2 * Copyright (c) 2012 Will Drewry <wad@dataspill.org>
4 * Permission to use, copy, modify, and distribute this software for any
5 * purpose with or without fee is hereby granted, provided that the above
6 * copyright notice and this permission notice appear in all copies.
8 * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
9 * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
10 * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
11 * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
12 * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
13 * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
14 * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
18 * Uncomment the SANDBOX_SECCOMP_FILTER_DEBUG macro below to help diagnose
19 * filter breakage during development. *Do not* use this in production,
20 * as it relies on making library calls that are unsafe in signal context.
22 * Instead, live systems the auditctl(8) may be used to monitor failures.
24 * auditctl -a task,always -F uid=<privsep uid>
26 /* #define SANDBOX_SECCOMP_FILTER_DEBUG 1 */
28 /* XXX it should be possible to do logging via the log socket safely */
30 #ifdef SANDBOX_SECCOMP_FILTER_DEBUG
31 /* Use the kernel headers in case of an older toolchain. */
32 # include <asm/siginfo.h>
33 # define __have_siginfo_t 1
34 # define __have_sigval_t 1
35 # define __have_sigevent_t 1
36 #endif /* SANDBOX_SECCOMP_FILTER_DEBUG */
40 #ifdef SANDBOX_SECCOMP_FILTER
42 #include <sys/types.h>
43 #include <sys/resource.h>
44 #include <sys/prctl.h>
46 #include <sys/syscall.h>
48 #include <linux/net.h>
49 #include <linux/audit.h>
50 #include <linux/filter.h>
51 #include <linux/seccomp.h>
54 #include <asm/unistd.h>
56 #include <asm/zcrypt.h>
62 #include <stddef.h> /* for offsetof */
69 #include "ssh-sandbox.h"
72 /* Linux seccomp_filter sandbox */
73 #define SECCOMP_FILTER_FAIL SECCOMP_RET_KILL
75 /* Use a signal handler to emit violations when debugging */
76 #ifdef SANDBOX_SECCOMP_FILTER_DEBUG
77 # undef SECCOMP_FILTER_FAIL
78 # define SECCOMP_FILTER_FAIL SECCOMP_RET_TRAP
79 #endif /* SANDBOX_SECCOMP_FILTER_DEBUG */
81 #if __BYTE_ORDER == __LITTLE_ENDIAN
82 # define ARG_LO_OFFSET 0
83 # define ARG_HI_OFFSET sizeof(uint32_t)
84 #elif __BYTE_ORDER == __BIG_ENDIAN
85 # define ARG_LO_OFFSET sizeof(uint32_t)
86 # define ARG_HI_OFFSET 0
88 #error "Unknown endianness"
91 /* Simple helpers to avoid manual errors (but larger BPF programs). */
92 #define SC_DENY(_nr, _errno) \
93 BPF_JUMP(BPF_JMP+BPF_JEQ+BPF_K, (_nr), 0, 1), \
94 BPF_STMT(BPF_RET+BPF_K, SECCOMP_RET_ERRNO|(_errno))
95 #define SC_ALLOW(_nr) \
