freebsd-skq/sys/kern/sys_capability.c
Mark Johnston 2d896b816b Enter a write sequence when updating rights.
The Capsicum system calls modify file descriptor table entries.  To
ensure that readers observe a consistent snapshot of descriptor writes,
the system calls need to signal to unlocked readers that an update is
pending.

Note that ioctl rights are always checked with the descriptor table lock
held, so it is not strictly necessary to signal unlocked readers.
However, we probably want to enable lockless ioctl checks eventually, so
use seqc_write_begin() in kern_cap_ioctls_limit() too.

Reviewed by:	kib
MFC after:	2 weeks
Sponsored by:	The FreeBSD Foundation
Differential Revision:	https://reviews.freebsd.org/D24119
2020-03-19 15:39:45 +00:00

690 lines
15 KiB
C

/*-
* SPDX-License-Identifier: BSD-2-Clause-FreeBSD
*
* Copyright (c) 2008-2011 Robert N. M. Watson
* Copyright (c) 2010-2011 Jonathan Anderson
* Copyright (c) 2012 FreeBSD Foundation
* All rights reserved.
*
* This software was developed at the University of Cambridge Computer
* Laboratory with support from a grant from Google, Inc.
*
* Portions of this software were developed by Pawel Jakub Dawidek under
* sponsorship from the FreeBSD Foundation.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
* 1. Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
* 2. Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in the
* documentation and/or other materials provided with the distribution.
*
* THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
* ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
* ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
* FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
* DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
* OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
* HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
* LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
* OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
* SUCH DAMAGE.
*/
/*
* FreeBSD kernel capability facility.
*
* Two kernel features are implemented here: capability mode, a sandboxed mode
* of execution for processes, and capabilities, a refinement on file
* descriptors that allows fine-grained control over operations on the file
* descriptor. Collectively, these allow processes to run in the style of a
* historic "capability system" in which they can use only resources
* explicitly delegated to them. This model is enforced by restricting access
* to global namespaces in capability mode.
*
* Capabilities wrap other file descriptor types, binding them to a constant
* rights mask set when the capability is created. New capabilities may be
* derived from existing capabilities, but only if they have the same or a
* strict subset of the rights on the original capability.
*
* System calls permitted in capability mode are defined in capabilities.conf;
* calls must be carefully audited for safety to ensure that they don't allow
* escape from a sandbox. Some calls permit only a subset of operations in
* capability mode -- for example, shm_open(2) is limited to creating
* anonymous, rather than named, POSIX shared memory objects.
*/
#include <sys/cdefs.h>
__FBSDID("$FreeBSD$");
#include "opt_capsicum.h"
#include "opt_ktrace.h"
#include <sys/param.h>
#include <sys/capsicum.h>
#include <sys/file.h>
#include <sys/filedesc.h>
#include <sys/kernel.h>
#include <sys/limits.h>
#include <sys/lock.h>
#include <sys/mutex.h>
#include <sys/proc.h>
#include <sys/syscallsubr.h>
#include <sys/sysproto.h>
#include <sys/sysctl.h>
#include <sys/systm.h>
#include <sys/ucred.h>
#include <sys/uio.h>
#include <sys/ktrace.h>
#include <security/audit/audit.h>
#include <vm/uma.h>
#include <vm/vm.h>
bool __read_frequently trap_enotcap;
SYSCTL_BOOL(_kern, OID_AUTO, trap_enotcap, CTLFLAG_RWTUN, &trap_enotcap, 0,
"Deliver SIGTRAP on ENOTCAPABLE");
#ifdef CAPABILITY_MODE
#define IOCTLS_MAX_COUNT 256 /* XXX: Is 256 sane? */
FEATURE(security_capability_mode, "Capsicum Capability Mode");
/*
* System call to enter capability mode for the process.
