1 /*
2  * Copyright (c) 2021 Omar Polo <op@omarpolo.com>
3  *
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.
7  *
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.
15  */
16 
17 #include "gmid.h"
18 
19 #if defined(__FreeBSD__)
20 
21 #include <sys/capsicum.h>
22 
23 void
24 sandbox_server_process(void)
25 {
26 	if (cap_enter() == -1)
27 		fatal("cap_enter");
28 }
29 
30 void
31 sandbox_executor_process(void)
32 {
33 	/* We cannot capsicum the executor process because it needs
34 	 * to fork(2)+execve(2) cgi scripts */
35 	return;
36 }
37 
38 void
39 sandbox_logger_process(void)
40 {
41 	if (cap_enter() == -1)
42 		fatal("cap_enter");
43 }
44 
45 #elif defined(__linux__)
46 
47 #include <sys/prctl.h>
48 #include <sys/syscall.h>
49 #include <sys/syscall.h>
50 #include <sys/types.h>
51 
52 #include <linux/audit.h>
53 #include <linux/filter.h>
54 #include <linux/seccomp.h>
55 
56 #include <errno.h>
57 #include <fcntl.h>
58 #include <stddef.h>
59 #include <stdio.h>
60 #include <string.h>
61 
62 /* uncomment to enable debugging.  ONLY FOR DEVELOPMENT */
63 /* #define SC_DEBUG */
64 
65 #ifdef SC_DEBUG
66 # define SC_FAIL SECCOMP_RET_TRAP
67 #else
68 # define SC_FAIL SECCOMP_RET_KILL
69 #endif
70 
71 #if (BYTE_ORDER == LITTLE_ENDIAN)
72 # define SC_ARG_LO	0
73 # define SC_ARG_HI	sizeof(uint32_t)
74 #elif (BYTE_ORDER == BIG_ENDIAN)
75 # define SC_ARG_LO	sizeof(uint32_t)
76 # define SC_ARG_HI	0
77 #else
78 # error "Uknown endian"
79 #endif
80 
81 /* make the filter more readable */
82 #define SC_ALLOW(nr)						\
83 	BPF_JUMP(BPF_JMP | BPF_JEQ | BPF_K, __NR_##nr, 0, 1),	\
84 	BPF_STMT(BPF_RET | BPF_K, SECCOMP_RET_ALLOW)
85 
86 /*
87  * SC_ALLOW_ARG and the SECCOMP_AUDIT_ARCH below are courtesy of
88  * https://roy.marples.name/git/dhcpcd/blob/HEAD:/src/privsep-linux.c
89  */
90 #define SC_ALLOW_ARG(_nr, _arg, _val)						\
91 	BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, (_nr), 0, 6),			\
92 	BPF_STMT(BPF_LD + BPF_W + BPF_ABS,					\
93 	    offsetof(struct seccomp_data, args[(_arg)]) + SC_ARG_LO),		\
94 	BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K,					\
95 	    ((_val) & 0xffffffff), 0, 3),					\
96 	BPF_STMT(BPF_LD + BPF_W + BPF_ABS,					\
97 	    offsetof(struct seccomp_data, args[(_arg)]) + SC_ARG_HI),		\
98 	BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K,					\
99 	    (((uint32_t)((uint64_t)(_val) >> 32)) & 0xffffffff), 0, 1),		\
100 	BPF_STMT(BPF_RET + BPF_K, SECCOMP_RET_ALLOW),				\
101 	BPF_STMT(BPF_LD + BPF_W + BPF_ABS,					\
102 	    offsetof(struct seccomp_data, nr))
103 
104 /*
105  * I personally find this quite nutty.  Why can a system header not
106  * define a default for this?
