1/*	$OpenBSD: getentropy_linux.c,v 1.28 2014/07/20 03:24:10 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://www.openbsd.org/cgi-bin/man.cgi/OpenBSD-current/man2/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 HAVE_SYS_SYSCTL_H
31#include <sys/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#ifdef HAVE_OPENSSL
51#include <openssl/sha.h>
52#endif
53
54#include <linux/random.h>
55#include <linux/sysctl.h>
56#ifdef HAVE_GETAUXVAL
57#include <sys/auxv.h>
58#endif
59#include <sys/vfs.h>
60
61#define REPEAT 5
62#define min(a, b) (((a) < (b)) ? (a) : (b))
63
64#define HX(a, b) \
65	do { \
66		if ((a)) \
67			HD(errno); \
68		else \
69			HD(b); \
70	} while (0)
71
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*)))
75
76int	getentropy(void *buf, size_t len);
77
78static int gotdata(char *buf, size_t len);
79#ifdef SYS__getrandom
80static int getentropy_getrandom(void *buf, size_t len);
81#endif
82static int getentropy_urandom(void *buf, size_t len);
83#ifdef SYS__sysctl
84static int getentropy_sysctl(void *buf, size_t len);
85#endif
86#ifdef HAVE_OPENSSL
87static int getentropy_fallback(void *buf, size_t len);
88static int getentropy_phdr(struct dl_phdr_info *info, size_t size, void *data);
89#endif
90
91int
92getentropy(void *buf, size_t len)
93{
94	int ret = -1;
95
96	if (len > 256) {
97		errno = EIO;
98		return -1;
99	}
100
101#ifdef SYS__getrandom
102	/*
103	 * Try descriptor-less getrandom()
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	 * exhuasted.
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	 * 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#ifdef HAVE_OPENSSL
172	ret = getentropy_fallback(buf, len);
173	if (ret != -1)
174		return (ret);
175#endif
176
177	errno = EIO;
178	return (ret);
179}
180
181/*
182 * Basic sanity checking; wish we could do better.
183 */
184static int
185gotdata(char *buf, size_t len)
186{
187	char	any_set = 0;
188	size_t	i;
189
190	for (i = 0; i < len; ++i)
191		any_set |= buf[i];
192	if (any_set == 0)
193		return -1;
194	return 0;
195}
196
197#ifdef SYS__getrandom
198static int
199getentropy_getrandom(void *buf, size_t len)
200{
201#if 0
202
203/* Hand-definitions until the API becomes commonplace */
204#ifndef SYS__getrandom
205#ifdef __LP64__
206#define SYS__getrandom 317
207#else
208#define SYS__getrandom 354
209#endif
210#endif
211	struct __getrandom_args args = {
212		.buf = buf;
213		.len = len;
214		.flags = 0;
215	};
216
217	if (len > 256)
218		return (-1);
219	ret = syscall(SYS__getrandom, &args);
220	if (ret == len)
221		return (0);
222#endif
223	return -1;
224}
225#endif
226
227static int
228getentropy_urandom(void *buf, size_t len)
229{
230	struct stat st;
231	size_t i;
232	int fd, cnt, flags;
233	int save_errno = errno;
234
235start:
236
237	flags = O_RDONLY;
238#ifdef O_NOFOLLOW
239	flags |= O_NOFOLLOW;
240#endif
241#ifdef O_CLOEXEC
242	flags |= O_CLOEXEC;
243#endif
244	fd = open("/dev/urandom", flags, 0);
245	if (fd == -1) {
246		if (errno == EINTR)
247			goto start;
248		goto nodevrandom;
249	}
250#ifndef O_CLOEXEC
251	fcntl(fd, F_SETFD, fcntl(fd, F_GETFD) | FD_CLOEXEC);
252#endif
253
254	/* Lightly verify that the device node looks sane */
255	if (fstat(fd, &st) == -1 || !S_ISCHR(st.st_mode)) {
256		close(fd);
257		goto nodevrandom;
258	}
259	if (ioctl(fd, RNDGETENTCNT, &cnt) == -1) {
260		close(fd);
261		goto nodevrandom;
262	}
263	for (i = 0; i < len; ) {
264		size_t wanted = len - i;
265		ssize_t ret = read(fd, (char *)buf + i, wanted);
266
267		if (ret == -1) {
268			if (errno == EAGAIN || errno == EINTR)
269				continue;
270			close(fd);
