1 /*-
2 * Copyright (c) 2008-2011 Robert N. M. Watson
3 * Copyright (c) 2010-2011 Jonathan Anderson
4 * All rights reserved.
5 *
6 * This software was developed at the University of Cambridge Computer
7 * Laboratory with support from a grant from Google, Inc.
8 *
9 * Redistribution and use in source and binary forms, with or without
10 * modification, are permitted provided that the following conditions
11 * are met:
12 * 1. Redistributions of source code must retain the above copyright
13 * notice, this list of conditions and the following disclaimer.
14 * 2. Redistributions in binary form must reproduce the above copyright
15 * notice, this list of conditions and the following disclaimer in the
16 * documentation and/or other materials provided with the distribution.
17 *
18 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
19 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
20 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
21 * ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
22 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
23 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
24 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
25 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
26 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
27 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
28 * SUCH DAMAGE.
29 */
30
31 /*
32 * FreeBSD kernel capability facility.
33 *
34 * Two kernel features are implemented here: capability mode, a sandboxed mode
35 * of execution for processes, and capabilities, a refinement on file
36 * descriptors that allows fine-grained control over operations on the file
37 * descriptor. Collectively, these allow processes to run in the style of a
38 * historic "capability system" in which they can use only resources
39 * explicitly delegated to them. This model is enforced by restricting access
40 * to global namespaces in capability mode.
41 *
42 * Capabilities wrap other file descriptor types, binding them to a constant
43 * rights mask set when the capability is created. New capabilities may be
44 * derived from existing capabilities, but only if they have the same or a
45 * strict subset of the rights on the original capability.
46 *
47 * System calls permitted in capability mode are defined in capabilities.conf;
48 * calls must be carefully audited for safety to ensure that they don't allow
49 * escape from a sandbox. Some calls permit only a subset of operations in
50 * capability mode -- for example, shm_open(2) is limited to creating
51 * anonymous, rather than named, POSIX shared memory objects.
52 */
53
54 #include "opt_capsicum.h"
55
56 #include <sys/cdefs.h>
57 __FBSDID("$FreeBSD: releng/9.2/sys/kern/sys_capability.c 234037 2012-04-08 16:26:26Z pho $");
58
59 #include <sys/param.h>
60 #include <sys/capability.h>
61 #include <sys/file.h>
62 #include <sys/filedesc.h>
63 #include <sys/kernel.h>
64 #include <sys/lock.h>
65 #include <sys/mutex.h>
66 #include <sys/proc.h>
67 #include <sys/sysproto.h>
68 #include <sys/sysctl.h>
69 #include <sys/systm.h>
70 #include <sys/ucred.h>
71
72 #include <security/audit/audit.h>
73
74 #include <vm/uma.h>
75 #include <vm/vm.h>
76
77 #ifdef CAPABILITY_MODE
78
79 FEATURE(security_capability_mode, "Capsicum Capability Mode");
80
81 /*
82 * System call to enter capability mode for the process.
83 */
84 int
85 sys_cap_enter(struct thread *td, struct cap_enter_args *uap)
86 {
87 struct ucred *newcred, *oldcred;
88 struct proc *p;
89
90 if (IN_CAPABILITY_MODE(td))
91 return (0);
92
93 newcred = crget();
94 p = td->td_proc;
95 PROC_LOCK(p);
96 oldcred = p->p_ucred;
97 crcopy(newcred, oldcred);
98 newcred->cr_flags |= CRED_FLAG_CAPMODE;
99 p->p_ucred = newcred;
100 PROC_UNLOCK(p);
101 crfree(oldcred);
102 return (0);
103 }
104
105 /*
106 * System call to query whether the process is in capability mode.
107 */
108 int
109 sys_cap_getmode(struct thread *td, struct cap_getmode_args *uap)
110 {
111 u_int i;
112
113 i = (IN_CAPABILITY_MODE(td)) ? 1 : 0;
114 return (copyout(&i, uap->modep, sizeof(i)));
115 }
116
117 #else /* !CAPABILITY_MODE */
118
119 int
120 sys_cap_enter(struct thread *td, struct cap_enter_args *uap)
121 {
122
123 return (ENOSYS);
124 }
125
126 int
127 sys_cap_getmode(struct thread *td, struct cap_getmode_args *uap)
128 {
129
130 return (ENOSYS);
131 }
132
133 #endif /* CAPABILITY_MODE */
134
135 #ifdef CAPABILITIES
136
137 FEATURE(security_capabilities, "Capsicum Capabilities");
138
139 /*
140 * struct capability describes a capability, and is hung off of its struct
141 * file f_data field. cap_file and cap_rightss are static once hooked up, as
142 * neither the object it references nor the rights it encapsulates are
143 * permitted to change.
