1 /*-
2 * Copyright (c) 2008-2011 Robert N. M. Watson
3 * Copyright (c) 2010-2011 Jonathan Anderson
4 * Copyright (c) 2012 FreeBSD Foundation
5 * All rights reserved.
6 *
7 * This software was developed at the University of Cambridge Computer
8 * Laboratory with support from a grant from Google, Inc.
9 *
10 * Portions of this software were developed by Pawel Jakub Dawidek under
11 * sponsorship from the FreeBSD Foundation.
12 *
13 * Redistribution and use in source and binary forms, with or without
14 * modification, are permitted provided that the following conditions
15 * are met:
16 * 1. Redistributions of source code must retain the above copyright
17 * notice, this list of conditions and the following disclaimer.
18 * 2. Redistributions in binary form must reproduce the above copyright
19 * notice, this list of conditions and the following disclaimer in the
20 * documentation and/or other materials provided with the distribution.
21 *
22 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
23 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
24 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
25 * ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
26 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
27 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
28 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
29 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
30 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
31 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
32 * SUCH DAMAGE.
33 */
34
35 /*
36 * FreeBSD kernel capability facility.
37 *
38 * Two kernel features are implemented here: capability mode, a sandboxed mode
39 * of execution for processes, and capabilities, a refinement on file
40 * descriptors that allows fine-grained control over operations on the file
41 * descriptor. Collectively, these allow processes to run in the style of a
42 * historic "capability system" in which they can use only resources
43 * explicitly delegated to them. This model is enforced by restricting access
44 * to global namespaces in capability mode.
45 *
46 * Capabilities wrap other file descriptor types, binding them to a constant
47 * rights mask set when the capability is created. New capabilities may be
48 * derived from existing capabilities, but only if they have the same or a
49 * strict subset of the rights on the original capability.
50 *
51 * System calls permitted in capability mode are defined in capabilities.conf;
52 * calls must be carefully audited for safety to ensure that they don't allow
53 * escape from a sandbox. Some calls permit only a subset of operations in
54 * capability mode -- for example, shm_open(2) is limited to creating
55 * anonymous, rather than named, POSIX shared memory objects.
56 */
57
58 #include <sys/cdefs.h>
59 __FBSDID("$FreeBSD: releng/11.2/sys/kern/sys_capability.c 330355 2018-03-03 21:05:28Z eadler $");
60
61 #include "opt_capsicum.h"
62 #include "opt_ktrace.h"
63
64 #include <sys/param.h>
65 #include <sys/capsicum.h>
66 #include <sys/file.h>
67 #include <sys/filedesc.h>
68 #include <sys/kernel.h>
69 #include <sys/limits.h>
70 #include <sys/lock.h>
71 #include <sys/mutex.h>
72 #include <sys/proc.h>
73 #include <sys/syscallsubr.h>
74 #include <sys/sysproto.h>
75 #include <sys/sysctl.h>
76 #include <sys/systm.h>
77 #include <sys/ucred.h>
78 #include <sys/uio.h>
79 #include <sys/ktrace.h>
80
81 #include <security/audit/audit.h>
82
83 #include <vm/uma.h>
84 #include <vm/vm.h>
85
86 int trap_enotcap;
87 SYSCTL_INT(_kern, OID_AUTO, trap_enotcap, CTLFLAG_RW, &trap_enotcap, 0,
88 "Deliver SIGTRAP on ENOTCAPABLE");
89
90 #ifdef CAPABILITY_MODE
91
92 FEATURE(security_capability_mode, "Capsicum Capability Mode");
93
94 /*
95 * System call to enter capability mode for the process.
96 */
97 int
98 sys_cap_enter(struct thread *td, struct cap_enter_args *uap)
99 {
100 struct ucred *newcred, *oldcred;
101 struct proc *p;
102
103 if (IN_CAPABILITY_MODE(td))
104 return (0);
105
106 newcred = crget();
107 p = td->td_proc;
108 PROC_LOCK(p);
109 oldcred = crcopysafe(p, newcred);
110 newcred->cr_flags |= CRED_FLAG_CAPMODE;
111 proc_set_cred(p, newcred);
112 PROC_UNLOCK(p);
113 crfree(oldcred);
114 return (0);
115 }
116
117 /*
118 * System call to query whether the process is in capability mode.