96 BPF_JUMP(BPF_JMP+BPF_JEQ+BPF_K, (_nr), 0, 1), \
97 BPF_STMT(BPF_RET+BPF_K, SECCOMP_RET_ALLOW)
98 #define SC_ALLOW_ARG(_nr, _arg_nr, _arg_val) \
99 BPF_JUMP(BPF_JMP+BPF_JEQ+BPF_K, (_nr), 0, 6), \
100 /* load and test syscall argument, low word */ \
101 BPF_STMT(BPF_LD+BPF_W+BPF_ABS, \
102 offsetof(struct seccomp_data, args[(_arg_nr)]) + ARG_LO_OFFSET), \
103 BPF_JUMP(BPF_JMP+BPF_JEQ+BPF_K, \
104 ((_arg_val) & 0xFFFFFFFF), 0, 3), \
105 /* load and test syscall argument, high word */ \
106 BPF_STMT(BPF_LD+BPF_W+BPF_ABS, \
107 offsetof(struct seccomp_data, args[(_arg_nr)]) + ARG_HI_OFFSET), \
108 BPF_JUMP(BPF_JMP+BPF_JEQ+BPF_K, \
109 (((uint32_t)((uint64_t)(_arg_val) >> 32)) & 0xFFFFFFFF), 0, 1), \
110 BPF_STMT(BPF_RET+BPF_K, SECCOMP_RET_ALLOW), \
111 /* reload syscall number; all rules expect it in accumulator */ \
112 BPF_STMT(BPF_LD+BPF_W+BPF_ABS, \
113 offsetof(struct seccomp_data, nr))
114 /* Allow if syscall argument contains only values in mask */
115 #define SC_ALLOW_ARG_MASK(_nr, _arg_nr, _arg_mask) \
116 BPF_JUMP(BPF_JMP+BPF_JEQ+BPF_K, (_nr), 0, 8), \
117 /* load, mask and test syscall argument, low word */ \
118 BPF_STMT(BPF_LD+BPF_W+BPF_ABS, \
119 offsetof(struct seccomp_data, args[(_arg_nr)]) + ARG_LO_OFFSET), \
120 BPF_STMT(BPF_ALU+BPF_AND+BPF_K, ~((_arg_mask) & 0xFFFFFFFF)), \
121 BPF_JUMP(BPF_JMP+BPF_JEQ+BPF_K, 0, 0, 4), \
122 /* load, mask and test syscall argument, high word */ \
123 BPF_STMT(BPF_LD+BPF_W+BPF_ABS, \
124 offsetof(struct seccomp_data, args[(_arg_nr)]) + ARG_HI_OFFSET), \
125 BPF_STMT(BPF_ALU+BPF_AND+BPF_K, \
126 ~(((uint32_t)((uint64_t)(_arg_mask) >> 32)) & 0xFFFFFFFF)), \
127 BPF_JUMP(BPF_JMP+BPF_JEQ+BPF_K, 0, 0, 1), \
128 BPF_STMT(BPF_RET+BPF_K, SECCOMP_RET_ALLOW), \
129 /* reload syscall number; all rules expect it in accumulator */ \
130 BPF_STMT(BPF_LD+BPF_W+BPF_ABS, \
131 offsetof(struct seccomp_data, nr))
133 /* Syscall filtering set for preauth. */
134 static const struct sock_filter preauth_insns[] = {
135 /* Ensure the syscall arch convention is as expected. */
136 BPF_STMT(BPF_LD+BPF_W+BPF_ABS,
137 offsetof(struct seccomp_data, arch)),
138 BPF_JUMP(BPF_JMP+BPF_JEQ+BPF_K, SECCOMP_AUDIT_ARCH, 1, 0),
139 BPF_STMT(BPF_RET+BPF_K, SECCOMP_FILTER_FAIL),
140 /* Load the syscall number for checking. */
141 BPF_STMT(BPF_LD+BPF_W+BPF_ABS,
142 offsetof(struct seccomp_data, nr)),
144 /* Syscalls to non-fatally deny */
146 SC_DENY(__NR_lstat, EACCES),
149 SC_DENY(__NR_lstat64, EACCES),
152 SC_DENY(__NR_fstat, EACCES),
155 SC_DENY(__NR_fstat64, EACCES),
157 #ifdef __NR_fstatat64
158 SC_DENY(__NR_fstatat64, EACCES),
161 SC_DENY(__NR_open, EACCES),