144 */
145 struct capability {
146 struct file *cap_object; /* Underlying object's file. */
147 struct file *cap_file; /* Back-pointer to cap's file. */
148 cap_rights_t cap_rights; /* Mask of rights on object. */
149 };
150
151 /*
152 * Capabilities have a fileops vector, but in practice none should ever be
153 * called except for fo_close, as the capability will normally not be
154 * returned during a file descriptor lookup in the system call code.
155 */
156 static fo_rdwr_t capability_read;
157 static fo_rdwr_t capability_write;
158 static fo_truncate_t capability_truncate;
159 static fo_ioctl_t capability_ioctl;
160 static fo_poll_t capability_poll;
161 static fo_kqfilter_t capability_kqfilter;
162 static fo_stat_t capability_stat;
163 static fo_close_t capability_close;
164 static fo_chmod_t capability_chmod;
165 static fo_chown_t capability_chown;
166
167 static struct fileops capability_ops = {
168 .fo_read = capability_read,
169 .fo_write = capability_write,
170 .fo_truncate = capability_truncate,
171 .fo_ioctl = capability_ioctl,
172 .fo_poll = capability_poll,
173 .fo_kqfilter = capability_kqfilter,
174 .fo_stat = capability_stat,
175 .fo_close = capability_close,
176 .fo_chmod = capability_chmod,
177 .fo_chown = capability_chown,
178 .fo_flags = DFLAG_PASSABLE,
179 };
180
181 static struct fileops capability_ops_unpassable = {
182 .fo_read = capability_read,
183 .fo_write = capability_write,
184 .fo_truncate = capability_truncate,
185 .fo_ioctl = capability_ioctl,
186 .fo_poll = capability_poll,
187 .fo_kqfilter = capability_kqfilter,
188 .fo_stat = capability_stat,
189 .fo_close = capability_close,
190 .fo_chmod = capability_chmod,
191 .fo_chown = capability_chown,
192 .fo_flags = 0,
193 };
194
195 static uma_zone_t capability_zone;
196
197 static void
198 capability_init(void *dummy __unused)
199 {
200
201 capability_zone = uma_zcreate("capability", sizeof(struct capability),
202 NULL, NULL, NULL, NULL, UMA_ALIGN_PTR, 0);
203 if (capability_zone == NULL)
204 panic("capability_init: capability_zone not initialized");
205 }
206 SYSINIT(vfs, SI_SUB_VFS, SI_ORDER_ANY, capability_init, NULL);
207
208 /*
209 * Test whether a capability grants the requested rights.
210 */
211 static int
212 cap_check(struct capability *c, cap_rights_t rights)
213 {
214
215 if ((c->cap_rights | rights) != c->cap_rights)
216 return (ENOTCAPABLE);
217 return (0);
218 }
219
220 /*
221 * Extract rights from a capability for monitoring purposes -- not for use in
222 * any other way, as we want to keep all capability permission evaluation in
223 * this one file.
224 */
225 cap_rights_t
226 cap_rights(struct file *fp_cap)
227 {
228 struct capability *c;
229
230 KASSERT(fp_cap->f_type == DTYPE_CAPABILITY,
231 ("cap_rights: !capability"));
232
233 c = fp_cap->f_data;
234 return (c->cap_rights);
235 }
236
237 /*
238 * System call to create a new capability reference to either an existing
239 * file object or an an existing capability.
240 */
241 int
242 sys_cap_new(struct thread *td, struct cap_new_args *uap)
243 {
244 int error, capfd;
245 int fd = uap->fd;
246 struct file *fp;
247 cap_rights_t rights = uap->rights;
248
249 AUDIT_ARG_FD(fd);
250 AUDIT_ARG_RIGHTS(rights);
251 error = fget(td, fd, rights, &fp);
252 if (error)
253 return (error);
254 AUDIT_ARG_FILE(td->td_proc, fp);
255 error = kern_capwrap(td, fp, rights, &capfd);
256 /*
257 * Release our reference to the file (kern_capwrap has held a reference
258 * for the filedesc array).