107  */
108 #if defined(__i386__)
109 #  define SECCOMP_AUDIT_ARCH AUDIT_ARCH_I386
110 #elif defined(__x86_64__)
111 #  define SECCOMP_AUDIT_ARCH AUDIT_ARCH_X86_64
112 #elif defined(__arc__)
113 #  if defined(__A7__)
114 #    if (BYTE_ORDER == LITTLE_ENDIAN)
115 #      define SECCOMP_AUDIT_ARCH AUDIT_ARCH_ARCOMPACT
116 #    else
117 #      define SECCOMP_AUDIT_ARCH AUDIT_ARCH_ARCOMPACTBE
118 #    endif
119 #  elif defined(__HS__)
120 #    if (BYTE_ORDER == LITTLE_ENDIAN)
121 #      define SECCOMP_AUDIT_ARCH AUDIT_ARCH_ARCV2
122 #    else
123 #      define SECCOMP_AUDIT_ARCH AUDIT_ARCH_ARCV2BE
124 #    endif
125 #  else
126 #    error "Platform does not support seccomp filter yet"
127 #  endif
128 #elif defined(__arm__)
129 #  ifndef EM_ARM
130 #    define EM_ARM 40
131 #  endif
132 #  if (BYTE_ORDER == LITTLE_ENDIAN)
133 #    define SECCOMP_AUDIT_ARCH AUDIT_ARCH_ARM
134 #  else
135 #    define SECCOMP_AUDIT_ARCH AUDIT_ARCH_ARMEB
136 #  endif
137 #elif defined(__aarch64__)
138 #  define SECCOMP_AUDIT_ARCH AUDIT_ARCH_AARCH64
139 #elif defined(__alpha__)
140 #  define SECCOMP_AUDIT_ARCH AUDIT_ARCH_ALPHA
141 #elif defined(__hppa__)
142 #  if defined(__LP64__)
143 #    define SECCOMP_AUDIT_ARCH AUDIT_ARCH_PARISC64
144 #  else
145 #    define SECCOMP_AUDIT_ARCH AUDIT_ARCH_PARISC
146 #  endif
147 #elif defined(__ia64__)
148 #  define SECCOMP_AUDIT_ARCH AUDIT_ARCH_IA64
149 #elif defined(__microblaze__)
150 #  define SECCOMP_AUDIT_ARCH AUDIT_ARCH_MICROBLAZE
151 #elif defined(__m68k__)
152 #  define SECCOMP_AUDIT_ARCH AUDIT_ARCH_M68K
153 #elif defined(__mips__)
154 #  if defined(__MIPSEL__)
155 #    if defined(__LP64__)
156 #      define SECCOMP_AUDIT_ARCH AUDIT_ARCH_MIPSEL64
157 #    else
158 #      define SECCOMP_AUDIT_ARCH AUDIT_ARCH_MIPSEL
159 #    endif
160 #  elif defined(__LP64__)
161 #    define SECCOMP_AUDIT_ARCH AUDIT_ARCH_MIPS64
162 #  else
163 #    define SECCOMP_AUDIT_ARCH AUDIT_ARCH_MIPS
164 #  endif
165 #elif defined(__nds32__)
166 #  if (BYTE_ORDER == LITTLE_ENDIAN)
167 #    define SECCOMP_AUDIT_ARCH AUDIT_ARCH_NDS32
168 #else
169 #    define SECCOMP_AUDIT_ARCH AUDIT_ARCH_NDS32BE
170 #endif
171 #elif defined(__nios2__)
172 #  define SECCOMP_AUDIT_ARCH AUDIT_ARCH_NIOS2
173 #elif defined(__or1k__)
174 #  define SECCOMP_AUDIT_ARCH AUDIT_ARCH_OPENRISC
175 #elif defined(__powerpc64__)
176 #  define SECCOMP_AUDIT_ARCH AUDIT_ARCH_PPC64
177 #elif defined(__powerpc__)
178 #  define SECCOMP_AUDIT_ARCH AUDIT_ARCH_PPC
179 #elif defined(__riscv)
180 #  if defined(__LP64__)
181 #    define SECCOMP_AUDIT_ARCH AUDIT_ARCH_RISCV64
182 #  else
183 #    define SECCOMP_AUDIT_ARCH AUDIT_ARCH_RISCV32
184 #  endif
185 #elif defined(__s390x__)
186 #  define SECCOMP_AUDIT_ARCH AUDIT_ARCH_S390X
187 #elif defined(__s390__)
188 #  define SECCOMP_AUDIT_ARCH AUDIT_ARCH_S390
189 #elif defined(__sh__)
190 #  if defined(__LP64__)
191 #    if (BYTE_ORDER == LITTLE_ENDIAN)
192 #      define SECCOMP_AUDIT_ARCH AUDIT_ARCH_SHEL64
193 #    else
194 #      define SECCOMP_AUDIT_ARCH AUDIT_ARCH_SH64
195 #    endif
196 #  else
197 #    if (BYTE_ORDER == LITTLE_ENDIAN)
198 #      define SECCOMP_AUDIT_ARCH AUDIT_ARCH_SHEL
199 #    else
200 #      define SECCOMP_AUDIT_ARCH AUDIT_ARCH_SH
201 #    endif
202 #  endif
203 #elif defined(__sparc__)
204 #  if defined(__arch64__)
205 #    define SECCOMP_AUDIT_ARCH AUDIT_ARCH_SPARC64