164 SC_DENY(__NR_openat, EACCES),
166 #ifdef __NR_newfstatat
167 SC_DENY(__NR_newfstatat, EACCES),
170 SC_DENY(__NR_stat, EACCES),
173 SC_DENY(__NR_stat64, EACCES),
176 SC_DENY(__NR_shmget, EACCES),
179 SC_DENY(__NR_shmat, EACCES),
182 SC_DENY(__NR_shmdt, EACCES),
185 SC_DENY(__NR_ipc, EACCES),
188 SC_DENY(__NR_statx, EACCES),
191 /* Syscalls to permit */
195 #ifdef __NR_clock_gettime
196 SC_ALLOW(__NR_clock_gettime),
198 #ifdef __NR_clock_gettime64
199 SC_ALLOW(__NR_clock_gettime64),
202 SC_ALLOW(__NR_close),
207 #ifdef __NR_exit_group
208 SC_ALLOW(__NR_exit_group),
211 SC_ALLOW(__NR_futex),
213 #ifdef __NR_futex_time64
214 SC_ALLOW(__NR_futex_time64),
217 SC_ALLOW(__NR_geteuid),
219 #ifdef __NR_geteuid32
220 SC_ALLOW(__NR_geteuid32),
223 SC_ALLOW(__NR_getpgid),
226 SC_ALLOW(__NR_getpid),
228 #ifdef __NR_getrandom
229 SC_ALLOW(__NR_getrandom),
231 #ifdef __NR_gettimeofday
232 SC_ALLOW(__NR_gettimeofday),
235 SC_ALLOW(__NR_getuid),
238 SC_ALLOW(__NR_getuid32),
241 SC_ALLOW(__NR_madvise),
244 SC_ALLOW_ARG_MASK(__NR_mmap, 2, PROT_READ|PROT_WRITE|PROT_NONE),
247 SC_ALLOW_ARG_MASK(__NR_mmap2, 2, PROT_READ|PROT_WRITE|PROT_NONE),
250 SC_ALLOW_ARG_MASK(__NR_mprotect, 2, PROT_READ|PROT_WRITE|PROT_NONE),
253 SC_ALLOW(__NR_mremap),
256 SC_ALLOW(__NR_munmap),
258 #ifdef __NR_nanosleep
259 SC_ALLOW(__NR_nanosleep),
261 #ifdef __NR_clock_nanosleep
262 SC_ALLOW(__NR_clock_nanosleep),
264 #ifdef __NR_clock_nanosleep_time64
265 SC_ALLOW(__NR_clock_nanosleep_time64),
267 #ifdef __NR_clock_gettime64
268 SC_ALLOW(__NR_clock_gettime64),
270 #ifdef __NR__newselect
271 SC_ALLOW(__NR__newselect),
277 SC_ALLOW(__NR_pselect6),
279 #ifdef __NR_pselect6_time64
280 SC_ALLOW(__NR_pselect6_time64),
285 #ifdef __NR_rt_sigprocmask
286 SC_ALLOW(__NR_rt_sigprocmask),
289 SC_ALLOW(__NR_select),
292 SC_ALLOW(__NR_shutdown),
294 #ifdef __NR_sigprocmask
295 SC_ALLOW(__NR_sigprocmask),
301 SC_ALLOW(__NR_write),
303 #ifdef __NR_socketcall
304 SC_ALLOW_ARG(__NR_socketcall, 0, SYS_SHUTDOWN),
305 SC_DENY(__NR_socketcall, EACCES),
307 #if defined(__NR_ioctl) && defined(__s390__)
308 /* Allow ioctls for ICA crypto card on s390 */
309 SC_ALLOW_ARG(__NR_ioctl, 1, Z90STAT_STATUS_MASK),
310 SC_ALLOW_ARG(__NR_ioctl, 1, ICARSAMODEXPO),
311 SC_ALLOW_ARG(__NR_ioctl, 1, ICARSACRT),
312 SC_ALLOW_ARG(__NR_ioctl, 1, ZSECSENDCPRB),
313 /* Allow ioctls for EP11 crypto card on s390 */
314 SC_ALLOW_ARG(__NR_ioctl, 1, ZSENDEP11CPRB),
316 #if defined(__x86_64__) && defined(__ILP32__) && defined(__X32_SYSCALL_BIT)
318 * On Linux x32, the clock_gettime VDSO falls back to the
319 * x86-64 syscall under some circumstances, e.g.