271			goto nodevrandom;
272		}
273		i += ret;
274	}
275	close(fd);
276	if (gotdata(buf, len) == 0) {
277		errno = save_errno;
278		return 0;		/* satisfied */
279	}
280nodevrandom:
281	errno = EIO;
282	return -1;
283}
284
285#ifdef SYS__sysctl
286static int
287getentropy_sysctl(void *buf, size_t len)
288{
289	static int mib[] = { CTL_KERN, KERN_RANDOM, RANDOM_UUID };
290	size_t i;
291	int save_errno = errno;
292
293	for (i = 0; i < len; ) {
294		size_t chunk = min(len - i, 16);
295
296		/* SYS__sysctl because some systems already removed sysctl() */
297		struct __sysctl_args args = {
298			.name = mib,
299			.nlen = 3,
300			.oldval = (char*) buf + i,
301			.oldlenp = &chunk,
302		};
303		if (syscall(SYS__sysctl, &args) != 0)
304			goto sysctlfailed;
305		i += chunk;
306	}
307	if (gotdata(buf, len) == 0) {
308		errno = save_errno;
309		return (0);			/* satisfied */
310	}
311sysctlfailed:
312	errno = EIO;
313	return -1;
314}
315#endif /* SYS__sysctl */
316
317#ifdef HAVE_OPENSSL
318
319static int cl[] = {
320	CLOCK_REALTIME,
321#ifdef CLOCK_MONOTONIC
322	CLOCK_MONOTONIC,
323#endif
324#ifdef CLOCK_MONOTONIC_RAW
325	CLOCK_MONOTONIC_RAW,
326#endif
327#ifdef CLOCK_TAI
328	CLOCK_TAI,
329#endif
330#ifdef CLOCK_VIRTUAL
331	CLOCK_VIRTUAL,
332#endif
333#ifdef CLOCK_UPTIME
334	CLOCK_UPTIME,
335#endif
336#ifdef CLOCK_PROCESS_CPUTIME_ID
337	CLOCK_PROCESS_CPUTIME_ID,
338#endif
339#ifdef CLOCK_THREAD_CPUTIME_ID
340	CLOCK_THREAD_CPUTIME_ID,
341#endif
342};
343
344static int
345getentropy_phdr(struct dl_phdr_info *info, size_t size, void *data)
346{
347	SHA512_CTX *ctx = data;
348
349	SHA512_Update(ctx, &info->dlpi_addr, sizeof (info->dlpi_addr));
350	return 0;
351}
352
353static int
354getentropy_fallback(void *buf, size_t len)
355{
356	uint8_t results[SHA512_DIGEST_LENGTH];
357	int save_errno = errno, e, pgs = getpagesize(), faster = 0, repeat;
358	static int cnt;
359	struct timespec ts;
360	struct timeval tv;
361	struct rusage ru;
362	sigset_t sigset;
363	struct stat st;
364	SHA512_CTX ctx;
365	static pid_t lastpid;
366	pid_t pid;
367	size_t i, ii, m;
368	char *p;
369
370	pid = getpid();
371	if (lastpid == pid) {
372		faster = 1;
373		repeat = 2;
374	} else {
375		faster = 0;
376		lastpid = pid;
377		repeat = REPEAT;
378	}
379	for (i = 0; i < len; ) {
380		int j;
381		SHA512_Init(&ctx);
382		for (j = 0; j < repeat; j++) {
383			HX((e = gettimeofday(&tv, NULL)) == -1, tv);
384			if (e != -1) {
385				cnt += (int)tv.tv_sec;
386				cnt += (int)tv.tv_usec;
387			}
388
389			dl_iterate_phdr(getentropy_phdr, &ctx);
390
391			for (ii = 0; ii < sizeof(cl)/sizeof(cl[0]); ii++)
392				HX(clock_gettime(cl[ii], &ts) == -1, ts);
393
394			HX((pid = getpid()) == -1, pid);
395			HX((pid = getsid(pid)) == -1, pid);
396			HX((pid = getppid()) == -1, pid);
397			HX((pid = getpgid(0)) == -1, pid);
398			HX((e = getpriority(0, 0)) == -1, e);
399
400			if (!faster) {
401				ts.tv_sec = 0;
402				ts.tv_nsec = 1;
403				(void) nanosleep(&ts, NULL);
404			}
405
406			HX(sigpending(&sigset) == -1, sigset);
407			HX(sigprocmask(SIG_BLOCK, NULL, &sigset) == -1,
408			    sigset);
409
410			HF(getentropy);	/* an addr in this library */
411			HF(printf);		/* an addr in libc */
412			p = (char *)&p;
413			HD(p);		/* an addr on stack */
414			p = (char *)&errno;
415			HD(p);		/* the addr of errno */
416
417			if (i == 0) {
418				struct sockaddr_storage ss;
419				struct statvfs stvfs;
420				struct termios tios;
421				struct statfs stfs;
422				socklen_t ssl;
423				off_t off;
424
425				/*
426				 * Prime-sized mappings encourage fragmentation;
427				 * thus exposing some address entropy.
