• Home
  • Line#
  • Scopes#
  • Navigate#
  • Raw
  • Download
1 /*	$OpenBSD: getentropy_linux.c,v 1.28 2014/07/20 03:24:10 deraadt Exp $	*/
2 
3 /*
4  * Copyright (c) 2014 Theo de Raadt <deraadt@openbsd.org>
5  * Copyright (c) 2014 Bob Beck <beck@obtuse.com>
6  *
7  * Permission to use, copy, modify, and distribute this software for any
8  * purpose with or without fee is hereby granted, provided that the above
9  * copyright notice and this permission notice appear in all copies.
10  *
11  * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
12  * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
13  * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
14  * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
15  * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
16  * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
17  * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
18  *
19  * Emulation of getentropy(2) as documented at:
20  * http://www.openbsd.org/cgi-bin/man.cgi/OpenBSD-current/man2/getentropy.2
21  */
22 
23 #define	_POSIX_C_SOURCE	199309L
24 #define	_GNU_SOURCE	1
25 #include <sys/types.h>
26 #include <sys/param.h>
27 #include <sys/ioctl.h>
28 #include <sys/resource.h>
29 #include <sys/syscall.h>
30 #ifdef HAVE_SYS_SYSCTL_H
31 #include <sys/sysctl.h>
32 #endif
33 #include <sys/statvfs.h>
34 #include <sys/socket.h>
35 #include <sys/mount.h>
36 #include <sys/mman.h>
37 #include <sys/stat.h>
38 #include <sys/time.h>
39 #include <stdlib.h>
40 #include <stdint.h>
41 #include <stdio.h>
42 #include <link.h>
43 #include <termios.h>
44 #include <fcntl.h>
45 #include <signal.h>
46 #include <string.h>
47 #include <errno.h>
48 #include <unistd.h>
49 #include <time.h>
50 #ifdef HAVE_OPENSSL
51 #include <openssl/sha.h>
52 #endif
53 
54 #include <linux/random.h>
55 #include <linux/sysctl.h>
56 #ifdef HAVE_GETAUXVAL
57 #include <sys/auxv.h>
58 #endif
59 #include <sys/vfs.h>
60 
61 #define REPEAT 5
62 #define min(a, b) (((a) < (b)) ? (a) : (b))
63 
64 #define HX(a, b) \
65 	do { \
66 		if ((a)) \
67 			HD(errno); \
68 		else \
69 			HD(b); \
70 	} while (0)
71 
72 #define HR(x, l) (SHA512_Update(&ctx, (char *)(x), (l)))
73 #define HD(x)	 (SHA512_Update(&ctx, (char *)&(x), sizeof (x)))
74 #define HF(x)    (SHA512_Update(&ctx, (char *)&(x), sizeof (void*)))
75 
76 int	getentropy(void *buf, size_t len);
77 
78 static int gotdata(char *buf, size_t len);
79 #ifdef SYS__getrandom
80 static int getentropy_getrandom(void *buf, size_t len);
81 #endif
82 static int getentropy_urandom(void *buf, size_t len);
83 #ifdef SYS__sysctl
84 static int getentropy_sysctl(void *buf, size_t len);
85 #endif
86 #ifdef HAVE_OPENSSL
87 static int getentropy_fallback(void *buf, size_t len);
88 static int getentropy_phdr(struct dl_phdr_info *info, size_t size, void *data);
89 #endif
90 
91 int
getentropy(void * buf,size_t len)92 getentropy(void *buf, size_t len)
93 {
94 	int ret = -1;
95 
96 	if (len > 256) {
97 		errno = EIO;
98 		return -1;
99 	}
100 
101 #ifdef SYS__getrandom
102 	/*
103 	 * Try descriptor-less getrandom()
104 	 */
105 	ret = getentropy_getrandom(buf, len);
106 	if (ret != -1)
107 		return (ret);
108 #endif
109 
110 	/*
111 	 * Try to get entropy with /dev/urandom
112 	 *
113 	 * This can fail if the process is inside a chroot or if file
114 	 * descriptors are exhausted.
