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 <linux/net.h>
47 #include <linux/audit.h>
48 #include <linux/filter.h>
49 #include <linux/seccomp.h>
52 #include <asm/unistd.h>
54 #include <asm/zcrypt.h>
60 #include <stddef.h> /* for offsetof */
67 #include "ssh-sandbox.h"
70 /* Linux seccomp_filter sandbox */
71 #define SECCOMP_FILTER_FAIL SECCOMP_RET_KILL
73 /* Use a signal handler to emit violations when debugging */
74 #ifdef SANDBOX_SECCOMP_FILTER_DEBUG
75 # undef SECCOMP_FILTER_FAIL
76 # define SECCOMP_FILTER_FAIL SECCOMP_RET_TRAP
77 #endif /* SANDBOX_SECCOMP_FILTER_DEBUG */
79 #if __BYTE_ORDER == __LITTLE_ENDIAN
80 # define ARG_LO_OFFSET 0
81 # define ARG_HI_OFFSET sizeof(uint32_t)
82 #elif __BYTE_ORDER == __BIG_ENDIAN
83 # define ARG_LO_OFFSET sizeof(uint32_t)
84 # define ARG_HI_OFFSET 0
86 #error "Unknown endianness"
89 /* Simple helpers to avoid manual errors (but larger BPF programs). */
90 #define SC_DENY(_nr, _errno) \
91 BPF_JUMP(BPF_JMP+BPF_JEQ+BPF_K, (_nr), 0, 1), \
92 BPF_STMT(BPF_RET+BPF_K, SECCOMP_RET_ERRNO|(_errno))
93 #define SC_ALLOW(_nr) \
94 BPF_JUMP(BPF_JMP+BPF_JEQ+BPF_K, (_nr), 0, 1), \
95 BPF_STMT(BPF_RET+BPF_K, SECCOMP_RET_ALLOW)
96 #define SC_ALLOW_ARG(_nr, _arg_nr, _arg_val) \
97 BPF_JUMP(BPF_JMP+BPF_JEQ+BPF_K, (_nr), 0, 6), \
98 /* load and test first syscall argument, low word */ \
99 BPF_STMT(BPF_LD+BPF_W+BPF_ABS, \
100 offsetof(struct seccomp_data, args[(_arg_nr)]) + ARG_LO_OFFSET), \
101 BPF_JUMP(BPF_JMP+BPF_JEQ+BPF_K, \
102 ((_arg_val) & 0xFFFFFFFF), 0, 3), \
103 /* load and test first syscall argument, high word */ \
104 BPF_STMT(BPF_LD+BPF_W+BPF_ABS, \
105 offsetof(struct seccomp_data, args[(_arg_nr)]) + ARG_HI_OFFSET), \
106 BPF_JUMP(BPF_JMP+BPF_JEQ+BPF_K, \
107 (((uint32_t)((uint64_t)(_arg_val) >> 32)) & 0xFFFFFFFF), 0, 1), \
108 BPF_STMT(BPF_RET+BPF_K, SECCOMP_RET_ALLOW), \
109 /* reload syscall number; all rules expect it in accumulator */ \
110 BPF_STMT(BPF_LD+BPF_W+BPF_ABS, \
111 offsetof(struct seccomp_data, nr))
113 /* Syscall filtering set for preauth. */
114 static const struct sock_filter preauth_insns[] = {
115 /* Ensure the syscall arch convention is as expected. */
116 BPF_STMT(BPF_LD+BPF_W+BPF_ABS,
117 offsetof(struct seccomp_data, arch)),
118 BPF_JUMP(BPF_JMP+BPF_JEQ+BPF_K, SECCOMP_AUDIT_ARCH, 1, 0),
119 BPF_STMT(BPF_RET+BPF_K, SECCOMP_FILTER_FAIL),
120 /* Load the syscall number for checking. */
121 BPF_STMT(BPF_LD+BPF_W+BPF_ABS,
122 offsetof(struct seccomp_data, nr)),
124 /* Syscalls to non-fatally deny */
126 SC_DENY(__NR_lstat, EACCES),
129 SC_DENY(__NR_lstat64, EACCES),
132 SC_DENY(__NR_fstat, EACCES),
135 SC_DENY(__NR_fstat64, EACCES),
138 SC_DENY(__NR_open, EACCES),
141 SC_DENY(__NR_openat, EACCES),
143 #ifdef __NR_newfstatat
144 SC_DENY(__NR_newfstatat, EACCES),
147 SC_DENY(__NR_stat, EACCES),
150 SC_DENY(__NR_stat64, EACCES),
153 /* Syscalls to permit */
157 #ifdef __NR_clock_gettime
158 SC_ALLOW(__NR_clock_gettime),
161 SC_ALLOW(__NR_close),
166 #ifdef __NR_exit_group
167 SC_ALLOW(__NR_exit_group),
170 SC_ALLOW(__NR_futex),
173 SC_ALLOW(__NR_geteuid),
175 #ifdef __NR_geteuid32
176 SC_ALLOW(__NR_geteuid32),
179 SC_ALLOW(__NR_getpgid),
182 SC_ALLOW(__NR_getpid),
184 #ifdef __NR_getrandom
185 SC_ALLOW(__NR_getrandom),
187 #ifdef __NR_gettimeofday
188 SC_ALLOW(__NR_gettimeofday),
191 SC_ALLOW(__NR_getuid),
194 SC_ALLOW(__NR_getuid32),
197 SC_ALLOW(__NR_madvise),
203 SC_ALLOW(__NR_mmap2),
206 SC_ALLOW(__NR_mremap),
209 SC_ALLOW(__NR_munmap),
211 #ifdef __NR_nanosleep
212 SC_ALLOW(__NR_nanosleep),
214 #ifdef __NR__newselect
215 SC_ALLOW(__NR__newselect),
221 SC_ALLOW(__NR_pselect6),
226 #ifdef __NR_rt_sigprocmask
227 SC_ALLOW(__NR_rt_sigprocmask),
230 SC_ALLOW(__NR_select),
233 SC_ALLOW(__NR_shutdown),
235 #ifdef __NR_sigprocmask
236 SC_ALLOW(__NR_sigprocmask),
242 SC_ALLOW(__NR_write),
244 #ifdef __NR_socketcall
245 SC_ALLOW_ARG(__NR_socketcall, 0, SYS_SHUTDOWN),
246 SC_DENY(__NR_socketcall, EACCES),
248 #if defined(__NR_ioctl) && defined(__s390__)
249 /* Allow ioctls for ICA crypto card on s390 */
250 SC_ALLOW_ARG(__NR_ioctl, 1, Z90STAT_STATUS_MASK),
251 SC_ALLOW_ARG(__NR_ioctl, 1, ICARSAMODEXPO),
252 SC_ALLOW_ARG(__NR_ioctl, 1, ICARSACRT),
254 #if defined(__x86_64__) && defined(__ILP32__) && defined(__X32_SYSCALL_BIT)
256 * On Linux x32, the clock_gettime VDSO falls back to the
257 * x86-64 syscall under some circumstances, e.g.