*/
int
sys_cap_enter(struct thread *td, struct cap_enter_args *uap)
{
struct ucred *newcred, *oldcred;
struct proc *p;
if (IN_CAPABILITY_MODE(td))
return (0);
newcred = crget();
p = td->td_proc;
PROC_LOCK(p);
oldcred = crcopysafe(p, newcred);
newcred->cr_flags |= CRED_FLAG_CAPMODE;
proc_set_cred(p, newcred);
PROC_UNLOCK(p);
crfree(oldcred);
return (0);
}
/*
* System call to query whether the process is in capability mode.
*/
int
sys_cap_getmode(struct thread *td, struct cap_getmode_args *uap)
{
u_int i;
i = IN_CAPABILITY_MODE(td) ? 1 : 0;
return (copyout(&i, uap->modep, sizeof(i)));
}
#else /* !CAPABILITY_MODE */
int
sys_cap_enter(struct thread *td, struct cap_enter_args *uap)
{
return (ENOSYS);
}
int
sys_cap_getmode(struct thread *td, struct cap_getmode_args *uap)
{
return (ENOSYS);
}
#endif /* CAPABILITY_MODE */
#ifdef CAPABILITIES
FEATURE(security_capabilities, "Capsicum Capabilities");
MALLOC_DECLARE(M_FILECAPS);
static inline int
_cap_check(const cap_rights_t *havep, const cap_rights_t *needp,
enum ktr_cap_fail_type type)
{
if (!cap_rights_contains(havep, needp)) {
#ifdef KTRACE
if (KTRPOINT(curthread, KTR_CAPFAIL))
ktrcapfail(type, needp, havep);
#endif
return (ENOTCAPABLE);
}
return (0);
}
/*
* Test whether a capability grants the requested rights.
*/
int
cap_check(const cap_rights_t *havep, const cap_rights_t *needp)
{
return (_cap_check(havep, needp, CAPFAIL_NOTCAPABLE));
}
int
cap_check_failed_notcapable(const cap_rights_t *havep, const cap_rights_t *needp)
{
#ifdef KTRACE
if (KTRPOINT(curthread, KTR_CAPFAIL))
ktrcapfail(CAPFAIL_NOTCAPABLE, needp, havep);
#endif
return (ENOTCAPABLE);
}
/*
* Convert capability rights into VM access flags.
*/
vm_prot_t
cap_rights_to_vmprot(const cap_rights_t *havep)
{
vm_prot_t maxprot;
maxprot = VM_PROT_NONE;
if (cap_rights_is_set(havep, CAP_MMAP_R))
maxprot |= VM_PROT_READ;
if (cap_rights_is_set(havep, CAP_MMAP_W))
maxprot |= VM_PROT_WRITE;
if (cap_rights_is_set(havep, CAP_MMAP_X))
maxprot |= VM_PROT_EXECUTE;
return (maxprot);
}
/*
* Extract rights from a capability for monitoring purposes -- not for use in
* any other way, as we want to keep all capability permission evaluation in
* this one file.
*/
const cap_rights_t *
cap_rights_fde(const struct filedescent *fdep)
{
return (cap_rights_fde_inline(fdep));
}
const cap_rights_t *
cap_rights(struct filedesc *fdp, int fd)
{
return (cap_rights_fde(&fdp->fd_ofiles[fd]));
}
int
kern_cap_rights_limit(struct thread *td, int fd, cap_rights_t *rights)
{
struct filedesc *fdp;
struct filedescent *fdep;
u_long *ioctls;
int error;
fdp = td->td_proc->p_fd;
FILEDESC_XLOCK(fdp);
fdep = fdeget_locked(fdp, fd);
if (fdep == NULL) {
FILEDESC_XUNLOCK(fdp);
return (EBADF);
}
ioctls = NULL;
error = _cap_check(cap_rights(fdp, fd), rights, CAPFAIL_INCREASE);
if (error == 0) {
seqc_write_begin(&fdep->fde_seqc);
fdep->fde_rights = *rights;
if (!cap_rights_is_set(rights, CAP_IOCTL)) {
ioctls = fdep->fde_ioctls;
fdep->fde_ioctls = NULL;
fdep->fde_nioctls = 0;
}
if (!cap_rights_is_set(rights, CAP_FCNTL))
fdep->fde_fcntls = 0;
seqc_write_end(&fdep->fde_seqc);
}
FILEDESC_XUNLOCK(fdp);
free(ioctls, M_FILECAPS);
return (error);
}
/*
* System call to limit rights of the given capability.
