1 /* $OpenBSD: getentropy_linux.c,v 1.42 2016/04/19 20:20:24 tj Exp $ */
4 * Copyright (c) 2014 Theo de Raadt <deraadt@openbsd.org>
5 * Copyright (c) 2014 Bob Beck <beck@obtuse.com>
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.
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.
19 * Emulation of getentropy(2) as documented at:
20 * http://man.openbsd.org/getentropy.2
23 #define _POSIX_C_SOURCE 199309L
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>
31 #include <linux/sysctl.h>
33 #include <sys/statvfs.h>
34 #include <sys/socket.h>
35 #include <sys/mount.h>
51 #include <openssl/sha.h>
54 #include <linux/types.h>
55 #include <linux/random.h>
62 #define min(a, b) (((a) < (b)) ? (a) : (b))
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*)))
76 int getentropy(void *buf, size_t len);
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);
82 static int getentropy_sysctl(void *buf, size_t len);
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);
90 getentropy(void *buf, size_t len)
100 * Try descriptor-less getrandom()
102 ret = getentropy_getrandom(buf, len);
105 if (errno != ENOSYS && errno != EAGAIN)
109 * Try to get entropy with /dev/urandom
111 * This can fail if the process is inside a chroot or if file
112 * descriptors are exhausted.
114 ret = getentropy_urandom(buf, len);
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
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.
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.
137 ret = getentropy_sysctl(buf, len);
140 #endif /* SYS__sysctl */
143 * Entropy collection via /dev/urandom and sysctl have failed.
145 * No other API exists for collecting entropy. See the large
146 * comment block above.
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
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....
158 * This code path exists to bring light to the issue that Linux
159 * does not provide a failsafe API for entropy collection.
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.
165 #undef FAIL_INSTEAD_OF_TRYING_FALLBACK
166 #ifdef FAIL_INSTEAD_OF_TRYING_FALLBACK
170 ret = getentropy_fallback(buf, len);
180 * Basic sanity checking; wish we could do better.
183 gotdata(char *buf, size_t len)
188 for (i = 0; i < len; ++i)
196 getentropy_getrandom(void *buf, size_t len)
198 int pre_errno = errno;
204 * Use GRND_NONBLOCK to avoid blocking before the
205 * entropy pool has been initialized
207 ret = syscall(SYS_getrandom, buf, len, GRND_NONBLOCK);
208 } while (ret == -1 && errno == EINTR);
210 if ((size_t)ret != len)
217 getentropy_urandom(void *buf, size_t len)
222 int save_errno = errno;
233 fd = open("/dev/urandom", flags, 0);
240 fcntl(fd, F_SETFD, fcntl(fd, F_GETFD) | FD_CLOEXEC);
243 /* Lightly verify that the device node looks sane */
244 if (fstat(fd, &st) == -1 || !S_ISCHR(st.st_mode)) {
248 if (ioctl(fd, RNDGETENTCNT, &cnt) == -1) {
252 for (i = 0; i < len; ) {
253 size_t wanted = len - i;
254 ssize_t ret = read(fd, (char *)buf + i, wanted);
257 if (errno == EAGAIN || errno == EINTR)
265 if (gotdata(buf, len) == 0) {
267 return (0); /* satisfied */
276 getentropy_sysctl(void *buf, size_t len)
278 static int mib[] = { CTL_KERN, KERN_RANDOM, RANDOM_UUID };
280 int save_errno = errno;
282 for (i = 0; i < len; ) {
283 size_t chunk = min(len - i, 16);
285 /* SYS__sysctl because some systems already removed sysctl() */
286 struct __sysctl_args args = {
289 .oldval = (char *)buf + i,
292 if (syscall(SYS__sysctl, &args) != 0)
