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>
64 #define MAP_ANON MAP_ANONYMOUS
68 #define min(a, b) (((a) < (b)) ? (a) : (b))
79 #define CRYPTO_SHA512_CTX SHA512_CTX
80 #define CRYPTO_SHA512_INIT(x) SHA512_Init(x)
81 #define CRYPTO_SHA512_FINAL(r, c) SHA512_Final(r, c)
82 #define HR(x, l) (SHA512_Update(&ctx, (char *)(x), (l)))
83 #define HD(x) (SHA512_Update(&ctx, (char *)&(x), sizeof (x)))
84 #define HF(x) (SHA512_Update(&ctx, (char *)&(x), sizeof (void*)))
85 #elif defined(HAVE_NETTLE)
86 #define CRYPTO_SHA512_CTX struct sha512_ctx
87 #define CRYPTO_SHA512_INIT(x) sha512_init(x)
88 #define CRYPTO_SHA512_FINAL(r, c) sha512_digest(c, SHA512_DIGEST_SIZE, r)
89 #define HR(x, l) (sha512_update(&ctx, (l), (uint8_t *)(x)))
90 #define HD(x) (sha512_update(&ctx, sizeof (x), (uint8_t *)&(x)))
91 #define HF(x) (sha512_update(&ctx, sizeof (void*), (uint8_t *)&(x)))
94 int getentropy(void *buf, size_t len);
96 #ifdef CAN_REFERENCE_MAIN
97 extern int main(int, char *argv[]);
99 static int gotdata(char *buf, size_t len);
100 #if defined(SYS_getrandom) && defined(__NR_getrandom)
101 static int getentropy_getrandom(void *buf, size_t len);
103 static int getentropy_urandom(void *buf, size_t len);
105 static int getentropy_sysctl(void *buf, size_t len);
107 static int getentropy_fallback(void *buf, size_t len);
110 getentropy(void *buf, size_t len)
119 #if defined(SYS_getrandom) && defined(__NR_getrandom)
121 * Try descriptor-less getrandom()
123 ret = getentropy_getrandom(buf, len);
131 * Try to get entropy with /dev/urandom
133 * This can fail if the process is inside a chroot or if file
134 * descriptors are exhausted.
136 ret = getentropy_urandom(buf, len);
142 * Try to use sysctl CTL_KERN, KERN_RANDOM, RANDOM_UUID.
143 * sysctl is a failsafe API, so it guarantees a result. This
144 * should work inside a chroot, or when file descriptors are
147 * However this can fail if the Linux kernel removes support
148 * for sysctl. Starting in 2007, there have been efforts to
149 * deprecate the sysctl API/ABI, and push callers towards use
150 * of the chroot-unavailable fd-using /proc mechanism --
151 * essentially the same problems as /dev/urandom.
153 * Numerous setbacks have been encountered in their deprecation
154 * schedule, so as of June 2014 the kernel ABI still exists on
155 * most Linux architectures. The sysctl() stub in libc is missing
156 * on some systems. There are also reports that some kernels
157 * spew messages to the console.
159 ret = getentropy_sysctl(buf, len);
162 #endif /* SYS__sysctl */
165 * Entropy collection via /dev/urandom and sysctl have failed.
167 * No other API exists for collecting entropy. See the large
168 * comment block above.
170 * We have very few options:
171 * - Even syslog_r is unsafe to call at this low level, so
172 * there is no way to alert the user or program.
173 * - Cannot call abort() because some systems have unsafe
175 * - Could raise(SIGKILL) resulting in silent program termination.
176 * - Return EIO, to hint that arc4random's stir function
177 * should raise(SIGKILL)
178 * - Do the best under the circumstances....
180 * This code path exists to bring light to the issue that Linux
181 * does not provide a failsafe API for entropy collection.
183 * We hope this demonstrates that Linux should either retain their
184 * sysctl ABI, or consider providing a new failsafe API which
185 * works in a chroot or when file descriptors are exhausted.