258 * https://bugs.debian.org/849923
260 SC_ALLOW(__NR_clock_gettime & ~__X32_SYSCALL_BIT),
264 BPF_STMT(BPF_RET+BPF_K, SECCOMP_FILTER_FAIL),
267 static const struct sock_fprog preauth_program = {
268 .len = (unsigned short)(sizeof(preauth_insns)/sizeof(preauth_insns[0])),
269 .filter = (struct sock_filter *)preauth_insns,
277 ssh_sandbox_init(struct monitor *monitor)
279 struct ssh_sandbox *box;
282 * Strictly, we don't need to maintain any state here but we need
283 * to return non-NULL to satisfy the API.
285 debug3("%s: preparing seccomp filter sandbox", __func__);
286 box = xcalloc(1, sizeof(*box));
292 #ifdef SANDBOX_SECCOMP_FILTER_DEBUG
293 extern struct monitor *pmonitor;
294 void mm_log_handler(LogLevel level, const char *msg, void *ctx);
297 ssh_sandbox_violation(int signum, siginfo_t *info, void *void_context)
301 snprintf(msg, sizeof(msg),
302 "%s: unexpected system call (arch:0x%x,syscall:%d @ %p)",
303 __func__, info->si_arch, info->si_syscall, info->si_call_addr);
304 mm_log_handler(SYSLOG_LEVEL_FATAL, msg, pmonitor);
309 ssh_sandbox_child_debugging(void)
311 struct sigaction act;
314 debug3("%s: installing SIGSYS handler", __func__);
315 memset(&act, 0, sizeof(act));
317 sigaddset(&mask, SIGSYS);
319 act.sa_sigaction = &ssh_sandbox_violation;
320 act.sa_flags = SA_SIGINFO;
321 if (sigaction(SIGSYS, &act, NULL) == -1)
322 fatal("%s: sigaction(SIGSYS): %s", __func__, strerror(errno));
323 if (sigprocmask(SIG_UNBLOCK, &mask, NULL) == -1)
324 fatal("%s: sigprocmask(SIGSYS): %s",
325 __func__, strerror(errno));
327 #endif /* SANDBOX_SECCOMP_FILTER_DEBUG */
330 ssh_sandbox_child(struct ssh_sandbox *box)
332 struct rlimit rl_zero;
335 /* Set rlimits for completeness if possible. */
336 rl_zero.rlim_cur = rl_zero.rlim_max = 0;
337 if (setrlimit(RLIMIT_FSIZE, &rl_zero) == -1)
338 fatal("%s: setrlimit(RLIMIT_FSIZE, { 0, 0 }): %s",
339 __func__, strerror(errno));
340 if (setrlimit(RLIMIT_NOFILE, &rl_zero) == -1)
341 fatal("%s: setrlimit(RLIMIT_NOFILE, { 0, 0 }): %s",
342 __func__, strerror(errno));
343 if (setrlimit(RLIMIT_NPROC, &rl_zero) == -1)
344 fatal("%s: setrlimit(RLIMIT_NPROC, { 0, 0 }): %s",
345 __func__, strerror(errno));
347 #ifdef SANDBOX_SECCOMP_FILTER_DEBUG
348 ssh_sandbox_child_debugging();
349 #endif /* SANDBOX_SECCOMP_FILTER_DEBUG */
351 debug3("%s: setting PR_SET_NO_NEW_PRIVS", __func__);
352 if (prctl(PR_SET_NO_NEW_PRIVS, 1, 0, 0, 0) == -1) {
353 debug("%s: prctl(PR_SET_NO_NEW_PRIVS): %s",
354 __func__, strerror(errno));
357 debug3("%s: attaching seccomp filter program", __func__);
358 if (prctl(PR_SET_SECCOMP, SECCOMP_MODE_FILTER, &preauth_program) == -1)
359 debug("%s: prctl(PR_SET_SECCOMP): %s",
360 __func__, strerror(errno));
362 fatal("%s: SECCOMP_MODE_FILTER activated but "
363 "PR_SET_NO_NEW_PRIVS failed", __func__);
367 ssh_sandbox_parent_finish(struct ssh_sandbox *box)
370 debug3("%s: finished", __func__);
374 ssh_sandbox_parent_preauth(struct ssh_sandbox *box, pid_t child_pid)
376 box->child_pid = child_pid;
379 #endif /* SANDBOX_SECCOMP_FILTER */