from a kuid user-namespace pair.
* @targ: The user namespace we want a uid in.
* @kuid: The kernel internal uid to start with.
*
* Map @kuid into the user-namespace specified by @targ and
* return the resulting uid.
*
* There is always a mapping into the initial user_namespace.
*
* Unlike from_kuid from_kuid_munged never fails and always
* returns a valid uid. This makes from_kuid_munged appropriate
* for use in syscalls like stat and getuid where failing the
* system call and failing to provide a valid uid are not an
* options.
*
* If @kuid has no mapping in @targ overflowuid is returned.
*/
uid_t from_kuid_munged(struct user_namespace *targ, kuid_t kuid)
{
uid_t uid;
uid = from_kuid(targ, kuid);

if (uid == (uid_t) -1)
uid = overflowuid;
return uid;
}
EXPORT_SYMBOL(from_kuid_munged);

/**
* make_kgid - Map a user-namespace gid pair into a kgid.
* @ns: User namespace that the gid is in
* @uid: group identifier
*
* Maps a user-namespace gid pair into a kernel internal kgid,
* and returns that kgid.
*
* When there is no mapping defined for the user-namespace gid
* pair INVALID_GID is returned. Callers are expected to test
* for and handle INVALID_GID being returned. INVALID_GID may be
* tested for using gid_valid().
*/
kgid_t make_kgid(struct user_namespace *ns, gid_t gid)
{
/* Map the gid to a global kernel gid */
return KGIDT_INIT(map_id_down(&ns->gid_map, gid));
}
EXPORT_SYMBOL(make_kgid);

/**
* from_kgid - Create a gid from a kgid user-namespace pair.
* @targ: The user namespace we want a gid in.
* @kgid: The kernel internal gid to start with.
*
* Map @kgid into the user-namespace specified by @targ and
* return the resulting gid.
*
* There is always a mapping into the initial user_namespace.
*
* If @kgid has no mapping in @targ (gid_t)-1 is returned.
*/
gid_t from_kgid(struct user_namespace *targ, kgid_t kgid)
{
/* Map the gid from a global kernel gid */
return map_id_up(&targ->gid_map, __kgid_val(kgid));
}
EXPORT_SYMBOL(from_kgid);

/**
* from_kgid_munged - Create a gid from a kgid user-namespace pair.
* @targ: The user namespace we want a gid in.
* @kgid: The kernel internal gid to start with.
*
* Map @kgid into the user-namespace specified by @targ and
* return the resulting gid.
*
* There is always a mapping into the initial user_namespace.
*
* Unlike from_kgid from_kgid_munged never fails and always
* returns a valid gid. This makes from_kgid_munged appropriate
* for use in syscalls like stat and getgid where failing the
* system call and failing to provide a valid gid are not options.
*
* If @kgid has no mapping in @targ overflowgid is returned.
*/
gid_t from_kgid_munged(struct user_namespace *targ, kgid_t kgid)
{
gid_t gid;
gid = from_kgid(targ, kgid);

if (gid == (gid_t) -1)
gid = overflowgid;
return gid;
}
EXPORT_SYMBOL(from_kgid_munged);

static int uid_m_show(struct seq_file *seq, void *v)
{
struct user_namespace *ns = seq->private;
struct uid_gid_extent *extent = v;
struct user_namespace *lower_ns;
uid_t lower;

lower_ns = current_user_ns();
if ((lower_ns == ns) && lower_ns->parent)
lower_ns = lower_ns->parent;

lower = from_kuid(lower_ns, KUIDT_INIT(extent->lower_first));

seq_printf(seq, "%10u %10u %10u\n",
extent->first,
lower,
extent->count);

return 0;
}

static int gid_m_show(struct seq_file *seq, void *v)
{
struct user_namespace *ns = seq->private;
struct uid_gid_extent *extent = v;
struct user_namespace *lower_ns;
gid_t lower;

lower_ns = current_user_ns();
if ((lower_ns == ns) && lower_ns->parent)
lower_ns = lower_ns->parent;

lower = from_kgid(lower_ns, KGIDT_INIT(extent->lower_first));

seq_printf(seq, "%10u %10u %10u\n",
extent->first,
lower,
extent->count);

return 0;
}

static void *m_start(struct seq_file *seq, loff_t *ppos, struct uid_gid_map *map)
{
struct uid_gid_extent *extent = NULL;
loff_t pos = *ppos;

if (pos < map->nr_extents)
extent = &map->extent[pos];

return extent;
}

static void *uid_m_start(struct seq_file *seq, loff_t *ppos)
{
struct user_namespace *ns = seq->private;

return m_start(seq, ppos, &ns->uid_map);
}

static void *gid_m_start(struct seq_file *seq, loff_t *ppos)
{
struct user_namespace *ns = seq->private;

return m_start(seq, ppos, &ns->gid_map);
}

static void *m_next(struct seq_file *seq, void *v, loff_t *pos)
{
(*pos)++;
return seq->op->start(seq, pos);
}

static void m_stop(struct seq_file *seq, void *v)
{
return;
}

struct seq_operations proc_uid_seq_operations = {
.start = uid_m_start,
.stop = m_stop,
.next = m_next,
.show = uid_m_show,
};

struct seq_operations proc_gid_seq_operations = {
.start = gid_m_start,
.stop = m_stop,
.next = m_next,
.show = gid_m_show,
};

static DEFINE_MUTEX(id_map_mutex);

static ssize_t map_write(struct file *file, const char __user *buf,
size_t count, loff_t *ppos,
int cap_setid,
struct uid_gid_map *map,
struct uid_gid_map *parent_map)
{
struct seq_file *seq = file->private_data;
struct user_namespace *ns = seq->private;
struct uid_gid_map new_map;
unsigned idx;
struct uid_gid_extent *extent, *last = NULL;
unsigned long page = 0;
char *kbuf, *pos, *next_line;
ssize_t ret = -EINVAL;