115 	 */
116 	ret = getentropy_urandom(buf, len);
117 	if (ret != -1)
118 		return (ret);
119 
120 #ifdef SYS__sysctl
121 	/*
122 	 * Try to use sysctl CTL_KERN, KERN_RANDOM, RANDOM_UUID.
123 	 * sysctl is a failsafe API, so it guarantees a result.  This
124 	 * should work inside a chroot, or when file descriptors are
125 	 * exhuasted.
126 	 *
127 	 * However this can fail if the Linux kernel removes support
128 	 * for sysctl.  Starting in 2007, there have been efforts to
129 	 * deprecate the sysctl API/ABI, and push callers towards use
130 	 * of the chroot-unavailable fd-using /proc mechanism --
131 	 * essentially the same problems as /dev/urandom.
132 	 *
133 	 * Numerous setbacks have been encountered in their deprecation
134 	 * schedule, so as of June 2014 the kernel ABI still exists on
135 	 * most Linux architectures. The sysctl() stub in libc is missing
136 	 * on some systems.  There are also reports that some kernels
137 	 * spew messages to the console.
138 	 */
139 	ret = getentropy_sysctl(buf, len);
140 	if (ret != -1)
141 		return (ret);
142 #endif /* SYS__sysctl */
143 
144 	/*
145 	 * Entropy collection via /dev/urandom and sysctl have failed.
146 	 *
147 	 * No other API exists for collecting entropy.  See the large
148 	 * comment block above.
149 	 *
150 	 * We have very few options:
151 	 *     - Even syslog_r is unsafe to call at this low level, so
152 	 *	 there is no way to alert the user or program.
153 	 *     - Cannot call abort() because some systems have unsafe
154 	 *	 corefiles.
155 	 *     - Could raise(SIGKILL) resulting in silent program termination.
156 	 *     - Return EIO, to hint that arc4random's stir function
157 	 *       should raise(SIGKILL)
158 	 *     - Do the best under the circumstances....
159 	 *
160 	 * This code path exists to bring light to the issue that Linux
161 	 * does not provide a failsafe API for entropy collection.
162 	 *
163 	 * We hope this demonstrates that Linux should either retain their
164 	 * sysctl ABI, or consider providing a new failsafe API which
165 	 * works in a chroot or when file descriptors are exhausted.
166 	 */
167 #undef FAIL_INSTEAD_OF_TRYING_FALLBACK
168 #ifdef FAIL_INSTEAD_OF_TRYING_FALLBACK
169 	raise(SIGKILL);
170 #endif
171 #ifdef HAVE_OPENSSL
172 	ret = getentropy_fallback(buf, len);
173 	if (ret != -1)
174 		return (ret);
175 #endif
176 
177 	errno = EIO;
178 	return (ret);
179 }
180 
181 /*
182  * Basic sanity checking; wish we could do better.
183  */
184 static int
gotdata(char * buf,size_t len)185 gotdata(char *buf, size_t len)
186 {
187 	char	any_set = 0;
188 	size_t	i;
189 
190 	for (i = 0; i < len; ++i)
191 		any_set |= buf[i];
192 	if (any_set == 0)
193 		return -1;
194 	return 0;
195 }
196 
197 #ifdef SYS__getrandom
198 static int
getentropy_getrandom(void * buf,size_t len)199 getentropy_getrandom(void *buf, size_t len)
200 {
201 #if 0
202 
203 /* Hand-definitions until the API becomes commonplace */
204 #ifndef SYS__getrandom
205 #ifdef __LP64__
206 #define SYS__getrandom 317
