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>
49 #include <openssl/sha.h>
51 #include <linux/types.h>
52 #include <linux/random.h>
53 #include <linux/sysctl.h>
60 #define min(a, b) (((a) < (b)) ? (a) : (b))
70 #define HR(x, l) (SHA512_Update(&ctx, (char *)(x), (l)))
71 #define HD(x) (SHA512_Update(&ctx, (char *)&(x), sizeof (x)))
72 #define HF(x) (SHA512_Update(&ctx, (char *)&(x), sizeof (void*)))
74 int getentropy(void *buf, size_t len);
76 #ifdef CAN_REFERENCE_MAIN
77 extern int main(int, char *argv[]);
79 static int gotdata(char *buf, size_t len);
80 static int getentropy_urandom(void *buf, size_t len);
82 static int getentropy_sysctl(void *buf, size_t len);
84 static int getentropy_fallback(void *buf, size_t len);
87 getentropy(void *buf, size_t len)
97 /* try to use getrandom syscall introduced with kernel 3.17 */
98 ret = syscall(SYS_getrandom, buf, len, 0);
101 #endif /* SYS_getrandom */
104 * Try to get entropy with /dev/urandom
106 * This can fail if the process is inside a chroot or if file
107 * descriptors are exhausted.
109 ret = getentropy_urandom(buf, len);
115 * Try to use sysctl CTL_KERN, KERN_RANDOM, RANDOM_UUID.
116 * sysctl is a failsafe API, so it guarantees a result. This
117 * should work inside a chroot, or when file descriptors are
120 * However this can fail if the Linux kernel removes support
121 * for sysctl. Starting in 2007, there have been efforts to
122 * deprecate the sysctl API/ABI, and push callers towards use
123 * of the chroot-unavailable fd-using /proc mechanism --
124 * essentially the same problems as /dev/urandom.
126 * Numerous setbacks have been encountered in their deprecation
127 * schedule, so as of June 2014 the kernel ABI still exists on
128 * most Linux architectures. The sysctl() stub in libc is missing
129 * on some systems. There are also reports that some kernels
130 * spew messages to the console.
132 ret = getentropy_sysctl(buf, len);
135 #endif /* SYS__sysctl */
138 * Entropy collection via /dev/urandom and sysctl have failed.
140 * No other API exists for collecting entropy. See the large
141 * comment block above.
143 * We have very few options:
144 * - Even syslog_r is unsafe to call at this low level, so
145 * there is no way to alert the user or program.
146 * - Cannot call abort() because some systems have unsafe
148 * - Could raise(SIGKILL) resulting in silent program termination.
149 * - Return EIO, to hint that arc4random's stir function
150 * should raise(SIGKILL)
151 * - Do the best under the circumstances....
153 * This code path exists to bring light to the issue that Linux
154 * does not provide a failsafe API for entropy collection.
156 * We hope this demonstrates that Linux should either retain their
157 * sysctl ABI, or consider providing a new failsafe API which
158 * works in a chroot or when file descriptors are exhausted.
160 #undef FAIL_INSTEAD_OF_TRYING_FALLBACK
161 #ifdef FAIL_INSTEAD_OF_TRYING_FALLBACK
164 ret = getentropy_fallback(buf, len);
173 * Basic sanity checking; wish we could do better.
176 gotdata(char *buf, size_t len)
181 for (i = 0; i < len; ++i)
189 getentropy_urandom(void *buf, size_t len)
194 int save_errno = errno;
205 fd = open("/dev/urandom", flags, 0);
212 fcntl(fd, F_SETFD, fcntl(fd, F_GETFD) | FD_CLOEXEC);
215 /* Lightly verify that the device node looks sane */
216 if (fstat(fd, &st) == -1 || !S_ISCHR(st.st_mode)) {
220 if (ioctl(fd, RNDGETENTCNT, &cnt) == -1) {
224 for (i = 0; i < len; ) {
225 size_t wanted = len - i;
226 ssize_t ret = read(fd, (char*)buf + i, wanted);
229 if (errno == EAGAIN || errno == EINTR)
237 if (gotdata(buf, len) == 0) {
239 return 0; /* satisfied */
248 getentropy_sysctl(void *buf, size_t len)
250 static int mib[] = { CTL_KERN, KERN_RANDOM, RANDOM_UUID };
252 int save_errno = errno;
254 for (i = 0; i < len; ) {
255 size_t chunk = min(len - i, 16);
257 /* SYS__sysctl because some systems already removed sysctl() */
258 struct __sysctl_args args = {
264 if (syscall(SYS__sysctl, &args) != 0)
268 if (gotdata(buf, len) == 0) {
270 return (0); /* satisfied */
276 #endif /* SYS__sysctl */
280 #ifdef CLOCK_MONOTONIC
283 #ifdef CLOCK_MONOTONIC_RAW
295 #ifdef CLOCK_PROCESS_CPUTIME_ID
296 CLOCK_PROCESS_CPUTIME_ID,
298 #ifdef CLOCK_THREAD_CPUTIME_ID
299 CLOCK_THREAD_CPUTIME_ID,
304 getentropy_fallback(void *buf, size_t len)
306 uint8_t results[SHA512_DIGEST_LENGTH];
307 int save_errno = errno, e, pgs = getpagesize(), faster = 0, repeat;
315 static pid_t lastpid;
321 if (lastpid == pid) {
329 for (i = 0; i < len; ) {
332 for (j = 0; j < repeat; j++) {
333 HX((e = gettimeofday(&tv, NULL)) == -1, tv);
335 cnt += (int)tv.tv_sec;
336 cnt += (int)tv.tv_usec;
339 for (ii = 0; ii < sizeof(cl)/sizeof(cl[0]); ii++)
340 HX(clock_gettime(cl[ii], &ts) == -1, ts);
342 HX((pid = getpid()) == -1, pid);
343 HX((pid = getsid(pid)) == -1, pid);
344 HX((pid = getppid()) == -1, pid);
345 HX((pid = getpgid(0)) == -1, pid);
346 HX((e = getpriority(0, 0)) == -1, e);
351 (void) nanosleep(&ts, NULL);
354 HX(sigpending(&sigset) == -1, sigset);
355 HX(sigprocmask(SIG_BLOCK, NULL, &sigset) == -1,
358 #ifdef CAN_REFERENCE_MAIN
359 HF(main); /* an addr in program */
361 HF(getentropy); /* an addr in this library */
362 HF(printf); /* an addr in libc */
364 HD(p); /* an addr on stack */
366 HD(p); /* the addr of errno */
369 struct sockaddr_storage ss;
370 struct statvfs stvfs;
377 * Prime-sized mappings encourage fragmentation;
378 * thus exposing some address entropy.
