1 /* $OpenBSD: getentropy_linux.c,v 1.42 2016/04/19 20:20:24 tj 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://man.openbsd.org/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 SYS__sysctl
31 #include <linux/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/types.h>
55 #include <linux/random.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 static int getentropy_getrandom(void *buf, size_t len);
80 static int getentropy_urandom(void *buf, size_t len);
81 #ifdef SYS__sysctl
82 static int getentropy_sysctl(void *buf, size_t len);
83 #endif
84 #ifdef HAVE_OPENSSL
85 static int getentropy_fallback(void *buf, size_t len);
86 static int getentropy_phdr(struct dl_phdr_info *info, size_t size, void *data);
87 #endif
88
89 int
getentropy(void * buf,size_t len)90 getentropy(void *buf, size_t len)
91 {
92 int ret = -1;
93
94 if (len > 256) {
95 errno = EIO;
96 return (-1);
97 }
98
99 /*
100 * Try descriptor-less getrandom()
101 */
102 ret = getentropy_getrandom(buf, len);
103 if (ret != -1)
104 return (ret);
105 if (errno != ENOSYS && errno != EAGAIN)
106 return (-1);
107
108 /*
109 * Try to get entropy with /dev/urandom
110 *
111 * This can fail if the process is inside a chroot or if file
112 * descriptors are exhausted.
113 */
114 ret = getentropy_urandom(buf, len);
115 if (ret != -1)
116 return (ret);
117
118 #ifdef SYS__sysctl
119 /*
120 * Try to use sysctl CTL_KERN, KERN_RANDOM, RANDOM_UUID.
121 * sysctl is a failsafe API, so it guarantees a result. This
122 * should work inside a chroot, or when file descriptors are
123 * exhausted.
124 *
125 * However this can fail if the Linux kernel removes support
126 * for sysctl. Starting in 2007, there have been efforts to
127 * deprecate the sysctl API/ABI, and push callers towards use
128 * of the chroot-unavailable fd-using /proc mechanism --
129 * essentially the same problems as /dev/urandom.
130 *
131 * Numerous setbacks have been encountered in their deprecation
132 * schedule, so as of June 2014 the kernel ABI still exists on
133 * most Linux architectures. The sysctl() stub in libc is missing
134 * on some systems. There are also reports that some kernels
135 * spew messages to the console.
136 */
137 ret = getentropy_sysctl(buf, len);
138 if (ret != -1)
139 return (ret);
140 #endif /* SYS__sysctl */
141
142 /*
143 * Entropy collection via /dev/urandom and sysctl have failed.
144 *
145 * No other API exists for collecting entropy. See the large
146 * comment block above.
147 *
148 * We have very few options:
149 * - Even syslog_r is unsafe to call at this low level, so
150 * there is no way to alert the user or program.
151 * - Cannot call abort() because some systems have unsafe
152 * corefiles.
153 * - Could raise(SIGKILL) resulting in silent program termination.
154 * - Return EIO, to hint that arc4random's stir function
155 * should raise(SIGKILL)
156 * - Do the best under the circumstances....
157 *
158 * This code path exists to bring light to the issue that Linux
159 * does not provide a failsafe API for entropy collection.
160 *
161 * We hope this demonstrates that Linux should either retain their
162 * sysctl ABI, or consider providing a new failsafe API which
163 * works in a chroot or when file descriptors are exhausted.
164 */
165 #undef FAIL_INSTEAD_OF_TRYING_FALLBACK
166 #ifdef FAIL_INSTEAD_OF_TRYING_FALLBACK
167 raise(SIGKILL);
168 #endif
169 #ifdef HAVE_OPENSSL
170 ret = getentropy_fallback(buf, len);
171 if (ret != -1)
172 return (ret);
173 #endif
174
175 errno = EIO;
176 return (ret);
177 }
178
179 /*
180 * Basic sanity checking; wish we could do better.