207 #else
208 #define SYS__getrandom 354
209 #endif
210 #endif
211 	struct __getrandom_args args = {
212 		.buf = buf;
213 		.len = len;
214 		.flags = 0;
215 	};
216 
217 	if (len > 256)
218 		return (-1);
219 	ret = syscall(SYS__getrandom, &args);
220 	if (ret == len)
221 		return (0);
222 #endif
223 	return -1;
224 }
225 #endif
226 
227 static int
getentropy_urandom(void * buf,size_t len)228 getentropy_urandom(void *buf, size_t len)
229 {
230 	struct stat st;
231 	size_t i;
232 	int fd, cnt, flags;
233 	int save_errno = errno;
234 
235 start:
236 
237 	flags = O_RDONLY;
238 #ifdef O_NOFOLLOW
239 	flags |= O_NOFOLLOW;
240 #endif
241 #ifdef O_CLOEXEC
242 	flags |= O_CLOEXEC;
243 #endif
244 	fd = open("/dev/urandom", flags, 0);
245 	if (fd == -1) {
246 		if (errno == EINTR)
247 			goto start;
248 		goto nodevrandom;
249 	}
250 #ifndef O_CLOEXEC
251 	fcntl(fd, F_SETFD, fcntl(fd, F_GETFD) | FD_CLOEXEC);
252 #endif
253 
254 	/* Lightly verify that the device node looks sane */
255 	if (fstat(fd, &st) == -1 || !S_ISCHR(st.st_mode)) {
256 		close(fd);
257 		goto nodevrandom;
258 	}
259 	if (ioctl(fd, RNDGETENTCNT, &cnt) == -1) {
260 		close(fd);
261 		goto nodevrandom;
262 	}
263 	for (i = 0; i < len; ) {
264 		size_t wanted = len - i;
265 		ssize_t ret = read(fd, (char *)buf + i, wanted);
266 
267 		if (ret == -1) {
268 			if (errno == EAGAIN || errno == EINTR)
269 				continue;
270 			close(fd);
271 			goto nodevrandom;
272 		}
273 		i += ret;
274 	}
275 	close(fd);
276 	if (gotdata(buf, len) == 0) {
277 		errno = save_errno;
278 		return 0;		/* satisfied */
279 	}
280 nodevrandom:
281 	errno = EIO;
282 	return -1;
283 }
284 
285 #ifdef SYS__sysctl
286 static int
getentropy_sysctl(void * buf,size_t len)287 getentropy_sysctl(void *buf, size_t len)
288 {
289 	static int mib[] = { CTL_KERN, KERN_RANDOM, RANDOM_UUID };
290 	size_t i;
291 	int save_errno = errno;
292 
293 	for (i = 0; i < len; ) {
294 		size_t chunk = min(len - i, 16);
295 
296 		/* SYS__sysctl because some systems already removed sysctl() */
297 		struct __sysctl_args args = {
298 			.name = mib,
299 			.nlen = 3,
300 			.oldval = (char*) buf + i,
301 			.oldlenp = &chunk,
302 		};
303 		if (syscall(SYS__sysctl, &args) != 0)
304 			goto sysctlfailed;
305 		i += chunk;
306 	}
307 	if (gotdata(buf, len) == 0) {
308 		errno = save_errno;
309 		return (0);			/* satisfied */
310 	}
311 sysctlfailed:
312 	errno = EIO;
313 	return -1;
314 }
315 #endif /* SYS__sysctl */
316 
317 #ifdef HAVE_OPENSSL
318 
319 static int cl[] = {
320 	CLOCK_REALTIME,
321 #ifdef CLOCK_MONOTONIC
322 	CLOCK_MONOTONIC,
323 #endif
324 #ifdef CLOCK_MONOTONIC_RAW
325 	CLOCK_MONOTONIC_RAW,
326 #endif
327 #ifdef CLOCK_TAI
328 	CLOCK_TAI,
329 #endif
330 #ifdef CLOCK_VIRTUAL
331 	CLOCK_VIRTUAL,
332 #endif
333 #ifdef CLOCK_UPTIME
334 	CLOCK_UPTIME,
335 #endif
336 #ifdef CLOCK_PROCESS_CPUTIME_ID
337 	CLOCK_PROCESS_CPUTIME_ID,
338 #endif
339 #ifdef CLOCK_THREAD_CPUTIME_ID
340 	CLOCK_THREAD_CPUTIME_ID,
341 #endif
342 };
343 
344 static int