187 #undef FAIL_INSTEAD_OF_TRYING_FALLBACK
188 #ifdef FAIL_INSTEAD_OF_TRYING_FALLBACK
191 ret = getentropy_fallback(buf, len);
200 * Basic sanity checking; wish we could do better.
203 gotdata(char *buf, size_t len)
208 for (i = 0; i < len; ++i)
215 #if defined(SYS_getrandom) && defined(__NR_getrandom)
217 getentropy_getrandom(void *buf, size_t len)
219 int pre_errno = errno;
224 ret = syscall(SYS_getrandom, buf, len, 0);
225 } while (ret == -1 && errno == EINTR);
235 getentropy_urandom(void *buf, size_t len)
240 int save_errno = errno;
251 fd = open("/dev/urandom", flags, 0);
258 fcntl(fd, F_SETFD, fcntl(fd, F_GETFD) | FD_CLOEXEC);
261 /* Lightly verify that the device node looks sane */
262 if (fstat(fd, &st) == -1 || !S_ISCHR(st.st_mode)) {
266 if (ioctl(fd, RNDGETENTCNT, &cnt) == -1) {
270 for (i = 0; i < len; ) {
271 size_t wanted = len - i;
272 ssize_t ret = read(fd, (char*)buf + i, wanted);
275 if (errno == EAGAIN || errno == EINTR)
283 if (gotdata(buf, len) == 0) {
285 return 0; /* satisfied */
294 getentropy_sysctl(void *buf, size_t len)
296 static int mib[] = { CTL_KERN, KERN_RANDOM, RANDOM_UUID };
298 int save_errno = errno;
300 for (i = 0; i < len; ) {
301 size_t chunk = min(len - i, 16);
303 /* SYS__sysctl because some systems already removed sysctl() */
304 struct __sysctl_args args = {
307 .oldval = (char *)buf + i,
310 if (syscall(SYS__sysctl, &args) != 0)
314 if (gotdata(buf, len) == 0) {
316 return (0); /* satisfied */
322 #endif /* SYS__sysctl */
326 #ifdef CLOCK_MONOTONIC
329 #ifdef CLOCK_MONOTONIC_RAW
341 #ifdef CLOCK_PROCESS_CPUTIME_ID
342 CLOCK_PROCESS_CPUTIME_ID,
344 #ifdef CLOCK_THREAD_CPUTIME_ID
345 CLOCK_THREAD_CPUTIME_ID,
350 getentropy_fallback(void *buf, size_t len)
352 uint8_t results[SHA512_DIGEST_LENGTH];
353 int save_errno = errno, e, pgs = getpagesize(), faster = 0, repeat;
360 CRYPTO_SHA512_CTX ctx;
361 static pid_t lastpid;
367 if (lastpid == pid) {
375 for (i = 0; i < len; ) {
377 CRYPTO_SHA512_INIT(&ctx);
378 for (j = 0; j < repeat; j++) {
379 HX((e = gettimeofday(&tv, NULL)) == -1, tv);
381 cnt += (int)tv.tv_sec;
382 cnt += (int)tv.tv_usec;
385 for (ii = 0; ii < sizeof(cl)/sizeof(cl[0]); ii++)
386 HX(clock_gettime(cl[ii], &ts) == -1, ts);
388 HX((pid = getpid()) == -1, pid);
389 HX((pid = getsid(pid)) == -1, pid);
390 HX((pid = getppid()) == -1, pid);
391 HX((pid = getpgid(0)) == -1, pid);
392 HX((e = getpriority(0, 0)) == -1, e);
397 (void) nanosleep(&ts, NULL);
400 HX(sigpending(&sigset) == -1, sigset);
401 HX(sigprocmask(SIG_BLOCK, NULL, &sigset) == -1,
404 #ifdef CAN_REFERENCE_MAIN
405 HF(main); /* an addr in program */
407 HF(getentropy); /* an addr in this library */
408 HF(printf); /* an addr in libc */
410 HD(p); /* an addr on stack */
412 HD(p); /* the addr of errno */
415 struct sockaddr_storage ss;
416 struct statvfs stvfs;
423 * Prime-sized mappings encourage fragmentation;
424 * thus exposing some address entropy.