181 */
182 static int
gotdata(char * buf,size_t len)183 gotdata(char *buf, size_t len)
184 {
185 char any_set = 0;
186 size_t i;
187
188 for (i = 0; i < len; ++i)
189 any_set |= buf[i];
190 if (any_set == 0)
191 return (-1);
192 return (0);
193 }
194
195 static int
getentropy_getrandom(void * buf,size_t len)196 getentropy_getrandom(void *buf, size_t len)
197 {
198 int pre_errno = errno;
199 int ret;
200 if (len > 256)
201 return (-1);
202 do {
203 /*
204 * Use GRND_NONBLOCK to avoid blocking before the
205 * entropy pool has been initialized
206 */
207 ret = syscall(SYS_getrandom, buf, len, GRND_NONBLOCK);
208 } while (ret == -1 && errno == EINTR);
209
210 if ((size_t)ret != len)
211 return (-1);
212 errno = pre_errno;
213 return (0);
214 }
215
216 static int
getentropy_urandom(void * buf,size_t len)217 getentropy_urandom(void *buf, size_t len)
218 {
219 struct stat st;
220 size_t i;
221 int fd, cnt, flags;
222 int save_errno = errno;
223
224 start:
225
226 flags = O_RDONLY;
227 #ifdef O_NOFOLLOW
228 flags |= O_NOFOLLOW;
229 #endif
230 #ifdef O_CLOEXEC
231 flags |= O_CLOEXEC;
232 #endif
233 fd = open("/dev/urandom", flags, 0);
234 if (fd == -1) {
235 if (errno == EINTR)
236 goto start;
237 goto nodevrandom;
238 }
239 #ifndef O_CLOEXEC
240 fcntl(fd, F_SETFD, fcntl(fd, F_GETFD) | FD_CLOEXEC);
241 #endif
242
243 /* Lightly verify that the device node looks sane */
244 if (fstat(fd, &st) == -1 || !S_ISCHR(st.st_mode)) {
245 close(fd);
246 goto nodevrandom;
247 }
248 if (ioctl(fd, RNDGETENTCNT, &cnt) == -1) {
249 close(fd);
250 goto nodevrandom;
251 }
252 for (i = 0; i < len; ) {
253 size_t wanted = len - i;
254 ssize_t ret = read(fd, (char *)buf + i, wanted);
255
256 if (ret == -1) {
257 if (errno == EAGAIN || errno == EINTR)
258 continue;
259 close(fd);
260 goto nodevrandom;
261 }
262 i += ret;
263 }
264 close(fd);
265 if (gotdata(buf, len) == 0) {
266 errno = save_errno;
267 return (0); /* satisfied */
268 }
269 nodevrandom:
270 errno = EIO;
271 return (-1);
272 }
273
274 #ifdef SYS__sysctl
275 static int
getentropy_sysctl(void * buf,size_t len)276 getentropy_sysctl(void *buf, size_t len)
277 {
278 static int mib[] = { CTL_KERN, KERN_RANDOM, RANDOM_UUID };
279 size_t i;
280 int save_errno = errno;
281
282 for (i = 0; i < len; ) {
283 size_t chunk = min(len - i, 16);
284
285 /* SYS__sysctl because some systems already removed sysctl() */
286 struct __sysctl_args args = {
287 .name = mib,
288 .nlen = 3,
289 .oldval = (char *)buf + i,
290 .oldlenp = &chunk,
291 };
292 if (syscall(SYS__sysctl, &args) != 0)
293 goto sysctlfailed;
294 i += chunk;
295 }
296 if (gotdata(buf, len) == 0) {
297 errno = save_errno;
298 return (0); /* satisfied */
299 }
300 sysctlfailed:
301 errno = EIO;