384 { 17, MAP_FAILED }, { 3, MAP_FAILED },
385 { 11, MAP_FAILED }, { 2, MAP_FAILED },
386 { 5, MAP_FAILED }, { 3, MAP_FAILED },
387 { 7, MAP_FAILED }, { 1, MAP_FAILED },
388 { 57, MAP_FAILED }, { 3, MAP_FAILED },
389 { 131, MAP_FAILED }, { 1, MAP_FAILED },
392 for (m = 0; m < sizeof mm/sizeof(mm[0]); m++) {
393 HX(mm[m].p = mmap(NULL,
395 PROT_READ|PROT_WRITE,
396 MAP_PRIVATE|MAP_ANON, -1,
398 if (mm[m].p != MAP_FAILED) {
401 /* Touch some memory... */
404 (mm[m].npg * pgs - 1);
406 cnt += (int)((long)(mm[m].p)
410 /* Check cnts and times... */
411 for (ii = 0; ii < sizeof(cl)/sizeof(cl[0]);
413 HX((e = clock_gettime(cl[ii],
416 cnt += (int)ts.tv_nsec;
419 HX((e = getrusage(RUSAGE_SELF,
422 cnt += (int)ru.ru_utime.tv_sec;
423 cnt += (int)ru.ru_utime.tv_usec;
427 for (m = 0; m < sizeof mm/sizeof(mm[0]); m++) {
428 if (mm[m].p != MAP_FAILED)
429 munmap(mm[m].p, mm[m].npg * pgs);
430 mm[m].p = MAP_FAILED;
433 HX(stat(".", &st) == -1, st);
434 HX(statvfs(".", &stvfs) == -1, stvfs);
435 HX(statfs(".", &stfs) == -1, stfs);
437 HX(stat("/", &st) == -1, st);
438 HX(statvfs("/", &stvfs) == -1, stvfs);
439 HX(statfs("/", &stfs) == -1, stfs);
441 HX((e = fstat(0, &st)) == -1, st);
443 if (S_ISREG(st.st_mode) ||
444 S_ISFIFO(st.st_mode) ||
445 S_ISSOCK(st.st_mode)) {
446 HX(fstatvfs(0, &stvfs) == -1,
448 HX(fstatfs(0, &stfs) == -1,
450 HX((off = lseek(0, (off_t)0,
451 SEEK_CUR)) < 0, off);
453 if (S_ISCHR(st.st_mode)) {
454 HX(tcgetattr(0, &tios) == -1,
456 } else if (S_ISSOCK(st.st_mode)) {
457 memset(&ss, 0, sizeof ss);
460 (void *)&ss, &ssl) == -1,
465 HX((e = getrusage(RUSAGE_CHILDREN,
468 cnt += (int)ru.ru_utime.tv_sec;
469 cnt += (int)ru.ru_utime.tv_usec;
472 /* Subsequent hashes absorb previous result */
476 HX((e = gettimeofday(&tv, NULL)) == -1, tv);
478 cnt += (int)tv.tv_sec;
479 cnt += (int)tv.tv_usec;
484 #ifdef HAVE_GETAUXVAL
486 /* Not as random as you think but we take what we are given */
487 p = (char *) getauxval(AT_RANDOM);
491 # ifdef AT_SYSINFO_EHDR
492 p = (char *) getauxval(AT_SYSINFO_EHDR);
497 p = (char *) getauxval(AT_BASE);
501 #endif /* HAVE_GETAUXVAL */
503 SHA512_Final(results, &ctx);
504 memcpy((char*)buf + i, results, min(sizeof(results), len - i));
505 i += min(sizeof(results), len - i);
507 memset(results, 0, sizeof results);
508 if (gotdata(buf, len) == 0) {
510 return 0; /* satisfied */