1/*	$OpenBSD: getentropy_linux.c,v 1.48 2021/10/24 21:24:20 deraadt 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#include <openssl/sha.h>
51
52#include <linux/types.h>
53#include <linux/random.h>
54#ifdef HAVE_GETAUXVAL
55#include <sys/auxv.h>
56#endif
57#include <sys/vfs.h>
58
59#define REPEAT 5
60#define MINIMUM(a, b) (((a) < (b)) ? (a) : (b))
61
62#define HX(a, b) \
63	do { \
64		if ((a)) \
65			HD(errno); \
66		else \
67			HD(b); \
68	} while (0)
69
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*)))
73
74int	getentropy(void *buf, size_t len);
75
76#if defined(SYS_getrandom) && defined(GRND_NONBLOCK)
77static int getentropy_getrandom(void *buf, size_t len);
78#endif
79static int getentropy_urandom(void *buf, size_t len);
80#ifdef SYS__sysctl
81static int getentropy_sysctl(void *buf, size_t len);
82#endif
83static int getentropy_fallback(void *buf, size_t len);
84static int getentropy_phdr(struct dl_phdr_info *info, size_t size, void *data);
85
86int
87getentropy(void *buf, size_t len)
88{
89	int ret = -1;
90
91	if (len > 256) {
92		errno = EIO;
93		return (-1);
94	}
95
96#if defined(SYS_getrandom) && defined(GRND_NONBLOCK)
97	/*
98	 * Try descriptor-less getrandom(), in non-blocking mode.
99	 *
100	 * The design of Linux getrandom is broken.  It has an
101	 * uninitialized phase coupled with blocking behaviour, which
102	 * is unacceptable from within a library at boot time without
103	 * possible recovery. See http://bugs.python.org/issue26839#msg267745
104	 */
105	ret = getentropy_getrandom(buf, len);
106	if (ret != -1)
107		return (ret);
108#endif
109
110	/*
111	 * Try to get entropy with /dev/urandom
112	 *
113	 * This can fail if the process is inside a chroot or if file
114	 * descriptors are exhausted.
115	 */
116	ret = getentropy_urandom(buf, len);
117	if (ret != -1)
118		return (ret);
119
120#ifdef SYS__sysctl
121	/*
122	 * Try to use sysctl CTL_KERN, KERN_RANDOM, RANDOM_UUID.
123	 * sysctl is a failsafe API, so it guarantees a result.  This
124	 * should work inside a chroot, or when file descriptors are
125	 * exhausted.
126	 *
127	 * However this can fail if the Linux kernel removes support
128	 * for sysctl.  Starting in 2007, there have been efforts to
129	 * deprecate the sysctl API/ABI, and push callers towards use
130	 * of the chroot-unavailable fd-using /proc mechanism --
131	 * essentially the same problems as /dev/urandom.
132	 *
133	 * Numerous setbacks have been encountered in their deprecation
134	 * schedule, so as of June 2014 the kernel ABI still exists on
135	 * most Linux architectures. The sysctl() stub in libc is missing
136	 * on some systems.  There are also reports that some kernels
137	 * spew messages to the console.
138	 */
139	ret = getentropy_sysctl(buf, len);
140	if (ret != -1)
141		return (ret);
142#endif /* SYS__sysctl */
143
144	/*
145	 * Entropy collection via /dev/urandom and sysctl have failed.
146	 *
147	 * No other API exists for collecting entropy.  See the large
148	 * comment block above.
149	 *
150	 * We have very few options:
151	 *     - Even syslog_r is unsafe to call at this low level, so
152	 *	 there is no way to alert the user or program.
153	 *     - Cannot call abort() because some systems have unsafe
154	 *	 corefiles.
155	 *     - Could raise(SIGKILL) resulting in silent program termination.
156	 *     - Return EIO, to hint that arc4random's stir function
157	 *       should raise(SIGKILL)
158	 *     - Do the best under the circumstances....
159	 *
160	 * This code path exists to bring light to the issue that Linux
161	 * still does not provide a failsafe API for entropy collection.