302 return (-1);
303 }
304 #endif /* SYS__sysctl */
305
306 #ifdef HAVE_OPENSSL
307 static const int cl[] = {
308 CLOCK_REALTIME,
309 #ifdef CLOCK_MONOTONIC
310 CLOCK_MONOTONIC,
311 #endif
312 #ifdef CLOCK_MONOTONIC_RAW
313 CLOCK_MONOTONIC_RAW,
314 #endif
315 #ifdef CLOCK_TAI
316 CLOCK_TAI,
317 #endif
318 #ifdef CLOCK_VIRTUAL
319 CLOCK_VIRTUAL,
320 #endif
321 #ifdef CLOCK_UPTIME
322 CLOCK_UPTIME,
323 #endif
324 #ifdef CLOCK_PROCESS_CPUTIME_ID
325 CLOCK_PROCESS_CPUTIME_ID,
326 #endif
327 #ifdef CLOCK_THREAD_CPUTIME_ID
328 CLOCK_THREAD_CPUTIME_ID,
329 #endif
330 };
331
332 static int
getentropy_phdr(struct dl_phdr_info * info,size_t size,void * data)333 getentropy_phdr(struct dl_phdr_info *info, size_t size, void *data)
334 {
335 SHA512_CTX *ctx = data;
336
337 SHA512_Update(ctx, &info->dlpi_addr, sizeof (info->dlpi_addr));
338 return (0);
339 }
340
341 static int
getentropy_fallback(void * buf,size_t len)342 getentropy_fallback(void *buf, size_t len)
343 {
344 uint8_t results[SHA512_DIGEST_LENGTH];
345 int save_errno = errno, e, pgs = getpagesize(), faster = 0, repeat;
346 static int cnt;
347 struct timespec ts;
348 struct timeval tv;
349 struct rusage ru;
350 sigset_t sigset;
351 struct stat st;
352 SHA512_CTX ctx;
353 static pid_t lastpid;
354 pid_t pid;
355 size_t i, ii, m;
356 char *p;
357
358 pid = getpid();
359 if (lastpid == pid) {
360 faster = 1;
361 repeat = 2;
362 } else {
363 faster = 0;
364 lastpid = pid;
365 repeat = REPEAT;
366 }
367 for (i = 0; i < len; ) {
368 int j;
369 SHA512_Init(&ctx);
370 for (j = 0; j < repeat; j++) {
371 HX((e = gettimeofday(&tv, NULL)) == -1, tv);
372 if (e != -1) {
373 cnt += (int)tv.tv_sec;
374 cnt += (int)tv.tv_usec;
375 }
376
377 dl_iterate_phdr(getentropy_phdr, &ctx);
378
379 for (ii = 0; ii < sizeof(cl)/sizeof(cl[0]); ii++)
380 HX(clock_gettime(cl[ii], &ts) == -1, ts);
381
382 HX((pid = getpid()) == -1, pid);
383 HX((pid = getsid(pid)) == -1, pid);
384 HX((pid = getppid()) == -1, pid);
385 HX((pid = getpgid(0)) == -1, pid);
386 HX((e = getpriority(0, 0)) == -1, e);
387
388 if (!faster) {
389 ts.tv_sec = 0;
390 ts.tv_nsec = 1;
391 (void) nanosleep(&ts, NULL);
392 }
393
394 HX(sigpending(&sigset) == -1, sigset);
395 HX(sigprocmask(SIG_BLOCK, NULL, &sigset) == -1,
396 sigset);
397
398 HF(getentropy); /* an addr in this library */
399 HF(printf); /* an addr in libc */
400 p = (char *)&p;
401 HD(p); /* an addr on stack */
402 p = (char *)&errno;
403 HD(p); /* the addr of errno */
404
405 if (i == 0) {
406 struct sockaddr_storage ss;
407 struct statvfs stvfs;
408 struct termios tios;
409 struct statfs stfs;
410 socklen_t ssl;
411 off_t off;
412
413 /*
414 * Prime-sized mappings encourage fragmentation;
415 * thus exposing some address entropy.