428				 */
429				struct mm {
430					size_t	npg;
431					void	*p;
432				} mm[] =	 {
433					{ 17, MAP_FAILED }, { 3, MAP_FAILED },
434					{ 11, MAP_FAILED }, { 2, MAP_FAILED },
435					{ 5, MAP_FAILED }, { 3, MAP_FAILED },
436					{ 7, MAP_FAILED }, { 1, MAP_FAILED },
437					{ 57, MAP_FAILED }, { 3, MAP_FAILED },
438					{ 131, MAP_FAILED }, { 1, MAP_FAILED },
439				};
440
441				for (m = 0; m < sizeof mm/sizeof(mm[0]); m++) {
442					HX(mm[m].p = mmap(NULL,
443					    mm[m].npg * pgs,
444					    PROT_READ|PROT_WRITE,
445					    MAP_PRIVATE|MAP_ANON, -1,
446					    (off_t)0), mm[m].p);
447					if (mm[m].p != MAP_FAILED) {
448						size_t mo;
449
450						/* Touch some memory... */
451						p = mm[m].p;
452						mo = cnt %
453						    (mm[m].npg * pgs - 1);
454						p[mo] = 1;
455						cnt += (int)((long)(mm[m].p)
456						    / pgs);
457					}
458
459					/* Check cnts and times... */
460					for (ii = 0; ii < sizeof(cl)/sizeof(cl[0]);
461					    ii++) {
462						HX((e = clock_gettime(cl[ii],
463						    &ts)) == -1, ts);
464						if (e != -1)
465							cnt += (int)ts.tv_nsec;
466					}
467
468					HX((e = getrusage(RUSAGE_SELF,
469					    &ru)) == -1, ru);
470					if (e != -1) {
471						cnt += (int)ru.ru_utime.tv_sec;
472						cnt += (int)ru.ru_utime.tv_usec;
473					}
474				}
475
476				for (m = 0; m < sizeof mm/sizeof(mm[0]); m++) {
477					if (mm[m].p != MAP_FAILED)
478						munmap(mm[m].p, mm[m].npg * pgs);
479					mm[m].p = MAP_FAILED;
480				}
481
482				HX(stat(".", &st) == -1, st);
483				HX(statvfs(".", &stvfs) == -1, stvfs);
484				HX(statfs(".", &stfs) == -1, stfs);
485
486				HX(stat("/", &st) == -1, st);
487				HX(statvfs("/", &stvfs) == -1, stvfs);
488				HX(statfs("/", &stfs) == -1, stfs);
489
490				HX((e = fstat(0, &st)) == -1, st);
491				if (e == -1) {
492					if (S_ISREG(st.st_mode) ||
493					    S_ISFIFO(st.st_mode) ||
494					    S_ISSOCK(st.st_mode)) {
495						HX(fstatvfs(0, &stvfs) == -1,
496						    stvfs);
497						HX(fstatfs(0, &stfs) == -1,
498						    stfs);
499						HX((off = lseek(0, (off_t)0,
500						    SEEK_CUR)) < 0, off);
501					}
502					if (S_ISCHR(st.st_mode)) {
503						HX(tcgetattr(0, &tios) == -1,
504						    tios);
505					} else if (S_ISSOCK(st.st_mode)) {
506						memset(&ss, 0, sizeof ss);
507						ssl = sizeof(ss);
508						HX(getpeername(0,
509						    (void *)&ss, &ssl) == -1,
510						    ss);
511					}
512				}
513
514				HX((e = getrusage(RUSAGE_CHILDREN,
515				    &ru)) == -1, ru);
516				if (e != -1) {
517					cnt += (int)ru.ru_utime.tv_sec;
518					cnt += (int)ru.ru_utime.tv_usec;
519				}
520			} else {
521				/* Subsequent hashes absorb previous result */
522				HD(results);
523			}
524
525			HX((e = gettimeofday(&tv, NULL)) == -1, tv);
526			if (e != -1) {
527				cnt += (int)tv.tv_sec;
528				cnt += (int)tv.tv_usec;
529			}
530
531			HD(cnt);
532		}
533#ifdef HAVE_GETAUXVAL
534#ifdef AT_RANDOM
535		/* Not as random as you think but we take what we are given */
536		p = (char *) getauxval(AT_RANDOM);
537		if (p)
538			HR(p, 16);
539#endif
540#ifdef AT_SYSINFO_EHDR
541		p = (char *) getauxval(AT_SYSINFO_EHDR);
542		if (p)
543			HR(p, pgs);
544#endif
545#ifdef AT_BASE
546		p = (char *) getauxval(AT_BASE);
547		if (p)
548			HD(p);
549#endif
550#endif
551
552		SHA512_Final(results, &ctx);
553		memcpy((char *)buf + i, results, min(sizeof(results), len - i));
554		i += min(sizeof(results), len - i);
555	}
556	memset(results, 0, sizeof results);
557	if (gotdata(buf, len) == 0) {
558		errno = save_errno;
559		return 0;		/* satisfied */
560	}
561	errno = EIO;
562	return -1;
563}
564
565#endif /* HAVE_OPENSSL */
566