1 /* $OpenBSD: getentropy_linux.c,v 1.20 2014/07/12 15:43:49 beck 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.
22 #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>
30 #ifdef HAVE_SYS_SYSCTL_H
31 #include <sys/sysctl.h>
33 #include <sys/statvfs.h>
34 #include <sys/socket.h>
35 #include <sys/mount.h>
51 #include <openssl/sha.h>
52 #elif defined(HAVE_NETTLE)
53 #include <nettle/sha.h>
56 #include <linux/types.h>
57 #include <linux/random.h>
58 #include <linux/sysctl.h>
65 #define min(a, b) (((a) < (b)) ? (a) : (b))
76 #define CRYPTO_SHA512_CTX SHA512_CTX
77 #define CRYPTO_SHA512_INIT(x) SHA512_Init(x)
78 #define CRYPTO_SHA512_FINAL(r, c) SHA512_Final(r, c)
79 #define HR(x, l) (SHA512_Update(&ctx, (char *)(x), (l)))
80 #define HD(x) (SHA512_Update(&ctx, (char *)&(x), sizeof (x)))
81 #define HF(x) (SHA512_Update(&ctx, (char *)&(x), sizeof (void*)))
82 #elif defined(HAVE_NETTLE)
83 #define CRYPTO_SHA512_CTX struct sha512_ctx
84 #define CRYPTO_SHA512_INIT(x) sha512_init(x)
85 #define CRYPTO_SHA512_FINAL(r, c) sha512_digest(c, SHA512_DIGEST_SIZE, r)
86 #define HR(x, l) (sha512_update(&ctx, (l), (uint8_t *)(x)))
87 #define HD(x) (sha512_update(&ctx, sizeof (x), (uint8_t *)&(x)))
88 #define HF(x) (sha512_update(&ctx, sizeof (void*), (uint8_t *)&(x)))
91 int getentropy(void *buf, size_t len);
93 #ifdef CAN_REFERENCE_MAIN
94 extern int main(int, char *argv[]);
96 static int gotdata(char *buf, size_t len);
98 static int getentropy_getrandom(void *buf, size_t len);
100 static int getentropy_urandom(void *buf, size_t len);
102 static int getentropy_sysctl(void *buf, size_t len);
104 static int getentropy_fallback(void *buf, size_t len);
107 getentropy(void *buf, size_t len)
118 * Try descriptor-less getrandom()
120 ret = getentropy_getrandom(buf, len);
128 * Try to get entropy with /dev/urandom
130 * This can fail if the process is inside a chroot or if file
131 * descriptors are exhausted.
133 ret = getentropy_urandom(buf, len);
139 * Try to use sysctl CTL_KERN, KERN_RANDOM, RANDOM_UUID.
140 * sysctl is a failsafe API, so it guarantees a result. This
141 * should work inside a chroot, or when file descriptors are
144 * However this can fail if the Linux kernel removes support
145 * for sysctl. Starting in 2007, there have been efforts to
146 * deprecate the sysctl API/ABI, and push callers towards use
147 * of the chroot-unavailable fd-using /proc mechanism --
148 * essentially the same problems as /dev/urandom.
150 * Numerous setbacks have been encountered in their deprecation
151 * schedule, so as of June 2014 the kernel ABI still exists on
152 * most Linux architectures. The sysctl() stub in libc is missing
153 * on some systems. There are also reports that some kernels
154 * spew messages to the console.
156 ret = getentropy_sysctl(buf, len);
159 #endif /* SYS__sysctl */
162 * Entropy collection via /dev/urandom and sysctl have failed.
164 * No other API exists for collecting entropy. See the large
165 * comment block above.
167 * We have very few options:
168 * - Even syslog_r is unsafe to call at this low level, so
169 * there is no way to alert the user or program.
170 * - Cannot call abort() because some systems have unsafe
172 * - Could raise(SIGKILL) resulting in silent program termination.
173 * - Return EIO, to hint that arc4random's stir function
174 * should raise(SIGKILL)
175 * - Do the best under the circumstances....