206 #  else
207 #    define SECCOMP_AUDIT_ARCH AUDIT_ARCH_SPARC
208 #  endif
209 #elif defined(__xtensa__)
210 #  define SECCOMP_AUDIT_ARCH AUDIT_ARCH_XTENSA
211 #else
212 #  error "Platform does not support seccomp filter yet"
213 #endif
214 
215 static struct sock_filter filter[] = {
216 	/* load the *current* architecture */
217 	BPF_STMT(BPF_LD | BPF_W | BPF_ABS,
218 	    (offsetof(struct seccomp_data, arch))),
219 	/* ensure it's the same that we've been compiled on */
220 	BPF_JUMP(BPF_JMP | BPF_JEQ | BPF_K,
221 	    SECCOMP_AUDIT_ARCH, 1, 0),
222 	/* if not, kill the program */
223 	BPF_STMT(BPF_RET | BPF_K, SC_FAIL),
224 
225 	/* load the syscall number */
226 	BPF_STMT(BPF_LD | BPF_W | BPF_ABS,
227 	    (offsetof(struct seccomp_data, nr))),
228 
229 #ifdef __NR_accept
230 	SC_ALLOW(accept),
231 #endif
232 #ifdef __NR_accept4
233 	SC_ALLOW(accept4),
234 #endif
235 #ifdef __NR_brk
236 	SC_ALLOW(brk),
237 #endif
238 #ifdef __NR_clock_gettime
239 	SC_ALLOW(clock_gettime),
240 #endif
241 #if defined(__x86_64__) && defined(__ILP32__) && defined(__X32_SYSCALL_BIT)
242 	SECCOMP_ALLOW(__NR_clock_gettime & ~__X32_SYSCALL_BIT),
243 #endif
244 #ifdef __NR_clock_gettime64
245 	SC_ALLOW(clock_gettime64),
246 #endif
247 #ifdef __NR_close
248 	SC_ALLOW(close),
249 #endif
250 #ifdef __NR_epoll_ctl
251 	SC_ALLOW(epoll_ctl),
252 #endif
253 #ifdef __NR_epoll_pwait
254 	SC_ALLOW(epoll_pwait),
255 #endif
256 #ifdef __NR_epoll_wait
257 	SC_ALLOW(epoll_wait),
258 #endif
259 #ifdef __NR_exit
260 	SC_ALLOW(exit),
261 #endif
262 #ifdef __NR_exit_group
263 	SC_ALLOW(exit_group),
264 #endif
265 #ifdef __NR_fcntl
266 	SC_ALLOW(fcntl),
267 #endif
268 #ifdef __NR_fcntl64
269 	SC_ALLOW(fcntl64),
270 #endif
271 #ifdef __NR_fstat
272 	SC_ALLOW(fstat),
273 #endif
274 #ifdef __NR_getdents64
275 	SC_ALLOW(getdents64),
276 #endif
277 #ifdef __NR_getpid
278 	SC_ALLOW(getpid),
279 #endif
280 #ifdef __NR_getrandom
281 	SC_ALLOW(getrandom),
282 #endif
283 #ifdef __NR_gettimeofday
284 	SC_ALLOW(gettimeofday),
285 #endif
286 #ifdef __NR_ioctl
287 	/* allow ioctl only on fd 1, glibc doing stuff? */
288         SC_ALLOW_ARG(__NR_ioctl, 0, 1),
289 #endif
290 #ifdef __NR_lseek
291 	SC_ALLOW(lseek),
292 #endif
293 #ifdef __NR_madvise
294 	SC_ALLOW(madvise),
295 #endif
296 #ifdef __NR_mmap
297 	SC_ALLOW(mmap),
298 #endif
299 #ifdef __NR_mmap2
300 	SC_ALLOW(mmap2),
301 #endif
302 #ifdef __NR_munmap
303 	SC_ALLOW(munmap),
304 #endif
305 #ifdef __NR_newfstatat
306 	SC_ALLOW(newfstatat),
307 #endif
308 #ifdef __NR_oldfstat
309 	SC_ALLOW(oldfstat),
310 #endif
311 #ifdef __NR_openat
312 	SC_ALLOW(openat),
313 #endif
314 #ifdef __NR_prlimit64
315 	SC_ALLOW(prlimit64),
316 #endif
317 #ifdef __NR_read
318 	SC_ALLOW(read),
319 #endif
320 #ifdef __NR_recvmsg
321 	SC_ALLOW(recvmsg),
322 #endif
323 #ifdef __NR_redav
324 	SC_ALLOW(redav),
325 #endif
326 #ifdef __NR_rt_sigaction
327 	SC_ALLOW(rt_sigaction),
328 #endif
329 #ifdef __NR_rt_sigreturn
330 	SC_ALLOW(rt_sigreturn),
331 #endif
332 #ifdef __NR_sendmsg
333 	SC_ALLOW(sendmsg),
334 #endif
335 #ifdef __NR_statx
336 	SC_ALLOW(statx),
337 #endif
338 #ifdef __NR_write
339 	SC_ALLOW(write),
340 #endif
341 #ifdef __NR_writev
342 	SC_ALLOW(writev),
343 #endif
344 
345 	/* disallow enything else */
346 	BPF_STMT(BPF_RET | BPF_K, SC_FAIL),
347 };
348 
349 #ifdef SC_DEBUG
350 