162	 *
163	 * We hope this demonstrates that Linux should either retain their
164	 * sysctl ABI, or consider providing a new failsafe API which
165	 * works in a chroot or when file descriptors are exhausted.
166	 */
167#undef FAIL_INSTEAD_OF_TRYING_FALLBACK
168#ifdef FAIL_INSTEAD_OF_TRYING_FALLBACK
169	raise(SIGKILL);
170#endif
171	ret = getentropy_fallback(buf, len);
172	if (ret != -1)
173		return (ret);
174
175	errno = EIO;
176	return (ret);
177}
178
179#if defined(SYS_getrandom) && defined(GRND_NONBLOCK)
180static int
181getentropy_getrandom(void *buf, size_t len)
182{
183	int pre_errno = errno;
184	int ret;
185	if (len > 256)
186		return (-1);
187	do {
188		ret = syscall(SYS_getrandom, buf, len, GRND_NONBLOCK);
189	} while (ret == -1 && errno == EINTR);
190
191	if (ret != len)
192		return (-1);
193	errno = pre_errno;
194	return (0);
195}
196#endif
197
198static int
199getentropy_urandom(void *buf, size_t len)
200{
201	struct stat st;
202	size_t i;
203	int fd, cnt, flags;
204	int save_errno = errno;
205
206start:
207
208	flags = O_RDONLY;
209#ifdef O_NOFOLLOW
210	flags |= O_NOFOLLOW;
211#endif
212#ifdef O_CLOEXEC
213	flags |= O_CLOEXEC;
214#endif
215	fd = open("/dev/urandom", flags);
216	if (fd == -1) {
217		if (errno == EINTR)
218			goto start;
219		goto nodevrandom;
220	}
221#ifndef O_CLOEXEC
222	fcntl(fd, F_SETFD, fcntl(fd, F_GETFD) | FD_CLOEXEC);
223#endif
224
225	/* Lightly verify that the device node looks sane */
226	if (fstat(fd, &st) == -1 || !S_ISCHR(st.st_mode)) {
227		close(fd);
228		goto nodevrandom;
229	}
230	if (ioctl(fd, RNDGETENTCNT, &cnt) == -1) {
231		close(fd);
232		goto nodevrandom;
233	}
234	for (i = 0; i < len; ) {
235		size_t wanted = len - i;
236		ssize_t ret = read(fd, (char *)buf + i, wanted);
237
238		if (ret == -1) {
239			if (errno == EAGAIN || errno == EINTR)
240				continue;
241			close(fd);
242			goto nodevrandom;
243		}
244		i += ret;
245	}
246	close(fd);
247	errno = save_errno;
248	return (0);		/* satisfied */
249nodevrandom:
250	errno = EIO;
251	return (-1);
252}
253
254#ifdef SYS__sysctl
255static int
256getentropy_sysctl(void *buf, size_t len)
257{
258	static int mib[] = { CTL_KERN, KERN_RANDOM, RANDOM_UUID };
259	size_t i;
260	int save_errno = errno;
261
262	for (i = 0; i < len; ) {
263		size_t chunk = MINIMUM(len - i, 16);
264
265		/* SYS__sysctl because some systems already removed sysctl() */
266		struct __sysctl_args args = {
267			.name = mib,
268			.nlen = 3,
269			.oldval = (char *)buf + i,
270			.oldlenp = &chunk,
271		};
272		if (syscall(SYS__sysctl, &args) != 0)
273			goto sysctlfailed;
274		i += chunk;
275	}
276	errno = save_errno;
277	return (0);			/* satisfied */
278sysctlfailed:
279	errno = EIO;
280	return (-1);
281}
282#endif /* SYS__sysctl */
283
284static const int cl[] = {
285	CLOCK_REALTIME,
286#ifdef CLOCK_MONOTONIC
287	CLOCK_MONOTONIC,
288#endif
289#ifdef CLOCK_MONOTONIC_RAW
290	CLOCK_MONOTONIC_RAW,
291#endif
292#ifdef CLOCK_TAI
293	CLOCK_TAI,
294#endif
295#ifdef CLOCK_VIRTUAL
296	CLOCK_VIRTUAL,
297#endif
298#ifdef CLOCK_UPTIME
299	CLOCK_UPTIME,
300#endif
301#ifdef CLOCK_PROCESS_CPUTIME_ID
302	CLOCK_PROCESS_CPUTIME_ID,
303#endif
304#ifdef CLOCK_THREAD_CPUTIME_ID
305	CLOCK_THREAD_CPUTIME_ID,
306#endif
307};
308
309static int
310getentropy_phdr(struct dl_phdr_info *info, size_t size, void *data)
311{
312	SHA512_CTX *ctx = data;
313
314	SHA512_Update(ctx, &info->dlpi_addr, sizeof (info->dlpi_addr));
315	return (0);
316}
317
318static int
319getentropy_fallback(void *buf, size_t len)
320{
321	uint8_t results[SHA512_DIGEST_LENGTH];
322	int save_errno = errno, e, pgs = getpagesize(), faster = 0, repeat;
323	static int cnt;
324	struct timespec ts;
325	struct timeval tv;
326	struct rusage ru;
327	sigset_t sigset;
328	struct stat st;
329	SHA512_CTX ctx;
330	static pid_t lastpid;
331	pid_t pid;
332	size_t i, ii, m;
333	char *p;
334
335	pid = getpid();
336	if (lastpid == pid) {
337		faster = 1;
338		repeat = 2;
339	} else {
340		faster = 0;
341		lastpid = pid;
342		repeat = REPEAT;
343	}
344	for (i = 0; i < len; ) {
345		int j;
346		SHA512_Init(&ctx);
347		for (j = 0; j < repeat; j++) {
348			HX((e = gettimeofday(&tv, NULL)) == -1, tv);
349			if (e != -1) {
350				cnt += (int)tv.tv_sec;
351				cnt += (int)tv.tv_usec;
352			}
353
354			dl_iterate_phdr(getentropy_phdr, &ctx);
355
356			for (ii = 0; ii < sizeof(cl)/sizeof(cl[0]); ii++)
357				HX(clock_gettime(cl[ii], &ts) == -1, ts);
358
359			HX((pid = getpid()) == -1, pid);
360			HX((pid = getsid(pid)) == -1, pid);
361			HX((pid = getppid()) == -1, pid);
362			HX((pid = getpgid(0)) == -1, pid);
363			HX((e = getpriority(0, 0)) == -1, e);
364
365			if (!faster) {
366				ts.tv_sec = 0;
367				ts.tv_nsec = 1;
368				(void) nanosleep(&ts, NULL);
369			}
370
371			HX(sigpending(&sigset) == -1, sigset);
372			HX(sigprocmask(SIG_BLOCK, NULL, &sigset) == -1,
373			    sigset);
374
375			HF(getentropy);	/* an addr in this library */
376			HF(printf);		/* an addr in libc */
377			p = (char *)&p;
378			HD(p);		/* an addr on stack */
379			p = (char *)&errno;
380			HD(p);		/* the addr of errno */
381
382			if (i == 0) {
383				struct sockaddr_storage ss;
384				struct statvfs stvfs;
385				struct termios tios;
386				struct statfs stfs;
387				socklen_t ssl;
388				off_t off;
389
390				/*
391				 * Prime-sized mappings encourage fragmentation;
392				 * thus exposing some address entropy.