296 if (gotdata(buf, len) == 0) {
298 return (0); /* satisfied */
304 #endif /* SYS__sysctl */
307 static const int cl[] = {
309 #ifdef CLOCK_MONOTONIC
312 #ifdef CLOCK_MONOTONIC_RAW
324 #ifdef CLOCK_PROCESS_CPUTIME_ID
325 CLOCK_PROCESS_CPUTIME_ID,
327 #ifdef CLOCK_THREAD_CPUTIME_ID
328 CLOCK_THREAD_CPUTIME_ID,
333 getentropy_phdr(struct dl_phdr_info *info, size_t size, void *data)
335 SHA512_CTX *ctx = data;
337 SHA512_Update(ctx, &info->dlpi_addr, sizeof (info->dlpi_addr));
342 getentropy_fallback(void *buf, size_t len)
344 uint8_t results[SHA512_DIGEST_LENGTH];
345 int save_errno = errno, e, pgs = getpagesize(), faster = 0, repeat;
353 static pid_t lastpid;
359 if (lastpid == pid) {
367 for (i = 0; i < len; ) {
370 for (j = 0; j < repeat; j++) {
371 HX((e = gettimeofday(&tv, NULL)) == -1, tv);
373 cnt += (int)tv.tv_sec;
374 cnt += (int)tv.tv_usec;
377 dl_iterate_phdr(getentropy_phdr, &ctx);
379 for (ii = 0; ii < sizeof(cl)/sizeof(cl[0]); ii++)
380 HX(clock_gettime(cl[ii], &ts) == -1, ts);
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);
391 (void) nanosleep(&ts, NULL);
394 HX(sigpending(&sigset) == -1, sigset);
395 HX(sigprocmask(SIG_BLOCK, NULL, &sigset) == -1,
398 HF(getentropy); /* an addr in this library */
399 HF(printf); /* an addr in libc */
401 HD(p); /* an addr on stack */
403 HD(p); /* the addr of errno */
406 struct sockaddr_storage ss;
407 struct statvfs stvfs;
414 * Prime-sized mappings encourage fragmentation;
415 * thus exposing some address entropy.
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 },
429 for (m = 0; m < sizeof mm/sizeof(mm[0]); m++) {
430 HX(mm[m].p = mmap(NULL,
432 PROT_READ|PROT_WRITE,
433 MAP_PRIVATE|MAP_ANON, -1,
435 if (mm[m].p != MAP_FAILED) {
438 /* Touch some memory... */
441 (mm[m].npg * pgs - 1);
443 cnt += (int)((long)(mm[m].p)
447 /* Check cnts and times... */
448 for (ii = 0; ii < sizeof(cl)/sizeof(cl[0]);
450 HX((e = clock_gettime(cl[ii],
453 cnt += (int)ts.tv_nsec;
456 HX((e = getrusage(RUSAGE_SELF,
459 cnt += (int)ru.ru_utime.tv_sec;
460 cnt += (int)ru.ru_utime.tv_usec;
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;
470 HX(stat(".", &st) == -1, st);
471 HX(statvfs(".", &stvfs) == -1, stvfs);
472 HX(statfs(".", &stfs) == -1, stfs);
474 HX(stat("/", &st) == -1, st);
475 HX(statvfs("/", &stvfs) == -1, stvfs);
476 HX(statfs("/", &stfs) == -1, stfs);
478 HX((e = fstat(0, &st)) == -1, st);
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,
485 HX(fstatfs(0, &stfs) == -1,
487 HX((off = lseek(0, (off_t)0,
488 SEEK_CUR)) < 0, off);
490 if (S_ISCHR(st.st_mode)) {
491 HX(tcgetattr(0, &tios) == -1,
493 } else if (S_ISSOCK(st.st_mode)) {
494 memset(&ss, 0, sizeof ss);
497 (void *)&ss, &ssl) == -1,
502 HX((e = getrusage(RUSAGE_CHILDREN,
505 cnt += (int)ru.ru_utime.tv_sec;
506 cnt += (int)ru.ru_utime.tv_usec;
509 /* Subsequent hashes absorb previous result */
513 HX((e = gettimeofday(&tv, NULL)) == -1, tv);
515 cnt += (int)tv.tv_sec;
516 cnt += (int)tv.tv_usec;
521 #ifdef HAVE_GETAUXVAL
523 /* Not as random as you think but we take what we are given */
524 p = (char *) getauxval(AT_RANDOM);
528 #ifdef AT_SYSINFO_EHDR
529 p = (char *) getauxval(AT_SYSINFO_EHDR);
534 p = (char *) getauxval(AT_BASE);
540 SHA512_Final(results, &ctx);
541 memcpy((char *)buf + i, results, min(sizeof(results), len - i));
542 i += min(sizeof(results), len - i);
544 memset(results, 0, sizeof results);
545 if (gotdata(buf, len) == 0) {
547 return (0); /* satisfied */
552 #endif /* HAVE_OPENSSL */