320 * https://bugs.debian.org/849923
322 SC_ALLOW(__NR_clock_gettime & ~__X32_SYSCALL_BIT),
326 BPF_STMT(BPF_RET+BPF_K, SECCOMP_FILTER_FAIL),
329 static const struct sock_fprog preauth_program = {
330 .len = (unsigned short)(sizeof(preauth_insns)/sizeof(preauth_insns[0])),
331 .filter = (struct sock_filter *)preauth_insns,
339 ssh_sandbox_init(struct monitor *monitor)
341 struct ssh_sandbox *box;
344 * Strictly, we don't need to maintain any state here but we need
345 * to return non-NULL to satisfy the API.
347 debug3("%s: preparing seccomp filter sandbox", __func__);
348 box = xcalloc(1, sizeof(*box));
354 #ifdef SANDBOX_SECCOMP_FILTER_DEBUG
355 extern struct monitor *pmonitor;
356 void mm_log_handler(LogLevel level, const char *msg, void *ctx);
359 ssh_sandbox_violation(int signum, siginfo_t *info, void *void_context)
363 snprintf(msg, sizeof(msg),
364 "%s: unexpected system call (arch:0x%x,syscall:%d @ %p)",
365 __func__, info->si_arch, info->si_syscall, info->si_call_addr);
366 mm_log_handler(SYSLOG_LEVEL_FATAL, msg, pmonitor);
371 ssh_sandbox_child_debugging(void)
373 struct sigaction act;
376 debug3("%s: installing SIGSYS handler", __func__);
377 memset(&act, 0, sizeof(act));
379 sigaddset(&mask, SIGSYS);
381 act.sa_sigaction = &ssh_sandbox_violation;
382 act.sa_flags = SA_SIGINFO;
383 if (sigaction(SIGSYS, &act, NULL) == -1)
384 fatal("%s: sigaction(SIGSYS): %s", __func__, strerror(errno));
385 if (sigprocmask(SIG_UNBLOCK, &mask, NULL) == -1)
386 fatal("%s: sigprocmask(SIGSYS): %s",
387 __func__, strerror(errno));
389 #endif /* SANDBOX_SECCOMP_FILTER_DEBUG */
392 ssh_sandbox_child(struct ssh_sandbox *box)
394 struct rlimit rl_zero;
397 /* Set rlimits for completeness if possible. */
398 rl_zero.rlim_cur = rl_zero.rlim_max = 0;
399 if (setrlimit(RLIMIT_FSIZE, &rl_zero) == -1)
400 fatal("%s: setrlimit(RLIMIT_FSIZE, { 0, 0 }): %s",
401 __func__, strerror(errno));
402 if (setrlimit(RLIMIT_NOFILE, &rl_zero) == -1)
403 fatal("%s: setrlimit(RLIMIT_NOFILE, { 0, 0 }): %s",
404 __func__, strerror(errno));
405 if (setrlimit(RLIMIT_NPROC, &rl_zero) == -1)
406 fatal("%s: setrlimit(RLIMIT_NPROC, { 0, 0 }): %s",
407 __func__, strerror(errno));
409 #ifdef SANDBOX_SECCOMP_FILTER_DEBUG
410 ssh_sandbox_child_debugging();
411 #endif /* SANDBOX_SECCOMP_FILTER_DEBUG */
413 debug3("%s: setting PR_SET_NO_NEW_PRIVS", __func__);
414 if (prctl(PR_SET_NO_NEW_PRIVS, 1, 0, 0, 0) == -1) {
415 debug("%s: prctl(PR_SET_NO_NEW_PRIVS): %s",
416 __func__, strerror(errno));
419 debug3("%s: attaching seccomp filter program", __func__);
420 if (prctl(PR_SET_SECCOMP, SECCOMP_MODE_FILTER, &preauth_program) == -1)
421 debug("%s: prctl(PR_SET_SECCOMP): %s",
422 __func__, strerror(errno));
424 fatal("%s: SECCOMP_MODE_FILTER activated but "
425 "PR_SET_NO_NEW_PRIVS failed", __func__);
429 ssh_sandbox_parent_finish(struct ssh_sandbox *box)
432 debug3("%s: finished", __func__);
436 ssh_sandbox_parent_preauth(struct ssh_sandbox *box, pid_t child_pid)
438 box->child_pid = child_pid;
441 #endif /* SANDBOX_SECCOMP_FILTER */