177 * This code path exists to bring light to the issue that Linux
178 * does not provide a failsafe API for entropy collection.
180 * We hope this demonstrates that Linux should either retain their
181 * sysctl ABI, or consider providing a new failsafe API which
182 * works in a chroot or when file descriptors are exhausted.
184 #undef FAIL_INSTEAD_OF_TRYING_FALLBACK
185 #ifdef FAIL_INSTEAD_OF_TRYING_FALLBACK
188 ret = getentropy_fallback(buf, len);
197 * Basic sanity checking; wish we could do better.
200 gotdata(char *buf, size_t len)
205 for (i = 0; i < len; ++i)
214 getentropy_getrandom(void *buf, size_t len)
216 int pre_errno = errno;
221 ret = syscall(SYS_getrandom, buf, len, 0);
222 } while (ret == -1 && errno == EINTR);
232 getentropy_urandom(void *buf, size_t len)
237 int save_errno = errno;
248 fd = open("/dev/urandom", flags, 0);
255 fcntl(fd, F_SETFD, fcntl(fd, F_GETFD) | FD_CLOEXEC);
258 /* Lightly verify that the device node looks sane */
259 if (fstat(fd, &st) == -1 || !S_ISCHR(st.st_mode)) {
263 if (ioctl(fd, RNDGETENTCNT, &cnt) == -1) {
267 for (i = 0; i < len; ) {
268 size_t wanted = len - i;
269 ssize_t ret = read(fd, (char*)buf + i, wanted);
272 if (errno == EAGAIN || errno == EINTR)
280 if (gotdata(buf, len) == 0) {
282 return 0; /* satisfied */
291 getentropy_sysctl(void *buf, size_t len)
293 static int mib[] = { CTL_KERN, KERN_RANDOM, RANDOM_UUID };
295 int save_errno = errno;
297 for (i = 0; i < len; ) {
298 size_t chunk = min(len - i, 16);
300 /* SYS__sysctl because some systems already removed sysctl() */
301 struct __sysctl_args args = {
304 .oldval = (char *)buf + i,
307 if (syscall(SYS__sysctl, &args) != 0)
311 if (gotdata(buf, len) == 0) {
313 return (0); /* satisfied */
319 #endif /* SYS__sysctl */
323 #ifdef CLOCK_MONOTONIC
326 #ifdef CLOCK_MONOTONIC_RAW
338 #ifdef CLOCK_PROCESS_CPUTIME_ID
339 CLOCK_PROCESS_CPUTIME_ID,
341 #ifdef CLOCK_THREAD_CPUTIME_ID
342 CLOCK_THREAD_CPUTIME_ID,
347 getentropy_fallback(void *buf, size_t len)
349 uint8_t results[SHA512_DIGEST_LENGTH];
350 int save_errno = errno, e, pgs = getpagesize(), faster = 0, repeat;
357 CRYPTO_SHA512_CTX ctx;
358 static pid_t lastpid;
364 if (lastpid == pid) {
372 for (i = 0; i < len; ) {
374 CRYPTO_SHA512_INIT(&ctx);
375 for (j = 0; j < repeat; j++) {
376 HX((e = gettimeofday(&tv, NULL)) == -1, tv);
378 cnt += (int)tv.tv_sec;
379 cnt += (int)tv.tv_usec;
382 for (ii = 0; ii < sizeof(cl)/sizeof(cl[0]); ii++)
383 HX(clock_gettime(cl[ii], &ts) == -1, ts);
385 HX((pid = getpid()) == -1, pid);
386 HX((pid = getsid(pid)) == -1, pid);
387 HX((pid = getppid()) == -1, pid);
388 HX((pid = getpgid(0)) == -1, pid);
389 HX((e = getpriority(0, 0)) == -1, e);
394 (void) nanosleep(&ts, NULL);
397 HX(sigpending(&sigset) == -1, sigset);
398 HX(sigprocmask(SIG_BLOCK, NULL, &sigset) == -1,
401 #ifdef CAN_REFERENCE_MAIN
402 HF(main); /* an addr in program */
404 HF(getentropy); /* an addr in this library */
405 HF(printf); /* an addr in libc */
407 HD(p); /* an addr on stack */
409 HD(p); /* the addr of errno */
412 struct sockaddr_storage ss;
413 struct statvfs stvfs;
420 * Prime-sized mappings encourage fragmentation;
421 * thus exposing some address entropy.