getentropy_phdr(struct dl_phdr_info * info,size_t size,void * data)345 getentropy_phdr(struct dl_phdr_info *info, size_t size, void *data)
346 {
347 	SHA512_CTX *ctx = data;
348 
349 	SHA512_Update(ctx, &info->dlpi_addr, sizeof (info->dlpi_addr));
350 	return 0;
351 }
352 
353 static int
getentropy_fallback(void * buf,size_t len)354 getentropy_fallback(void *buf, size_t len)
355 {
356 	uint8_t results[SHA512_DIGEST_LENGTH];
357 	int save_errno = errno, e, pgs = getpagesize(), faster = 0, repeat;
358 	static int cnt;
359 	struct timespec ts;
360 	struct timeval tv;
361 	struct rusage ru;
362 	sigset_t sigset;
363 	struct stat st;
364 	SHA512_CTX ctx;
365 	static pid_t lastpid;
366 	pid_t pid;
367 	size_t i, ii, m;
368 	char *p;
369 
370 	pid = getpid();
371 	if (lastpid == pid) {
372 		faster = 1;
373 		repeat = 2;
374 	} else {
375 		faster = 0;
376 		lastpid = pid;
377 		repeat = REPEAT;
378 	}
379 	for (i = 0; i < len; ) {
380 		int j;
381 		SHA512_Init(&ctx);
382 		for (j = 0; j < repeat; j++) {
383 			HX((e = gettimeofday(&tv, NULL)) == -1, tv);
384 			if (e != -1) {
385 				cnt += (int)tv.tv_sec;
386 				cnt += (int)tv.tv_usec;
387 			}
388 
389 			dl_iterate_phdr(getentropy_phdr, &ctx);
390 
391 			for (ii = 0; ii < sizeof(cl)/sizeof(cl[0]); ii++)
392 				HX(clock_gettime(cl[ii], &ts) == -1, ts);
393 
394 			HX((pid = getpid()) == -1, pid);
395 			HX((pid = getsid(pid)) == -1, pid);
396 			HX((pid = getppid()) == -1, pid);
397 			HX((pid = getpgid(0)) == -1, pid);
398 			HX((e = getpriority(0, 0)) == -1, e);
399 
400 			if (!faster) {
401 				ts.tv_sec = 0;
402 				ts.tv_nsec = 1;
403 				(void) nanosleep(&ts, NULL);
404 			}
405 
406 			HX(sigpending(&sigset) == -1, sigset);
407 			HX(sigprocmask(SIG_BLOCK, NULL, &sigset) == -1,
408 			    sigset);
409 
410 			HF(getentropy);	/* an addr in this library */
411 			HF(printf);		/* an addr in libc */
412 			p = (char *)&p;
413 			HD(p);		/* an addr on stack */
414 			p = (char *)&errno;
415 			HD(p);		/* the addr of errno */
416 
417 			if (i == 0) {
418 				struct sockaddr_storage ss;
419 				struct statvfs stvfs;
420 				struct termios tios;
421 				struct statfs stfs;
422 				socklen_t ssl;
423 				off_t off;
424 
425 				/*
426 				 * Prime-sized mappings encourage fragmentation;
427 				 * thus exposing some address entropy.
428 				 */
429 				struct mm {
430 					size_t	npg;
431 					void	*p;
432 				} mm[] =	 {
433 					{ 17, MAP_FAILED }, { 3, MAP_FAILED },
434 					{ 11, MAP_FAILED }, { 2, MAP_FAILED },
435 					{ 5, MAP_FAILED }, { 3, MAP_FAILED },
436 					{ 7, MAP_FAILED }, { 1, MAP_FAILED },
437 					{ 57, MAP_FAILED }, { 3, MAP_FAILED },
438 					{ 131, MAP_FAILED }, { 1, MAP_FAILED },
439 				};
440 
441 				for (m = 0; m < sizeof mm/sizeof(mm[0]); m++) {
442 					HX(mm[m].p = mmap(NULL,
443 					    mm[m].npg * pgs,
444 					    PROT_READ|PROT_WRITE,
445 					    MAP_PRIVATE|MAP_ANON, -1,
446 					    (off_t)0), mm[m].p);
447 					if (mm[m].p != MAP_FAILED) {
448 						size_t mo;
449 
450 						/* Touch some memory... */
451 						p = mm[m].p;