259 */
260 fdrop(fp, td);
261 if (error == 0)
262 td->td_retval[0] = capfd;
263 return (error);
264 }
265
266 /*
267 * System call to query the rights mask associated with a capability.
268 */
269 int
270 sys_cap_getrights(struct thread *td, struct cap_getrights_args *uap)
271 {
272 struct capability *cp;
273 struct file *fp;
274 int error;
275
276 AUDIT_ARG_FD(uap->fd);
277 error = fgetcap(td, uap->fd, &fp);
278 if (error)
279 return (error);
280 cp = fp->f_data;
281 error = copyout(&cp->cap_rights, uap->rightsp, sizeof(*uap->rightsp));
282 fdrop(fp, td);
283 return (error);
284 }
285
286 /*
287 * Create a capability to wrap around an existing file.
288 */
289 int
290 kern_capwrap(struct thread *td, struct file *fp, cap_rights_t rights,
291 int *capfdp)
292 {
293 struct capability *cp, *cp_old;
294 struct file *fp_object, *fcapp;
295 int error;
296
297 if ((rights | CAP_MASK_VALID) != CAP_MASK_VALID)
298 return (EINVAL);
299
300 /*
301 * If a new capability is being derived from an existing capability,
302 * then the new capability rights must be a subset of the existing
303 * rights.
304 */
305 if (fp->f_type == DTYPE_CAPABILITY) {
306 cp_old = fp->f_data;
307 if ((cp_old->cap_rights | rights) != cp_old->cap_rights)
308 return (ENOTCAPABLE);
309 }
310
311 /*
312 * Allocate a new file descriptor to hang the capability off of.
313 */
314 error = falloc(td, &fcapp, capfdp, fp->f_flag);
315 if (error)
316 return (error);
317
318 /*
319 * Rather than nesting capabilities, directly reference the object an
320 * existing capability references. There's nothing else interesting
321 * to preserve for future use, as we've incorporated the previous
322 * rights mask into the new one. This prevents us from having to
323 * deal with capability chains.
324 */
325 if (fp->f_type == DTYPE_CAPABILITY)
326 fp_object = ((struct capability *)fp->f_data)->cap_object;
327 else
328 fp_object = fp;
329 fhold(fp_object);
330 cp = uma_zalloc(capability_zone, M_WAITOK | M_ZERO);
331 cp->cap_rights = rights;
332 cp->cap_object = fp_object;
333 cp->cap_file = fcapp;
334 if (fp->f_flag & DFLAG_PASSABLE)
335 finit(fcapp, fp->f_flag, DTYPE_CAPABILITY, cp,
336 &capability_ops);
337 else
338 finit(fcapp, fp->f_flag, DTYPE_CAPABILITY, cp,
339 &capability_ops_unpassable);
340
341 /*
342 * Release our private reference (the proc filedesc still has one).
343 */
344 fdrop(fcapp, td);
345 return (0);
346 }
347
348 /*
349 * Given a file descriptor, test it against a capability rights mask and then
350 * return the file descriptor on which to actually perform the requested
351 * operation. As long as the reference to fp_cap remains valid, the returned
352 * pointer in *fp will remain valid, so no extra reference management is
353 * required, and the caller should fdrop() fp_cap as normal when done with
354 * both.
355 */
356 int
357 cap_funwrap(struct file *fp_cap, cap_rights_t rights, struct file **fpp)
358 {
359 struct capability *c;
360 int error;
361
362 if (fp_cap->f_type != DTYPE_CAPABILITY) {
363 *fpp = fp_cap;
364 return (0);
365 }
366 c = fp_cap->f_data;
367 error = cap_check(c, rights);
368 if (error)
369 return (error);
370 *fpp = c->cap_object;
371 return (0);
372 }
373
374 /*
375 * Slightly different routine for memory mapping file descriptors: unwrap the
376 * capability and check CAP_MMAP, but also return a bitmask representing the
377 * maximum mapping rights the capability allows on the object.
