2 * Copyright (c) 2008-2011 Robert N. M. Watson
3 * Copyright (c) 2010-2011 Jonathan Anderson
6 * This software was developed at the University of Cambridge Computer
7 * Laboratory with support from a grant from Google, Inc.
9 * Redistribution and use in source and binary forms, with or without
10 * modification, are permitted provided that the following conditions
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.
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
32 * FreeBSD kernel capability facility.
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.
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.
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.
54 #include "opt_capsicum.h"
56 #include <sys/cdefs.h>
57 __FBSDID("$FreeBSD$");
59 #include <sys/param.h>
60 #include <sys/capability.h>
62 #include <sys/filedesc.h>
63 #include <sys/kernel.h>
65 #include <sys/mutex.h>
67 #include <sys/sysproto.h>
68 #include <sys/sysctl.h>
69 #include <sys/systm.h>
70 #include <sys/ucred.h>
72 #include <security/audit/audit.h>
77 #ifdef CAPABILITY_MODE
79 FEATURE(security_capability_mode, "Capsicum Capability Mode");
82 * System call to enter capability mode for the process.
85 sys_cap_enter(struct thread *td, struct cap_enter_args *uap)
87 struct ucred *newcred, *oldcred;
90 if (IN_CAPABILITY_MODE(td))
97 crcopy(newcred, oldcred);
98 newcred->cr_flags |= CRED_FLAG_CAPMODE;
106 * System call to query whether the process is in capability mode.
109 sys_cap_getmode(struct thread *td, struct cap_getmode_args *uap)
113 i = (IN_CAPABILITY_MODE(td)) ? 1 : 0;
114 return (copyout(&i, uap->modep, sizeof(i)));
117 #else /* !CAPABILITY_MODE */
120 sys_cap_enter(struct thread *td, struct cap_enter_args *uap)
127 sys_cap_getmode(struct thread *td, struct cap_getmode_args *uap)
133 #endif /* CAPABILITY_MODE */
137 FEATURE(security_capabilities, "Capsicum Capabilities");
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.
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. */
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.
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;
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,
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,
195 static uma_zone_t capability_zone;
198 capability_init(void *dummy __unused)
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");
206 SYSINIT(vfs, SI_SUB_VFS, SI_ORDER_ANY, capability_init, NULL);
209 * Test whether a capability grants the requested rights.
212 cap_check(struct capability *c, cap_rights_t rights)
215 if ((c->cap_rights | rights) != c->cap_rights)
216 return (ENOTCAPABLE);
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
226 cap_rights(struct file *fp_cap)
228 struct capability *c;
230 KASSERT(fp_cap->f_type == DTYPE_CAPABILITY,
231 ("cap_rights: !capability"));
234 return (c->cap_rights);
238 * System call to create a new capability reference to either an existing
239 * file object or an an existing capability.
242 sys_cap_new(struct thread *td, struct cap_new_args *uap)
247 cap_rights_t rights = uap->rights;
250 AUDIT_ARG_RIGHTS(rights);
251 error = fget(td, fd, rights, &fp);
254 AUDIT_ARG_FILE(td->td_proc, fp);
255 error = kern_capwrap(td, fp, rights, &capfd);
257 * Release our reference to the file (kern_capwrap has held a reference
258 * for the filedesc array).
262 td->td_retval[0] = capfd;
267 * System call to query the rights mask associated with a capability.
270 sys_cap_getrights(struct thread *td, struct cap_getrights_args *uap)
272 struct capability *cp;
276 AUDIT_ARG_FD(uap->fd);
277 error = fgetcap(td, uap->fd, &fp);
281 error = copyout(&cp->cap_rights, uap->rightsp, sizeof(*uap->rightsp));
287 * Create a capability to wrap around an existing file.