119 */
120 int
121 sys_cap_getmode(struct thread *td, struct cap_getmode_args *uap)
122 {
123 u_int i;
124
125 i = IN_CAPABILITY_MODE(td) ? 1 : 0;
126 return (copyout(&i, uap->modep, sizeof(i)));
127 }
128
129 #else /* !CAPABILITY_MODE */
130
131 int
132 sys_cap_enter(struct thread *td, struct cap_enter_args *uap)
133 {
134
135 return (ENOSYS);
136 }
137
138 int
139 sys_cap_getmode(struct thread *td, struct cap_getmode_args *uap)
140 {
141
142 return (ENOSYS);
143 }
144
145 #endif /* CAPABILITY_MODE */
146
147 #ifdef CAPABILITIES
148
149 FEATURE(security_capabilities, "Capsicum Capabilities");
150
151 MALLOC_DECLARE(M_FILECAPS);
152
153 static inline int
154 _cap_check(const cap_rights_t *havep, const cap_rights_t *needp,
155 enum ktr_cap_fail_type type)
156 {
157
158 if (!cap_rights_contains(havep, needp)) {
159 #ifdef KTRACE
160 if (KTRPOINT(curthread, KTR_CAPFAIL))
161 ktrcapfail(type, needp, havep);
162 #endif
163 return (ENOTCAPABLE);
164 }
165 return (0);
166 }
167
168 /*
169 * Test whether a capability grants the requested rights.
170 */
171 int
172 cap_check(const cap_rights_t *havep, const cap_rights_t *needp)
173 {
174
175 return (_cap_check(havep, needp, CAPFAIL_NOTCAPABLE));
176 }
177
178 /*
179 * Convert capability rights into VM access flags.
180 */
181 u_char
182 cap_rights_to_vmprot(cap_rights_t *havep)
183 {
184 u_char maxprot;
185
186 maxprot = VM_PROT_NONE;
187 if (cap_rights_is_set(havep, CAP_MMAP_R))
188 maxprot |= VM_PROT_READ;
189 if (cap_rights_is_set(havep, CAP_MMAP_W))
190 maxprot |= VM_PROT_WRITE;
191 if (cap_rights_is_set(havep, CAP_MMAP_X))
192 maxprot |= VM_PROT_EXECUTE;
193
194 return (maxprot);
195 }
196
197 /*
198 * Extract rights from a capability for monitoring purposes -- not for use in
199 * any other way, as we want to keep all capability permission evaluation in
200 * this one file.
201 */
202
203 cap_rights_t *
204 cap_rights_fde(struct filedescent *fde)
205 {
206
207 return (&fde->fde_rights);
208 }
209
210 cap_rights_t *
211 cap_rights(struct filedesc *fdp, int fd)
212 {
213
214 return (cap_rights_fde(&fdp->fd_ofiles[fd]));
215 }
216
217 int
218 kern_cap_rights_limit(struct thread *td, int fd, cap_rights_t *rights)
219 {
220 struct filedesc *fdp;
221 int error;
222
223 fdp = td->td_proc->p_fd;
224 FILEDESC_XLOCK(fdp);
225 if (fget_locked(fdp, fd) == NULL) {
226 FILEDESC_XUNLOCK(fdp);
227 return (EBADF);
228 }
229 error = _cap_check(cap_rights(fdp, fd), rights, CAPFAIL_INCREASE);
230 if (error == 0) {
231 fdp->fd_ofiles[fd].fde_rights = *rights;
232 if (!cap_rights_is_set(rights, CAP_IOCTL)) {
233 free(fdp->fd_ofiles[fd].fde_ioctls, M_FILECAPS);
234 fdp->fd_ofiles[fd].fde_ioctls = NULL;
235 fdp->fd_ofiles[fd].fde_nioctls = 0;
236 }
237 if (!cap_rights_is_set(rights, CAP_FCNTL))
238 fdp->fd_ofiles[fd].fde_fcntls = 0;
239 }
240 FILEDESC_XUNLOCK(fdp);
241 return (error);
242 }
243
244 /*
245 * System call to limit rights of the given capability.