351 #include <signal.h>
352 #include <unistd.h>
353 
354 static void
355 sandbox_seccomp_violation(int signum, siginfo_t *info, void *ctx)
356 {
357 	(void)signum;
358 	(void)ctx;
359 
360 	fprintf(stderr, "%s: unexpected system call (arch:0x%x,syscall:%d @ %p)\n",
361 	    __func__, info->si_arch, info->si_syscall, info->si_call_addr);
362 	_exit(1);
363 }
364 
365 static void
366 sandbox_seccomp_catch_sigsys(void)
367 {
368 	struct sigaction act;
369 	sigset_t mask;
370 
371 	memset(&act, 0, sizeof(act));
372 	sigemptyset(&mask);
373 	sigaddset(&mask, SIGSYS);
374 
375 	act.sa_sigaction = &sandbox_seccomp_violation;
376 	act.sa_flags = SA_SIGINFO;
377 	if (sigaction(SIGSYS, &act, NULL) == -1)
378 		fatal("%s: sigaction(SIGSYS): %s",
379 		    __func__, strerror(errno));
380 
381 	if (sigprocmask(SIG_UNBLOCK, &mask, NULL) == -1)
382 		fatal("%s: sigprocmask(SIGSYS): %s\n",
383 		    __func__, strerror(errno));
384 }
385 #endif	/* SC_DEBUG */
386 
387 void
388 sandbox_server_process(void)
389 {
390 	struct sock_fprog prog = {
391 		.len = (unsigned short) (sizeof(filter) / sizeof(filter[0])),
392 		.filter = filter,
393 	};
394 
395 #ifdef SC_DEBUG
396 	sandbox_seccomp_catch_sigsys();
397 #endif
398 
399 	if (prctl(PR_SET_NO_NEW_PRIVS, 1, 0, 0, 0) == -1)
400 		fatal("%s: prctl(PR_SET_NO_NEW_PRIVS): %s",
401 		    __func__, strerror(errno));
402 
403 	if (prctl(PR_SET_SECCOMP, SECCOMP_MODE_FILTER, &prog) == -1)
404 		fatal("%s: prctl(PR_SET_SECCOMP): %s\n",
405 		    __func__, strerror(errno));
406 }
407 
408 void
409 sandbox_executor_process(void)
410 {
411 	/* We cannot use seccomp for the executor process because we
412 	 * don't know what the child will do.  Also, our filter will
413 	 * be inherited so the child cannot set its own seccomp
414 	 * policy. */
415 	return;
416 }
417 
418 void
419 sandbox_logger_process(void)
420 {
421 	/* To be honest, here we could use a seccomp policy to only
422 	 * allow writev(2) and memory allocations. */
423 	return;
424 }
425 
426 #elif defined(__OpenBSD__)
427 
428 #include <unistd.h>
429 
430 void
431 sandbox_server_process(void)
432 {
433 	struct vhost *h;
434 
435 	for (h = hosts; h->domain != NULL; ++h) {
436 		if (unveil(h->dir, "r") == -1)
437 			fatal("unveil %s for domain %s", h->dir, h->domain);
438 	}
439 
440 	if (pledge("stdio recvfd rpath inet", NULL) == -1)
441 		fatal("pledge");
442 }
443 
444 void
445 sandbox_executor_process(void)
446 {
447 	struct vhost	*vhost;
448 
449 	for (vhost = hosts; vhost->domain != NULL; ++vhost) {
450 		/* r so we can chdir into the correct directory */
451 		if (unveil(vhost->dir, "rx") == -1)
452 			err(1, "unveil %s for domain %s",
453 			    vhost->dir, vhost->domain);
454 	}
455 
456 	/* rpath to chdir into the correct directory */
457 	if (pledge("stdio rpath sendfd proc exec", NULL))
458 		err(1, "pledge");
459 }
460 
461 void
462 sandbox_logger_process(void)
463 {
464 	if (pledge("stdio", NULL) == -1)
465 		err(1, "pledge");
466 }
467 
468 #else
469 
470 #warning "No sandbox method known for this OS"
471 
472 void
473 sandbox_server_process(void)
474 {
475 	return;
476 }
477 
478 void
479 sandbox_executor_process(void)
480 {
481 	log_notice(NULL, "no sandbox method known for this OS");
482 }
483 
484 void
485 sandbox_logger_process(void)
486 {
487 	return;
488 }
489 
490 #endif