416 */
417 struct mm {
418 size_t npg;
419 void *p;
420 } mm[] = {
421 { 17, MAP_FAILED }, { 3, MAP_FAILED },
422 { 11, MAP_FAILED }, { 2, MAP_FAILED },
423 { 5, MAP_FAILED }, { 3, MAP_FAILED },
424 { 7, MAP_FAILED }, { 1, MAP_FAILED },
425 { 57, MAP_FAILED }, { 3, MAP_FAILED },
426 { 131, MAP_FAILED }, { 1, MAP_FAILED },
427 };
428
429 for (m = 0; m < sizeof mm/sizeof(mm[0]); m++) {
430 HX(mm[m].p = mmap(NULL,
431 mm[m].npg * pgs,
432 PROT_READ|PROT_WRITE,
433 MAP_PRIVATE|MAP_ANON, -1,
434 (off_t)0), mm[m].p);
435 if (mm[m].p != MAP_FAILED) {
436 size_t mo;
437
438 /* Touch some memory... */
439 p = mm[m].p;
440 mo = cnt %
441 (mm[m].npg * pgs - 1);
442 p[mo] = 1;
443 cnt += (int)((long)(mm[m].p)
444 / pgs);
445 }
446
447 /* Check cnts and times... */
448 for (ii = 0; ii < sizeof(cl)/sizeof(cl[0]);
449 ii++) {
450 HX((e = clock_gettime(cl[ii],
451 &ts)) == -1, ts);
452 if (e != -1)
453 cnt += (int)ts.tv_nsec;
454 }
455
456 HX((e = getrusage(RUSAGE_SELF,
457 &ru)) == -1, ru);
458 if (e != -1) {
459 cnt += (int)ru.ru_utime.tv_sec;
460 cnt += (int)ru.ru_utime.tv_usec;
461 }
462 }
463
464 for (m = 0; m < sizeof mm/sizeof(mm[0]); m++) {
465 if (mm[m].p != MAP_FAILED)
466 munmap(mm[m].p, mm[m].npg * pgs);
467 mm[m].p = MAP_FAILED;
468 }
469
470 HX(stat(".", &st) == -1, st);
471 HX(statvfs(".", &stvfs) == -1, stvfs);
472 HX(statfs(".", &stfs) == -1, stfs);
473
474 HX(stat("/", &st) == -1, st);
475 HX(statvfs("/", &stvfs) == -1, stvfs);
476 HX(statfs("/", &stfs) == -1, stfs);
477
478 HX((e = fstat(0, &st)) == -1, st);
479 if (e == -1) {
480 if (S_ISREG(st.st_mode) ||
481 S_ISFIFO(st.st_mode) ||
482 S_ISSOCK(st.st_mode)) {
483 HX(fstatvfs(0, &stvfs) == -1,
484 stvfs);
485 HX(fstatfs(0, &stfs) == -1,
486 stfs);
487 HX((off = lseek(0, (off_t)0,
488 SEEK_CUR)) < 0, off);
489 }
490 if (S_ISCHR(st.st_mode)) {
491 HX(tcgetattr(0, &tios) == -1,
492 tios);
493 } else if (S_ISSOCK(st.st_mode)) {
494 memset(&ss, 0, sizeof ss);
495 ssl = sizeof(ss);
496 HX(getpeername(0,
497 (void *)&ss, &ssl) == -1,
498 ss);
499 }
500 }
501
502 HX((e = getrusage(RUSAGE_CHILDREN,
503 &ru)) == -1, ru);
504 if (e != -1) {
505 cnt += (int)ru.ru_utime.tv_sec;
506 cnt += (int)ru.ru_utime.tv_usec;
507 }
508 } else {
509 /* Subsequent hashes absorb previous result */
510 HD(results);
511 }
512
513 HX((e = gettimeofday(&tv, NULL)) == -1, tv);
514 if (e != -1) {
515 cnt += (int)tv.tv_sec;
516 cnt += (int)tv.tv_usec;
517 }
518
519 HD(cnt);
520 }
521 #ifdef HAVE_GETAUXVAL
522 #ifdef AT_RANDOM
523 /* Not as random as you think but we take what we are given */
524 p = (char *) getauxval(AT_RANDOM);
525 if (p)
526 HR(p, 16);
527 #endif
528 #ifdef AT_SYSINFO_EHDR
529 p = (char *) getauxval(AT_SYSINFO_EHDR);
530 if (p)
531 HR(p, pgs);
532 #endif
533 #ifdef AT_BASE
534 p = (char *) getauxval(AT_BASE);
535 if (p)
536 HD(p);
537 #endif
538 #endif
539
540 SHA512_Final(results, &ctx);
541 memcpy((char *)buf + i, results, min(sizeof(results), len - i));
542 i += min(sizeof(results), len - i);
543 }
544 memset(results, 0, sizeof results);
545 if (gotdata(buf, len) == 0) {
546 errno = save_errno;
547 return (0); /* satisfied */
548 }
549 errno = EIO;
550 return (-1);
551 }
552 #endif /* HAVE_OPENSSL */
553