246 */
247 int
248 sys_cap_rights_limit(struct thread *td, struct cap_rights_limit_args *uap)
249 {
250 cap_rights_t rights;
251 int error, version;
252
253 cap_rights_init(&rights);
254
255 error = copyin(uap->rightsp, &rights, sizeof(rights.cr_rights[0]));
256 if (error != 0)
257 return (error);
258 version = CAPVER(&rights);
259 if (version != CAP_RIGHTS_VERSION_00)
260 return (EINVAL);
261
262 error = copyin(uap->rightsp, &rights,
263 sizeof(rights.cr_rights[0]) * CAPARSIZE(&rights));
264 if (error != 0)
265 return (error);
266 /* Check for race. */
267 if (CAPVER(&rights) != version)
268 return (EINVAL);
269
270 if (!cap_rights_is_valid(&rights))
271 return (EINVAL);
272
273 if (version != CAP_RIGHTS_VERSION) {
274 rights.cr_rights[0] &= ~(0x3ULL << 62);
275 rights.cr_rights[0] |= ((uint64_t)CAP_RIGHTS_VERSION << 62);
276 }
277 #ifdef KTRACE
278 if (KTRPOINT(td, KTR_STRUCT))
279 ktrcaprights(&rights);
280 #endif
281
282 AUDIT_ARG_FD(uap->fd);
283 AUDIT_ARG_RIGHTS(&rights);
284 return (kern_cap_rights_limit(td, uap->fd, &rights));
285 }
286
287 /*
288 * System call to query the rights mask associated with a capability.
289 */
290 int
291 sys___cap_rights_get(struct thread *td, struct __cap_rights_get_args *uap)
292 {
293 struct filedesc *fdp;
294 cap_rights_t rights;
295 int error, fd, i, n;
296
297 if (uap->version != CAP_RIGHTS_VERSION_00)
298 return (EINVAL);
299
300 fd = uap->fd;
301
302 AUDIT_ARG_FD(fd);
303
304 fdp = td->td_proc->p_fd;
305 FILEDESC_SLOCK(fdp);
306 if (fget_locked(fdp, fd) == NULL) {
307 FILEDESC_SUNLOCK(fdp);
308 return (EBADF);
309 }
310 rights = *cap_rights(fdp, fd);
311 FILEDESC_SUNLOCK(fdp);
312 n = uap->version + 2;
313 if (uap->version != CAPVER(&rights)) {
314 /*
315 * For older versions we need to check if the descriptor
316 * doesn't contain rights not understood by the caller.
317 * If it does, we have to return an error.
318 */
319 for (i = n; i < CAPARSIZE(&rights); i++) {
320 if ((rights.cr_rights[i] & ~(0x7FULL << 57)) != 0)
321 return (EINVAL);
322 }
323 }
324 error = copyout(&rights, uap->rightsp, sizeof(rights.cr_rights[0]) * n);
325 #ifdef KTRACE
326 if (error == 0 && KTRPOINT(td, KTR_STRUCT))
327 ktrcaprights(&rights);
328 #endif
329 return (error);
330 }
331
332 /*
333 * Test whether a capability grants the given ioctl command.
334 * If descriptor doesn't have CAP_IOCTL, then ioctls list is empty and
335 * ENOTCAPABLE will be returned.
336 */
337 int
338 cap_ioctl_check(struct filedesc *fdp, int fd, u_long cmd)
339 {
340 u_long *cmds;
341 ssize_t ncmds;
342 long i;
343
344 FILEDESC_LOCK_ASSERT(fdp);
345 KASSERT(fd >= 0 && fd < fdp->fd_nfiles,
346 ("%s: invalid fd=%d", __func__, fd));
347
348 ncmds = fdp->fd_ofiles[fd].fde_nioctls;
349 if (ncmds == -1)
350 return (0);
351
352 cmds = fdp->fd_ofiles[fd].fde_ioctls;
353 for (i = 0; i < ncmds; i++) {
354 if (cmds[i] == cmd)
355 return (0);
356 }
357
358 return (ENOTCAPABLE);
359 }
360
361 /*
362 * Check if the current ioctls list can be replaced by the new one.