*/
int
sys_cap_rights_limit(struct thread *td, struct cap_rights_limit_args *uap)
{
cap_rights_t rights;
int error, version;
cap_rights_init_zero(&rights);
error = copyin(uap->rightsp, &rights, sizeof(rights.cr_rights[0]));
if (error != 0)
return (error);
version = CAPVER(&rights);
if (version != CAP_RIGHTS_VERSION_00)
return (EINVAL);
error = copyin(uap->rightsp, &rights,
sizeof(rights.cr_rights[0]) * CAPARSIZE(&rights));
if (error != 0)
return (error);
/* Check for race. */
if (CAPVER(&rights) != version)
return (EINVAL);
if (!cap_rights_is_valid(&rights))
return (EINVAL);
if (version != CAP_RIGHTS_VERSION) {
rights.cr_rights[0] &= ~(0x3ULL << 62);
rights.cr_rights[0] |= ((uint64_t)CAP_RIGHTS_VERSION << 62);
}
#ifdef KTRACE
if (KTRPOINT(td, KTR_STRUCT))
ktrcaprights(&rights);
#endif
AUDIT_ARG_FD(uap->fd);
AUDIT_ARG_RIGHTS(&rights);
return (kern_cap_rights_limit(td, uap->fd, &rights));
}
/*
* System call to query the rights mask associated with a capability.
*/
int
sys___cap_rights_get(struct thread *td, struct __cap_rights_get_args *uap)
{
struct filedesc *fdp;
cap_rights_t rights;
int error, fd, i, n;
if (uap->version != CAP_RIGHTS_VERSION_00)
return (EINVAL);
fd = uap->fd;
AUDIT_ARG_FD(fd);
fdp = td->td_proc->p_fd;
FILEDESC_SLOCK(fdp);
if (fget_locked(fdp, fd) == NULL) {
FILEDESC_SUNLOCK(fdp);
return (EBADF);
}
rights = *cap_rights(fdp, fd);
FILEDESC_SUNLOCK(fdp);
n = uap->version + 2;
if (uap->version != CAPVER(&rights)) {
/*
* For older versions we need to check if the descriptor
* doesn't contain rights not understood by the caller.
* If it does, we have to return an error.
*/
for (i = n; i < CAPARSIZE(&rights); i++) {
if ((rights.cr_rights[i] & ~(0x7FULL << 57)) != 0)
return (EINVAL);
}
}
error = copyout(&rights, uap->rightsp, sizeof(rights.cr_rights[0]) * n);
#ifdef KTRACE
if (error == 0 && KTRPOINT(td, KTR_STRUCT))
ktrcaprights(&rights);
#endif
return (error);
}
/*
* Test whether a capability grants the given ioctl command.
* If descriptor doesn't have CAP_IOCTL, then ioctls list is empty and
* ENOTCAPABLE will be returned.
*/
int
cap_ioctl_check(struct filedesc *fdp, int fd, u_long cmd)
{
struct filedescent *fdep;
u_long *cmds;
ssize_t ncmds;
long i;
KASSERT(fd >= 0 && fd < fdp->fd_nfiles,
("%s: invalid fd=%d", __func__, fd));
fdep = fdeget_locked(fdp, fd);
KASSERT(fdep != NULL,
("%s: invalid fd=%d", __func__, fd));
ncmds = fdep->fde_nioctls;
if (ncmds == -1)
return (0);
cmds = fdep->fde_ioctls;
for (i = 0; i < ncmds; i++) {
if (cmds[i] == cmd)
return (0);
}
return (ENOTCAPABLE);
}
/*
* Check if the current ioctls list can be replaced by the new one.