393				 */
394				struct mm {
395					size_t	npg;
396					void	*p;
397				} mm[] =	 {
398					{ 17, MAP_FAILED }, { 3, MAP_FAILED },
399					{ 11, MAP_FAILED }, { 2, MAP_FAILED },
400					{ 5, MAP_FAILED }, { 3, MAP_FAILED },
401					{ 7, MAP_FAILED }, { 1, MAP_FAILED },
402					{ 57, MAP_FAILED }, { 3, MAP_FAILED },
403					{ 131, MAP_FAILED }, { 1, MAP_FAILED },
404				};
405
406				for (m = 0; m < sizeof mm/sizeof(mm[0]); m++) {
407					HX(mm[m].p = mmap(NULL,
408					    mm[m].npg * pgs,
409					    PROT_READ|PROT_WRITE,
410					    MAP_PRIVATE|MAP_ANON, -1,
411					    (off_t)0), mm[m].p);
412					if (mm[m].p != MAP_FAILED) {
413						size_t mo;
414
415						/* Touch some memory... */
416						p = mm[m].p;
417						mo = cnt %
418						    (mm[m].npg * pgs - 1);
419						p[mo] = 1;
420						cnt += (int)((long)(mm[m].p)
421						    / pgs);
422					}
423
424					/* Check cnts and times... */
425					for (ii = 0; ii < sizeof(cl)/sizeof(cl[0]);
426					    ii++) {
427						HX((e = clock_gettime(cl[ii],
428						    &ts)) == -1, ts);
429						if (e != -1)
430							cnt += (int)ts.tv_nsec;
431					}
432
433					HX((e = getrusage(RUSAGE_SELF,
434					    &ru)) == -1, ru);
435					if (e != -1) {
436						cnt += (int)ru.ru_utime.tv_sec;
437						cnt += (int)ru.ru_utime.tv_usec;
438					}
439				}
440
441				for (m = 0; m < sizeof mm/sizeof(mm[0]); m++) {
442					if (mm[m].p != MAP_FAILED)
443						munmap(mm[m].p, mm[m].npg * pgs);
444					mm[m].p = MAP_FAILED;
445				}
446
447				HX(stat(".", &st) == -1, st);
448				HX(statvfs(".", &stvfs) == -1, stvfs);
449				HX(statfs(".", &stfs) == -1, stfs);
450
451				HX(stat("/", &st) == -1, st);
452				HX(statvfs("/", &stvfs) == -1, stvfs);
453				HX(statfs("/", &stfs) == -1, stfs);
454
455				HX((e = fstat(0, &st)) == -1, st);
456				if (e == -1) {
457					if (S_ISREG(st.st_mode) ||
458					    S_ISFIFO(st.st_mode) ||
459					    S_ISSOCK(st.st_mode)) {
460						HX(fstatvfs(0, &stvfs) == -1,
461						    stvfs);
462						HX(fstatfs(0, &stfs) == -1,
463						    stfs);
464						HX((off = lseek(0, (off_t)0,
465						    SEEK_CUR)) < 0, off);
466					}
467					if (S_ISCHR(st.st_mode)) {
468						HX(tcgetattr(0, &tios) == -1,
469						    tios);
470					} else if (S_ISSOCK(st.st_mode)) {
471						memset(&ss, 0, sizeof ss);
472						ssl = sizeof(ss);
473						HX(getpeername(0,
474						    (void *)&ss, &ssl) == -1,
475						    ss);
476					}
477				}
478
479				HX((e = getrusage(RUSAGE_CHILDREN,
480				    &ru)) == -1, ru);
481				if (e != -1) {
482					cnt += (int)ru.ru_utime.tv_sec;
483					cnt += (int)ru.ru_utime.tv_usec;
484				}
485			} else {
486				/* Subsequent hashes absorb previous result */
487				HD(results);
488			}
489
490			HX((e = gettimeofday(&tv, NULL)) == -1, tv);
491			if (e != -1) {
492				cnt += (int)tv.tv_sec;
493				cnt += (int)tv.tv_usec;
494			}
495
496			HD(cnt);
497		}
498#ifdef HAVE_GETAUXVAL
499#ifdef AT_RANDOM
500		/* Not as random as you think but we take what we are given */
501		p = (char *) getauxval(AT_RANDOM);
502		if (p)
503			HR(p, 16);
504#endif
505#ifdef AT_SYSINFO_EHDR
506		p = (char *) getauxval(AT_SYSINFO_EHDR);
507		if (p)
508			HR(p, pgs);
509#endif
510#ifdef AT_BASE
511		p = (char *) getauxval(AT_BASE);
512		if (p)
513			HD(p);
514#endif
515#endif
516
517		SHA512_Final(results, &ctx);
518		memcpy((char *)buf + i, results, MINIMUM(sizeof(results), len - i));
519		i += MINIMUM(sizeof(results), len - i);
520	}
521	explicit_bzero(&ctx, sizeof ctx);
522	explicit_bzero(results, sizeof results);
523	errno = save_errno;
524	return (0);		/* satisfied */
525}
526