430 { 17, MAP_FAILED }, { 3, MAP_FAILED },
431 { 11, MAP_FAILED }, { 2, MAP_FAILED },
432 { 5, MAP_FAILED }, { 3, MAP_FAILED },
433 { 7, MAP_FAILED }, { 1, MAP_FAILED },
434 { 57, MAP_FAILED }, { 3, MAP_FAILED },
435 { 131, MAP_FAILED }, { 1, MAP_FAILED },
438 for (m = 0; m < sizeof mm/sizeof(mm[0]); m++) {
439 HX(mm[m].p = mmap(NULL,
441 PROT_READ|PROT_WRITE,
442 MAP_PRIVATE|MAP_ANON, -1,
444 if (mm[m].p != MAP_FAILED) {
447 /* Touch some memory... */
450 (mm[m].npg * pgs - 1);
452 cnt += (int)((long)(mm[m].p)
456 /* Check cnts and times... */
457 for (ii = 0; ii < sizeof(cl)/sizeof(cl[0]);
459 HX((e = clock_gettime(cl[ii],
462 cnt += (int)ts.tv_nsec;
465 HX((e = getrusage(RUSAGE_SELF,
468 cnt += (int)ru.ru_utime.tv_sec;
469 cnt += (int)ru.ru_utime.tv_usec;
473 for (m = 0; m < sizeof mm/sizeof(mm[0]); m++) {
474 if (mm[m].p != MAP_FAILED)
475 munmap(mm[m].p, mm[m].npg * pgs);
476 mm[m].p = MAP_FAILED;
479 HX(stat(".", &st) == -1, st);
480 HX(statvfs(".", &stvfs) == -1, stvfs);
481 HX(statfs(".", &stfs) == -1, stfs);
483 HX(stat("/", &st) == -1, st);
484 HX(statvfs("/", &stvfs) == -1, stvfs);
485 HX(statfs("/", &stfs) == -1, stfs);
487 HX((e = fstat(0, &st)) == -1, st);
489 if (S_ISREG(st.st_mode) ||
490 S_ISFIFO(st.st_mode) ||
491 S_ISSOCK(st.st_mode)) {
492 HX(fstatvfs(0, &stvfs) == -1,
494 HX(fstatfs(0, &stfs) == -1,
496 HX((off = lseek(0, (off_t)0,
497 SEEK_CUR)) < 0, off);
499 if (S_ISCHR(st.st_mode)) {
500 HX(tcgetattr(0, &tios) == -1,
502 } else if (S_ISSOCK(st.st_mode)) {
503 memset(&ss, 0, sizeof ss);
506 (void *)&ss, &ssl) == -1,
511 HX((e = getrusage(RUSAGE_CHILDREN,
514 cnt += (int)ru.ru_utime.tv_sec;
515 cnt += (int)ru.ru_utime.tv_usec;
518 /* Subsequent hashes absorb previous result */
522 HX((e = gettimeofday(&tv, NULL)) == -1, tv);
524 cnt += (int)tv.tv_sec;
525 cnt += (int)tv.tv_usec;
530 #ifdef HAVE_GETAUXVAL
532 /* Not as random as you think but we take what we are given */
533 p = (char *) getauxval(AT_RANDOM);
537 # ifdef AT_SYSINFO_EHDR
538 p = (char *) getauxval(AT_SYSINFO_EHDR);
543 p = (char *) getauxval(AT_BASE);
547 #endif /* HAVE_GETAUXVAL */
549 CRYPTO_SHA512_FINAL(results, &ctx);
550 memcpy((char*)buf + i, results, min(sizeof(results), len - i));
551 i += min(sizeof(results), len - i);
553 memset(results, 0, sizeof results);
554 if (gotdata(buf, len) == 0) {
556 return 0; /* satisfied */