*/
static int
cap_ioctl_limit_check(struct filedescent *fdep, const u_long *cmds,
size_t ncmds)
{
u_long *ocmds;
ssize_t oncmds;
u_long i;
long j;
oncmds = fdep->fde_nioctls;
if (oncmds == -1)
return (0);
if (oncmds < (ssize_t)ncmds)
return (ENOTCAPABLE);
ocmds = fdep->fde_ioctls;
for (i = 0; i < ncmds; i++) {
for (j = 0; j < oncmds; j++) {
if (cmds[i] == ocmds[j])
break;
}
if (j == oncmds)
return (ENOTCAPABLE);
}
return (0);
}
int
kern_cap_ioctls_limit(struct thread *td, int fd, u_long *cmds, size_t ncmds)
{
struct filedesc *fdp;
struct filedescent *fdep;
u_long *ocmds;
int error;
AUDIT_ARG_FD(fd);
if (ncmds > IOCTLS_MAX_COUNT) {
error = EINVAL;
goto out_free;
}
fdp = td->td_proc->p_fd;
FILEDESC_XLOCK(fdp);
fdep = fdeget_locked(fdp, fd);
if (fdep == NULL) {
error = EBADF;
goto out;
}
error = cap_ioctl_limit_check(fdep, cmds, ncmds);
if (error != 0)
goto out;
ocmds = fdep->fde_ioctls;
seqc_write_begin(&fdep->fde_seqc);
fdep->fde_ioctls = cmds;
fdep->fde_nioctls = ncmds;
seqc_write_end(&fdep->fde_seqc);
cmds = ocmds;
error = 0;
out:
FILEDESC_XUNLOCK(fdp);
out_free:
free(cmds, M_FILECAPS);
return (error);
}
int
sys_cap_ioctls_limit(struct thread *td, struct cap_ioctls_limit_args *uap)
{
u_long *cmds;
size_t ncmds;
int error;
ncmds = uap->ncmds;
if (ncmds > IOCTLS_MAX_COUNT)
return (EINVAL);
if (ncmds == 0) {
cmds = NULL;
} else {
cmds = malloc(sizeof(cmds[0]) * ncmds, M_FILECAPS, M_WAITOK);
error = copyin(uap->cmds, cmds, sizeof(cmds[0]) * ncmds);
if (error != 0) {
free(cmds, M_FILECAPS);
return (error);
}
}
return (kern_cap_ioctls_limit(td, uap->fd, cmds, ncmds));
}
int
sys_cap_ioctls_get(struct thread *td, struct cap_ioctls_get_args *uap)
{
struct filedesc *fdp;
struct filedescent *fdep;
u_long *cmdsp, *dstcmds;
size_t maxcmds, ncmds;
int16_t count;
int error, fd;
fd = uap->fd;
dstcmds = uap->cmds;
maxcmds = uap->maxcmds;
AUDIT_ARG_FD(fd);
fdp = td->td_proc->p_fd;
cmdsp = NULL;
if (dstcmds != NULL) {
cmdsp = malloc(sizeof(cmdsp[0]) * IOCTLS_MAX_COUNT, M_FILECAPS,
M_WAITOK | M_ZERO);
}
FILEDESC_SLOCK(fdp);
fdep = fdeget_locked(fdp, fd);
if (fdep == NULL) {
error = EBADF;
FILEDESC_SUNLOCK(fdp);
goto out;
}
count = fdep->fde_nioctls;
if (count != -1 && cmdsp != NULL) {
ncmds = MIN(count, maxcmds);
memcpy(cmdsp, fdep->fde_ioctls, sizeof(cmdsp[0]) * ncmds);
}
FILEDESC_SUNLOCK(fdp);
/*
* If all ioctls are allowed (fde_nioctls == -1 && fde_ioctls == NULL)
* the only sane thing we can do is to not populate the given array and
* return CAP_IOCTLS_ALL.