452 						mo = cnt %
453 						    (mm[m].npg * pgs - 1);
454 						p[mo] = 1;
455 						cnt += (int)((long)(mm[m].p)
456 						    / pgs);
457 					}
458 
459 					/* Check cnts and times... */
460 					for (ii = 0; ii < sizeof(cl)/sizeof(cl[0]);
461 					    ii++) {
462 						HX((e = clock_gettime(cl[ii],
463 						    &ts)) == -1, ts);
464 						if (e != -1)
465 							cnt += (int)ts.tv_nsec;
466 					}
467 
468 					HX((e = getrusage(RUSAGE_SELF,
469 					    &ru)) == -1, ru);
470 					if (e != -1) {
471 						cnt += (int)ru.ru_utime.tv_sec;
472 						cnt += (int)ru.ru_utime.tv_usec;
473 					}
474 				}
475 
476 				for (m = 0; m < sizeof mm/sizeof(mm[0]); m++) {
477 					if (mm[m].p != MAP_FAILED)
478 						munmap(mm[m].p, mm[m].npg * pgs);
479 					mm[m].p = MAP_FAILED;
480 				}
481 
482 				HX(stat(".", &st) == -1, st);
483 				HX(statvfs(".", &stvfs) == -1, stvfs);
484 				HX(statfs(".", &stfs) == -1, stfs);
485 
486 				HX(stat("/", &st) == -1, st);
487 				HX(statvfs("/", &stvfs) == -1, stvfs);
488 				HX(statfs("/", &stfs) == -1, stfs);
489 
490 				HX((e = fstat(0, &st)) == -1, st);
491 				if (e == -1) {
492 					if (S_ISREG(st.st_mode) ||
493 					    S_ISFIFO(st.st_mode) ||
494 					    S_ISSOCK(st.st_mode)) {
495 						HX(fstatvfs(0, &stvfs) == -1,
496 						    stvfs);
497 						HX(fstatfs(0, &stfs) == -1,
498 						    stfs);
499 						HX((off = lseek(0, (off_t)0,
500 						    SEEK_CUR)) < 0, off);
501 					}
502 					if (S_ISCHR(st.st_mode)) {
503 						HX(tcgetattr(0, &tios) == -1,
504 						    tios);
505 					} else if (S_ISSOCK(st.st_mode)) {
506 						memset(&ss, 0, sizeof ss);
507 						ssl = sizeof(ss);
508 						HX(getpeername(0,
509 						    (void *)&ss, &ssl) == -1,
510 						    ss);
511 					}
512 				}
513 
514 				HX((e = getrusage(RUSAGE_CHILDREN,
515 				    &ru)) == -1, ru);
516 				if (e != -1) {
517 					cnt += (int)ru.ru_utime.tv_sec;
518 					cnt += (int)ru.ru_utime.tv_usec;
519 				}
520 			} else {
521 				/* Subsequent hashes absorb previous result */
522 				HD(results);
523 			}
524 
525 			HX((e = gettimeofday(&tv, NULL)) == -1, tv);
526 			if (e != -1) {
527 				cnt += (int)tv.tv_sec;
528 				cnt += (int)tv.tv_usec;
529 			}
530 
531 			HD(cnt);
532 		}
533 #ifdef HAVE_GETAUXVAL
534 #ifdef AT_RANDOM
535 		/* Not as random as you think but we take what we are given */
536 		p = (char *) getauxval(AT_RANDOM);
537 		if (p)
538 			HR(p, 16);
539 #endif
540 #ifdef AT_SYSINFO_EHDR
541 		p = (char *) getauxval(AT_SYSINFO_EHDR);
542 		if (p)
543 			HR(p, pgs);
544 #endif
545 #ifdef AT_BASE
546 		p = (char *) getauxval(AT_BASE);
547 		if (p)
548 			HD(p);
549 #endif
550 #endif
551 
552 		SHA512_Final(results, &ctx);
553 		memcpy((char *)buf + i, results, min(sizeof(results), len - i));
554 		i += min(sizeof(results), len - i);
555 	}
556 	memset(results, 0, sizeof results);
557 	if (gotdata(buf, len) == 0) {
558 		errno = save_errno;
559 		return 0;		/* satisfied */
560 	}
561 	errno = EIO;
562 	return -1;
563 }
564 
565 #endif /* HAVE_OPENSSL */
566