/*
* The id_map_mutex serializes all writes to any given map.
*
* Any map is only ever written once.
*
* An id map fits within 1 cache line on most architectures.
*
* On read nothing needs to be done unless you are on an
* architecture with a crazy cache coherency model like alpha.
*
* There is a one time data dependency between reading the
* count of the extents and the values of the extents. The
* desired behavior is to see the values of the extents that
* were written before the count of the extents.
*
* To achieve this smp_wmb() is used on guarantee the write
* order and smp_read_barrier_depends() is guaranteed that we
* don't have crazy architectures returning stale data.
*
*/
mutex_lock(&id_map_mutex);

ret = -EPERM;
/* Only allow one successful write to the map */
if (map->nr_extents != 0)
goto out;

/* Require the appropriate privilege CAP_SETUID or CAP_SETGID
* over the user namespace in order to set the id mapping.
*/
if (!ns_capable(ns, cap_setid))
goto out;

/* Get a buffer */
ret = -ENOMEM;
page = __get_free_page(GFP_TEMPORARY);
kbuf = (char *) page;
if (!page)
goto out;

/* Only allow <= page size writes at the beginning of the file */
ret = -EINVAL;
if ((*ppos != 0) || (count >= PAGE_SIZE))
goto out;

/* Slurp in the user data */
ret = -EFAULT;
if (copy_from_user(kbuf, buf, count))
goto out;
kbuf[count] = '\0';

/* Parse the user data */
ret = -EINVAL;
pos = kbuf;
new_map.nr_extents = 0;
for (;pos; pos = next_line) {
extent = &new_map.extent[new_map.nr_extents];

/* Find the end of line and ensure I don't look past it */
next_line = strchr(pos, '\n');
if (next_line) {
*next_line = '\0';
next_line++;
if (*next_line == '\0')
next_line = NULL;
}

pos = skip_spaces(pos);
extent->first = simple_strtoul(pos, &pos, 10);
if (!isspace(*pos))
goto out;

pos = skip_spaces(pos);
extent->lower_first = simple_strtoul(pos, &pos, 10);
if (!isspace(*pos))
goto out;

pos = skip_spaces(pos);
extent->count = simple_strtoul(pos, &pos, 10);
if (*pos && !isspace(*pos))
goto out;

/* Verify there is not trailing junk on the line */
pos = skip_spaces(pos);
if (*pos != '\0')
goto out;

/* Verify we have been given valid starting values */
if ((extent->first == (u32) -1) ||
(extent->lower_first == (u32) -1 ))
goto out;

/* Verify count is not zero and does not cause the extent to wrap */
if ((extent->first + extent->count) <= extent->first)
goto out;
if ((extent->lower_first + extent->count) <= extent->lower_first)
goto out;

/* For now only accept extents that are strictly in order */
if (last &&
(((last->first + last->count) > extent->first) ||
((last->lower_first + last->count) > extent->lower_first)))
goto out;

new_map.nr_extents++;
last = extent;

/* Fail if the file contains too many extents */
if ((new_map.nr_extents == UID_GID_MAP_MAX_EXTENTS) &&
(next_line != NULL))
goto out;
}
/* Be very certaint the new map actually exists */
if (new_map.nr_extents == 0)
goto out;

ret = -EPERM;
/* Validate the user is allowed to use user id's mapped to. */
if (!new_idmap_permitted(ns, cap_setid, &new_map))
goto out;

/* Map the lower ids from the parent user namespace to the
* kernel global id space.
*/
for (idx = 0; idx < new_map.nr_extents; idx++) {
u32 lower_first;
extent = &new_map.extent[idx];

lower_first = map_id_range_down(parent_map,
extent->lower_first,
extent->count);

/* Fail if we can not map the specified extent to
* the kernel global id space.
*/
if (lower_first == (u32) -1)
goto out;

extent->lower_first = lower_first;
}

/* Install the map */
memcpy(map->extent, new_map.extent,
new_map.nr_extents*sizeof(new_map.extent[0]));
smp_wmb();
map->nr_extents = new_map.nr_extents;

*ppos = count;
ret = count;
out:
mutex_unlock(&id_map_mutex);
if (page)
free_page(page);
return ret;
}

ssize_t proc_uid_map_write(struct file *file, const char __user *buf, size_t size, loff_t *ppos)
{
struct seq_file *seq = file->private_data;
struct user_namespace *ns = seq->private;

if (!ns->parent)
return -EPERM;

return map_write(file, buf, size, ppos, CAP_SETUID,
&ns->uid_map, &ns->parent->uid_map);
}

ssize_t proc_gid_map_write(struct file *file, const char __user *buf, size_t size, loff_t *ppos)
{
struct seq_file *seq = file->private_data;
struct user_namespace *ns = seq->private;

if (!ns->parent)
return -EPERM;

return map_write(file, buf, size, ppos, CAP_SETGID,
&ns->gid_map, &ns->parent->gid_map);
}

static bool new_idmap_permitted(struct user_namespace *ns, int cap_setid,
struct uid_gid_map *new_map)
{
/* Allow the specified ids if we have the appropriate capability
* (CAP_SETUID or CAP_SETGID) over the parent user namespace.
*/
if (ns_capable(ns->parent, cap_setid))
return true;

return false;
}

static __init int user_namespaces_init(void)
{
user_ns_cachep = KMEM_CACHE(user_namespace, SLAB_PANIC);
return 0;
}
module_init(user_namespaces_init);
Something went wrong with that request. Please try again.