378 */
379 int
380 cap_funwrap_mmap(struct file *fp_cap, cap_rights_t rights, u_char *maxprotp,
381 struct file **fpp)
382 {
383 struct capability *c;
384 u_char maxprot;
385 int error;
386
387 if (fp_cap->f_type != DTYPE_CAPABILITY) {
388 *fpp = fp_cap;
389 *maxprotp = VM_PROT_ALL;
390 return (0);
391 }
392 c = fp_cap->f_data;
393 error = cap_check(c, rights | CAP_MMAP);
394 if (error)
395 return (error);
396 *fpp = c->cap_object;
397 maxprot = 0;
398 if (c->cap_rights & CAP_READ)
399 maxprot |= VM_PROT_READ;
400 if (c->cap_rights & CAP_WRITE)
401 maxprot |= VM_PROT_WRITE;
402 if (c->cap_rights & CAP_MAPEXEC)
403 maxprot |= VM_PROT_EXECUTE;
404 *maxprotp = maxprot;
405 return (0);
406 }
407
408 /*
409 * When a capability is closed, simply drop the reference on the underlying
410 * object and free the capability. fdrop() will handle the case where the
411 * underlying object also needs to close, and the caller will have already
412 * performed any object-specific lock or mqueue handling.
413 */
414 static int
415 capability_close(struct file *fp, struct thread *td)
416 {
417 struct capability *c;
418 struct file *fp_object;
419
420 KASSERT(fp->f_type == DTYPE_CAPABILITY,
421 ("capability_close: !capability"));
422
423 c = fp->f_data;
424 fp->f_ops = &badfileops;
425 fp->f_data = NULL;
426 fp_object = c->cap_object;
427 uma_zfree(capability_zone, c);
428 return (fdrop(fp_object, td));
429 }
430
431 /*
432 * In general, file descriptor operations should never make it to the
433 * capability, only the underlying file descriptor operation vector, so panic
434 * if we do turn up here.
435 */
436 static int
437 capability_read(struct file *fp, struct uio *uio, struct ucred *active_cred,
438 int flags, struct thread *td)
439 {
440
441 panic("capability_read");
442 }
443
444 static int
445 capability_write(struct file *fp, struct uio *uio, struct ucred *active_cred,
446 int flags, struct thread *td)
447 {
448
449 panic("capability_write");
450 }
451
452 static int
453 capability_truncate(struct file *fp, off_t length, struct ucred *active_cred,
454 struct thread *td)
455 {
456
457 panic("capability_truncate");
458 }
459
460 static int
461 capability_ioctl(struct file *fp, u_long com, void *data,
462 struct ucred *active_cred, struct thread *td)
463 {
464
465 panic("capability_ioctl");
466 }
467
468 static int
469 capability_poll(struct file *fp, int events, struct ucred *active_cred,
470 struct thread *td)
471 {
472
473 panic("capability_poll");
474 }
475
476 static int
477 capability_kqfilter(struct file *fp, struct knote *kn)
478 {
479
480 panic("capability_kqfilter");
481 }
482
483 static int
484 capability_stat(struct file *fp, struct stat *sb, struct ucred *active_cred,
485 struct thread *td)
486 {
487
488 panic("capability_stat");
489 }
490
491 int
492 capability_chmod(struct file *fp, mode_t mode, struct ucred *active_cred,
493 struct thread *td)
494 {
495
496 panic("capability_chmod");
497 }
498
499 int
500 capability_chown(struct file *fp, uid_t uid, gid_t gid,
501 struct ucred *active_cred, struct thread *td)
502 {
503
504 panic("capability_chown");
505 }
506
507 #else /* !CAPABILITIES */
508
509 /*
510 * Stub Capability functions for when options CAPABILITIES isn't compiled
511 * into the kernel.
512 */
513 int
514 sys_cap_new(struct thread *td, struct cap_new_args *uap)
515 {
516
517 return (ENOSYS);
518 }
519
520 int
521 sys_cap_getrights(struct thread *td, struct cap_getrights_args *uap)
522 {
523
524 return (ENOSYS);
525 }
526
527 int
528 cap_funwrap(struct file *fp_cap, cap_rights_t rights, struct file **fpp)
529 {
530
531 KASSERT(fp_cap->f_type != DTYPE_CAPABILITY,
532 ("cap_funwrap: saw capability"));
533
534 *fpp = fp_cap;
535 return (0);
536 }
537
538 int
539 cap_funwrap_mmap(struct file *fp_cap, cap_rights_t rights, u_char *maxprotp,
540 struct file **fpp)
541 {
542
543 KASSERT(fp_cap->f_type != DTYPE_CAPABILITY,
544 ("cap_funwrap_mmap: saw capability"));
545
546 *fpp = fp_cap;
547 *maxprotp = VM_PROT_ALL;
548 return (0);
549 }
550
551 #endif /* CAPABILITIES */
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