363 */
364 static int
365 cap_ioctl_limit_check(struct filedesc *fdp, int fd, const u_long *cmds,
366 size_t ncmds)
367 {
368 u_long *ocmds;
369 ssize_t oncmds;
370 u_long i;
371 long j;
372
373 oncmds = fdp->fd_ofiles[fd].fde_nioctls;
374 if (oncmds == -1)
375 return (0);
376 if (oncmds < (ssize_t)ncmds)
377 return (ENOTCAPABLE);
378
379 ocmds = fdp->fd_ofiles[fd].fde_ioctls;
380 for (i = 0; i < ncmds; i++) {
381 for (j = 0; j < oncmds; j++) {
382 if (cmds[i] == ocmds[j])
383 break;
384 }
385 if (j == oncmds)
386 return (ENOTCAPABLE);
387 }
388
389 return (0);
390 }
391
392 int
393 kern_cap_ioctls_limit(struct thread *td, int fd, u_long *cmds, size_t ncmds)
394 {
395 struct filedesc *fdp;
396 u_long *ocmds;
397 int error;
398
399 AUDIT_ARG_FD(fd);
400
401 fdp = td->td_proc->p_fd;
402 FILEDESC_XLOCK(fdp);
403
404 if (fget_locked(fdp, fd) == NULL) {
405 error = EBADF;
406 goto out;
407 }
408
409 error = cap_ioctl_limit_check(fdp, fd, cmds, ncmds);
410 if (error != 0)
411 goto out;
412
413 ocmds = fdp->fd_ofiles[fd].fde_ioctls;
414 fdp->fd_ofiles[fd].fde_ioctls = cmds;
415 fdp->fd_ofiles[fd].fde_nioctls = ncmds;
416
417 cmds = ocmds;
418 error = 0;
419 out:
420 FILEDESC_XUNLOCK(fdp);
421 free(cmds, M_FILECAPS);
422 return (error);
423 }
424
425 int
426 sys_cap_ioctls_limit(struct thread *td, struct cap_ioctls_limit_args *uap)
427 {
428 u_long *cmds;
429 size_t ncmds;
430 int error;
431
432 ncmds = uap->ncmds;
433
434 if (ncmds > 256) /* XXX: Is 256 sane? */
435 return (EINVAL);
436
437 if (ncmds == 0) {
438 cmds = NULL;
439 } else {
440 cmds = malloc(sizeof(cmds[0]) * ncmds, M_FILECAPS, M_WAITOK);
441 error = copyin(uap->cmds, cmds, sizeof(cmds[0]) * ncmds);
442 if (error != 0) {
443 free(cmds, M_FILECAPS);
444 return (error);
445 }
446 }
447
448 return (kern_cap_ioctls_limit(td, uap->fd, cmds, ncmds));
449 }
450
451 int
452 sys_cap_ioctls_get(struct thread *td, struct cap_ioctls_get_args *uap)
453 {
454 struct filedesc *fdp;
455 struct filedescent *fdep;
456 u_long *cmds;
457 size_t maxcmds;
458 int error, fd;
459
460 fd = uap->fd;
461 cmds = uap->cmds;
462 maxcmds = uap->maxcmds;
463
464 AUDIT_ARG_FD(fd);
465
466 fdp = td->td_proc->p_fd;
467 FILEDESC_SLOCK(fdp);
468
469 if (fget_locked(fdp, fd) == NULL) {
470 error = EBADF;
471 goto out;
472 }
473
474 /*
475 * If all ioctls are allowed (fde_nioctls == -1 && fde_ioctls == NULL)
476 * the only sane thing we can do is to not populate the given array and
477 * return CAP_IOCTLS_ALL.
478 */
479
480 fdep = &fdp->fd_ofiles[fd];
481 if (cmds != NULL && fdep->fde_ioctls != NULL) {
482 error = copyout(fdep->fde_ioctls, cmds,
483 sizeof(cmds[0]) * MIN(fdep->fde_nioctls, maxcmds));
484 if (error != 0)
485 goto out;
486 }
487 if (fdep->fde_nioctls == -1)
488 td->td_retval[0] = CAP_IOCTLS_ALL;
489 else
490 td->td_retval[0] = fdep->fde_nioctls;
491
492 error = 0;
493 out:
494 FILEDESC_SUNLOCK(fdp);
495 return (error);
496 }
497
498 /*
499 * Test whether a capability grants the given fcntl command.