290 kern_capwrap(struct thread *td, struct file *fp, cap_rights_t rights,
293 struct capability *cp, *cp_old;
294 struct file *fp_object, *fcapp;
297 if ((rights | CAP_MASK_VALID) != CAP_MASK_VALID)
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
305 if (fp->f_type == DTYPE_CAPABILITY) {
307 if ((cp_old->cap_rights | rights) != cp_old->cap_rights)
308 return (ENOTCAPABLE);
312 * Allocate a new file descriptor to hang the capability off of.
314 error = falloc(td, &fcapp, capfdp, fp->f_flag);
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.
325 if (fp->f_type == DTYPE_CAPABILITY)
326 fp_object = ((struct capability *)fp->f_data)->cap_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,
338 finit(fcapp, fp->f_flag, DTYPE_CAPABILITY, cp,
339 &capability_ops_unpassable);
342 * Release our private reference (the proc filedesc still has one).
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
357 cap_funwrap(struct file *fp_cap, cap_rights_t rights, struct file **fpp)
359 struct capability *c;
362 if (fp_cap->f_type != DTYPE_CAPABILITY) {
367 error = cap_check(c, rights);
370 *fpp = c->cap_object;
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.
380 cap_funwrap_mmap(struct file *fp_cap, cap_rights_t rights, u_char *maxprotp,
383 struct capability *c;
387 if (fp_cap->f_type != DTYPE_CAPABILITY) {
389 *maxprotp = VM_PROT_ALL;
393 error = cap_check(c, rights | CAP_MMAP);
396 *fpp = c->cap_object;
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;
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.
415 capability_close(struct file *fp, struct thread *td)
417 struct capability *c;
418 struct file *fp_object;
420 KASSERT(fp->f_type == DTYPE_CAPABILITY,
421 ("capability_close: !capability"));
424 fp->f_ops = &badfileops;
426 fp_object = c->cap_object;
427 uma_zfree(capability_zone, c);
428 return (fdrop(fp_object, td));
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.
437 capability_read(struct file *fp, struct uio *uio, struct ucred *active_cred,
438 int flags, struct thread *td)
441 panic("capability_read");
445 capability_write(struct file *fp, struct uio *uio, struct ucred *active_cred,
446 int flags, struct thread *td)
449 panic("capability_write");
453 capability_truncate(struct file *fp, off_t length, struct ucred *active_cred,
457 panic("capability_truncate");
461 capability_ioctl(struct file *fp, u_long com, void *data,
462 struct ucred *active_cred, struct thread *td)
465 panic("capability_ioctl");
469 capability_poll(struct file *fp, int events, struct ucred *active_cred,
473 panic("capability_poll");
477 capability_kqfilter(struct file *fp, struct knote *kn)
480 panic("capability_kqfilter");
484 capability_stat(struct file *fp, struct stat *sb, struct ucred *active_cred,
488 panic("capability_stat");
492 capability_chmod(struct file *fp, mode_t mode, struct ucred *active_cred,
496 panic("capability_chmod");
500 capability_chown(struct file *fp, uid_t uid, gid_t gid,
501 struct ucred *active_cred, struct thread *td)
504 panic("capability_chown");
507 #else /* !CAPABILITIES */
510 * Stub Capability functions for when options CAPABILITIES isn't compiled
514 sys_cap_new(struct thread *td, struct cap_new_args *uap)
521 sys_cap_getrights(struct thread *td, struct cap_getrights_args *uap)
528 cap_funwrap(struct file *fp_cap, cap_rights_t rights, struct file **fpp)
531 KASSERT(fp_cap->f_type != DTYPE_CAPABILITY,
532 ("cap_funwrap: saw capability"));
539 cap_funwrap_mmap(struct file *fp_cap, cap_rights_t rights, u_char *maxprotp,
543 KASSERT(fp_cap->f_type != DTYPE_CAPABILITY,
544 ("cap_funwrap_mmap: saw capability"));
547 *maxprotp = VM_PROT_ALL;
551 #endif /* CAPABILITIES */