427 { 17, MAP_FAILED }, { 3, MAP_FAILED },
428 { 11, MAP_FAILED }, { 2, MAP_FAILED },
429 { 5, MAP_FAILED }, { 3, MAP_FAILED },
430 { 7, MAP_FAILED }, { 1, MAP_FAILED },
431 { 57, MAP_FAILED }, { 3, MAP_FAILED },
432 { 131, MAP_FAILED }, { 1, MAP_FAILED },
435 for (m = 0; m < sizeof mm/sizeof(mm[0]); m++) {
436 HX(mm[m].p = mmap(NULL,
438 PROT_READ|PROT_WRITE,
439 MAP_PRIVATE|MAP_ANON, -1,
441 if (mm[m].p != MAP_FAILED) {
444 /* Touch some memory... */
447 (mm[m].npg * pgs - 1);
449 cnt += (int)((long)(mm[m].p)
453 /* Check cnts and times... */
454 for (ii = 0; ii < sizeof(cl)/sizeof(cl[0]);
456 HX((e = clock_gettime(cl[ii],
459 cnt += (int)ts.tv_nsec;
462 HX((e = getrusage(RUSAGE_SELF,
465 cnt += (int)ru.ru_utime.tv_sec;
466 cnt += (int)ru.ru_utime.tv_usec;
470 for (m = 0; m < sizeof mm/sizeof(mm[0]); m++) {
471 if (mm[m].p != MAP_FAILED)
472 munmap(mm[m].p, mm[m].npg * pgs);
473 mm[m].p = MAP_FAILED;
476 HX(stat(".", &st) == -1, st);
477 HX(statvfs(".", &stvfs) == -1, stvfs);
478 HX(statfs(".", &stfs) == -1, stfs);
480 HX(stat("/", &st) == -1, st);
481 HX(statvfs("/", &stvfs) == -1, stvfs);
482 HX(statfs("/", &stfs) == -1, stfs);
484 HX((e = fstat(0, &st)) == -1, st);
486 if (S_ISREG(st.st_mode) ||
487 S_ISFIFO(st.st_mode) ||
488 S_ISSOCK(st.st_mode)) {
489 HX(fstatvfs(0, &stvfs) == -1,
491 HX(fstatfs(0, &stfs) == -1,
493 HX((off = lseek(0, (off_t)0,
494 SEEK_CUR)) < 0, off);
496 if (S_ISCHR(st.st_mode)) {
497 HX(tcgetattr(0, &tios) == -1,
499 } else if (S_ISSOCK(st.st_mode)) {
500 memset(&ss, 0, sizeof ss);
503 (void *)&ss, &ssl) == -1,
508 HX((e = getrusage(RUSAGE_CHILDREN,
511 cnt += (int)ru.ru_utime.tv_sec;
512 cnt += (int)ru.ru_utime.tv_usec;
515 /* Subsequent hashes absorb previous result */
519 HX((e = gettimeofday(&tv, NULL)) == -1, tv);
521 cnt += (int)tv.tv_sec;
522 cnt += (int)tv.tv_usec;
527 #ifdef HAVE_GETAUXVAL
529 /* Not as random as you think but we take what we are given */
530 p = (char *) getauxval(AT_RANDOM);
534 # ifdef AT_SYSINFO_EHDR
535 p = (char *) getauxval(AT_SYSINFO_EHDR);
540 p = (char *) getauxval(AT_BASE);
544 #endif /* HAVE_GETAUXVAL */
546 CRYPTO_SHA512_FINAL(results, &ctx);
547 memcpy((char*)buf + i, results, min(sizeof(results), len - i));
548 i += min(sizeof(results), len - i);
550 memset(results, 0, sizeof results);
551 if (gotdata(buf, len) == 0) {
553 return 0; /* satisfied */