500 */
501 int
502 cap_fcntl_check_fde(struct filedescent *fde, int cmd)
503 {
504 uint32_t fcntlcap;
505
506 fcntlcap = (1 << cmd);
507 KASSERT((CAP_FCNTL_ALL & fcntlcap) != 0,
508 ("Unsupported fcntl=%d.", cmd));
509
510 if ((fde->fde_fcntls & fcntlcap) != 0)
511 return (0);
512
513 return (ENOTCAPABLE);
514 }
515
516 int
517 cap_fcntl_check(struct filedesc *fdp, int fd, int cmd)
518 {
519
520 KASSERT(fd >= 0 && fd < fdp->fd_nfiles,
521 ("%s: invalid fd=%d", __func__, fd));
522
523 return (cap_fcntl_check_fde(&fdp->fd_ofiles[fd], cmd));
524 }
525
526 int
527 sys_cap_fcntls_limit(struct thread *td, struct cap_fcntls_limit_args *uap)
528 {
529 struct filedesc *fdp;
530 uint32_t fcntlrights;
531 int fd;
532
533 fd = uap->fd;
534 fcntlrights = uap->fcntlrights;
535
536 AUDIT_ARG_FD(fd);
537 AUDIT_ARG_FCNTL_RIGHTS(fcntlrights);
538
539 if ((fcntlrights & ~CAP_FCNTL_ALL) != 0)
540 return (EINVAL);
541
542 fdp = td->td_proc->p_fd;
543 FILEDESC_XLOCK(fdp);
544
545 if (fget_locked(fdp, fd) == NULL) {
546 FILEDESC_XUNLOCK(fdp);
547 return (EBADF);
548 }
549
550 if ((fcntlrights & ~fdp->fd_ofiles[fd].fde_fcntls) != 0) {
551 FILEDESC_XUNLOCK(fdp);
552 return (ENOTCAPABLE);
553 }
554
555 fdp->fd_ofiles[fd].fde_fcntls = fcntlrights;
556 FILEDESC_XUNLOCK(fdp);
557
558 return (0);
559 }
560
561 int
562 sys_cap_fcntls_get(struct thread *td, struct cap_fcntls_get_args *uap)
563 {
564 struct filedesc *fdp;
565 uint32_t rights;
566 int fd;
567
568 fd = uap->fd;
569
570 AUDIT_ARG_FD(fd);
571
572 fdp = td->td_proc->p_fd;
573 FILEDESC_SLOCK(fdp);
574 if (fget_locked(fdp, fd) == NULL) {
575 FILEDESC_SUNLOCK(fdp);
576 return (EBADF);
577 }
578 rights = fdp->fd_ofiles[fd].fde_fcntls;
579 FILEDESC_SUNLOCK(fdp);
580
581 return (copyout(&rights, uap->fcntlrightsp, sizeof(rights)));
582 }
583
584 #else /* !CAPABILITIES */
585
586 /*
587 * Stub Capability functions for when options CAPABILITIES isn't compiled
588 * into the kernel.
589 */
590
591 int
592 sys_cap_rights_limit(struct thread *td, struct cap_rights_limit_args *uap)
593 {
594
595 return (ENOSYS);
596 }
597
598 int
599 sys___cap_rights_get(struct thread *td, struct __cap_rights_get_args *uap)
600 {
601
602 return (ENOSYS);
603 }
604
605 int
606 sys_cap_ioctls_limit(struct thread *td, struct cap_ioctls_limit_args *uap)
607 {
608
609 return (ENOSYS);
610 }
611
612 int
613 sys_cap_ioctls_get(struct thread *td, struct cap_ioctls_get_args *uap)
614 {
615
616 return (ENOSYS);
617 }
618
619 int
620 sys_cap_fcntls_limit(struct thread *td, struct cap_fcntls_limit_args *uap)
621 {
622
623 return (ENOSYS);
624 }
625
626 int
627 sys_cap_fcntls_get(struct thread *td, struct cap_fcntls_get_args *uap)
628 {
629
630 return (ENOSYS);
631 }
632
633 #endif /* CAPABILITIES */
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