*/
if (count != -1) {
if (cmdsp != NULL) {
error = copyout(cmdsp, dstcmds,
sizeof(cmdsp[0]) * ncmds);
if (error != 0)
goto out;
}
td->td_retval[0] = count;
} else {
td->td_retval[0] = CAP_IOCTLS_ALL;
}
error = 0;
out:
free(cmdsp, M_FILECAPS);
return (error);
}
/*
* Test whether a capability grants the given fcntl command.
*/
int
cap_fcntl_check_fde(struct filedescent *fdep, int cmd)
{
uint32_t fcntlcap;
fcntlcap = (1 << cmd);
KASSERT((CAP_FCNTL_ALL & fcntlcap) != 0,
("Unsupported fcntl=%d.", cmd));
if ((fdep->fde_fcntls & fcntlcap) != 0)
return (0);
return (ENOTCAPABLE);
}
int
cap_fcntl_check(struct filedesc *fdp, int fd, int cmd)
{
KASSERT(fd >= 0 && fd < fdp->fd_nfiles,
("%s: invalid fd=%d", __func__, fd));
return (cap_fcntl_check_fde(&fdp->fd_ofiles[fd], cmd));
}
int
sys_cap_fcntls_limit(struct thread *td, struct cap_fcntls_limit_args *uap)
{
struct filedesc *fdp;
struct filedescent *fdep;
uint32_t fcntlrights;
int fd;
fd = uap->fd;
fcntlrights = uap->fcntlrights;
AUDIT_ARG_FD(fd);
AUDIT_ARG_FCNTL_RIGHTS(fcntlrights);
if ((fcntlrights & ~CAP_FCNTL_ALL) != 0)
return (EINVAL);
fdp = td->td_proc->p_fd;
FILEDESC_XLOCK(fdp);
fdep = fdeget_locked(fdp, fd);
if (fdep == NULL) {
FILEDESC_XUNLOCK(fdp);
return (EBADF);
}
if ((fcntlrights & ~fdep->fde_fcntls) != 0) {
FILEDESC_XUNLOCK(fdp);
return (ENOTCAPABLE);
}
seqc_write_begin(&fdep->fde_seqc);
fdep->fde_fcntls = fcntlrights;
seqc_write_end(&fdep->fde_seqc);
FILEDESC_XUNLOCK(fdp);
return (0);
}
int
sys_cap_fcntls_get(struct thread *td, struct cap_fcntls_get_args *uap)
{
struct filedesc *fdp;
struct filedescent *fdep;
uint32_t rights;
int fd;
fd = uap->fd;
AUDIT_ARG_FD(fd);
fdp = td->td_proc->p_fd;
FILEDESC_SLOCK(fdp);
fdep = fdeget_locked(fdp, fd);
if (fdep == NULL) {
FILEDESC_SUNLOCK(fdp);
return (EBADF);
}
rights = fdep->fde_fcntls;
FILEDESC_SUNLOCK(fdp);
return (copyout(&rights, uap->fcntlrightsp, sizeof(rights)));
}
#else /* !CAPABILITIES */
/*
* Stub Capability functions for when options CAPABILITIES isn't compiled
* into the kernel.
*/
int
sys_cap_rights_limit(struct thread *td, struct cap_rights_limit_args *uap)
{
return (ENOSYS);
}
int
sys___cap_rights_get(struct thread *td, struct __cap_rights_get_args *uap)
{
return (ENOSYS);
}
int
sys_cap_ioctls_limit(struct thread *td, struct cap_ioctls_limit_args *uap)
{
return (ENOSYS);
}
int
sys_cap_ioctls_get(struct thread *td, struct cap_ioctls_get_args *uap)
{
return (ENOSYS);
}
int
sys_cap_fcntls_limit(struct thread *td, struct cap_fcntls_limit_args *uap)
{
return (ENOSYS);
}
int
sys_cap_fcntls_get(struct thread *td, struct cap_fcntls_get_args *uap)
{
return (ENOSYS);
}
#endif /* CAPABILITIES */