getentropy_solaris.c revision 285206 
1/*	$OpenBSD: getentropy_solaris.c,v 1.3 2014/07/12 14:46:31 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#include "config.h"
20
21#include <sys/types.h>
22#include <sys/param.h>
23#include <sys/ioctl.h>
24#include <sys/resource.h>
25#include <sys/syscall.h>
26#include <sys/statvfs.h>
27#include <sys/socket.h>
28#include <sys/mount.h>
29#include <sys/mman.h>
30#include <sys/stat.h>
31#include <sys/time.h>
32#include <stdlib.h>
33#include <stdint.h>
34#include <stdio.h>
35#include <termios.h>
36#include <fcntl.h>
37#include <signal.h>
38#include <string.h>
39#include <errno.h>
40#include <unistd.h>
41#include <time.h>
42#include <sys/sha2.h>
43#define SHA512_Init SHA512Init
44#define SHA512_Update SHA512Update
45#define SHA512_Final SHA512Final
46
47#include <sys/vfs.h>
48#include <sys/statfs.h>
49#include <sys/loadavg.h>
50
51#define REPEAT 5
52#define min(a, b) (((a) < (b)) ? (a) : (b))
53
54#define HX(a, b) \
55	do { \
56		if ((a)) \
57			HD(errno); \
58		else \
59			HD(b); \
60	} while (0)
61
62#define HR(x, l) (SHA512_Update(&ctx, (char *)(x), (l)))
63#define HD(x)	 (SHA512_Update(&ctx, (char *)&(x), sizeof (x)))
64#define HF(x)	 (SHA512_Update(&ctx, (char *)&(x), sizeof (void*)))
65
66int	getentropy(void *buf, size_t len);
67
68#ifdef CAN_REFERENCE_MAIN
69extern int main(int, char *argv[]);
70#endif
71static int gotdata(char *buf, size_t len);
72static int getentropy_urandom(void *buf, size_t len, const char *path,
73    int devfscheck);
74static int getentropy_fallback(void *buf, size_t len);
75
76int
77getentropy(void *buf, size_t len)
78{
79	int ret = -1;
80
81	if (len > 256) {
82		errno = EIO;
83		return -1;
84	}
85
86	/*
87	 * Try to get entropy with /dev/urandom
88	 *
89	 * Solaris provides /dev/urandom as a symbolic link to
90	 * /devices/pseudo/random@0:urandom which is provided by
91	 * a devfs filesystem.  Best practice is to use O_NOFOLLOW,
92	 * so we must try the unpublished name directly.
93	 *
94	 * This can fail if the process is inside a chroot which lacks
95	 * the devfs mount, or if file descriptors are exhausted.
96	 */
97	ret = getentropy_urandom(buf, len,
98	    "/devices/pseudo/random@0:urandom", 1);
99	if (ret != -1)
100		return (ret);
101
102	/*
103	 * Unfortunately, chroot spaces on Solaris are sometimes setup
104	 * with direct device node of the well-known /dev/urandom name
105	 * (perhaps to avoid dragging all of devfs into the space).
106	 *
107	 * This can fail if the process is inside a chroot or if file
108	 * descriptors are exhausted.
109	 */
110	ret = getentropy_urandom(buf, len, "/dev/urandom", 0);
111	if (ret != -1)
112		return (ret);
113
114	/*
115	 * Entropy collection via /dev/urandom has failed.
116	 *
117	 * No other API exists for collecting entropy, and we have
118	 * no failsafe way to get it on Solaris that is not sensitive
119	 * to resource exhaustion.
120	 *
121	 * We have very few options:
122	 *     - Even syslog_r is unsafe to call at this low level, so
123	 *	 there is no way to alert the user or program.
124	 *     - Cannot call abort() because some systems have unsafe
125	 *	 corefiles.
126	 *     - Could raise(SIGKILL) resulting in silent program termination.
127	 *     - Return EIO, to hint that arc4random's stir function
128	 *       should raise(SIGKILL)
129	 *     - Do the best under the circumstances....
130	 *
131	 * This code path exists to bring light to the issue that Solaris
132	 * does not provide a failsafe API for entropy collection.
133	 *
134	 * We hope this demonstrates that Solaris should consider
135	 * providing a new failsafe API which works in a chroot or
136	 * when file descriptors are exhausted.
137	 */
138#undef FAIL_INSTEAD_OF_TRYING_FALLBACK
139#ifdef FAIL_INSTEAD_OF_TRYING_FALLBACK
140	raise(SIGKILL);
141#endif
142	ret = getentropy_fallback(buf, len);
143	if (ret != -1)
144		return (ret);
145
146	errno = EIO;
147	return (ret);
148}
149
150/*
151 * Basic sanity checking; wish we could do better.
152 */
153static int
154gotdata(char *buf, size_t len)
155{
156	char	any_set = 0;
157	size_t	i;
158
159	for (i = 0; i < len; ++i)
160		any_set |= buf[i];
161	if (any_set == 0)
162		return -1;
163	return 0;
164}
165
166static int
167getentropy_urandom(void *buf, size_t len, const char *path, int devfscheck)
168{
169	struct stat st;
170	size_t i;
171	int fd, flags;
172	int save_errno = errno;
173
174start:
175
176	flags = O_RDONLY;
177#ifdef O_NOFOLLOW
178	flags |= O_NOFOLLOW;
179#endif
180#ifdef O_CLOEXEC
181	flags |= O_CLOEXEC;
182#endif
183	fd = open(path, flags, 0);
184	if (fd == -1) {
185		if (errno == EINTR)
186			goto start;
187		goto nodevrandom;
188	}
189#ifndef O_CLOEXEC
190	fcntl(fd, F_SETFD, fcntl(fd, F_GETFD) | FD_CLOEXEC);
191#endif
192
193	/* Lightly verify that the device node looks sane */
194	if (fstat(fd, &st) == -1 || !S_ISCHR(st.st_mode) ||
195	    (devfscheck && (strcmp(st.st_fstype, "devfs") != 0))) {
196		close(fd);
197		goto nodevrandom;
198	}
199	for (i = 0; i < len; ) {
200		size_t wanted = len - i;
201		ssize_t ret = read(fd, (char*)buf + i, wanted);
202
203		if (ret == -1) {
204			if (errno == EAGAIN || errno == EINTR)
205				continue;
206			close(fd);
207			goto nodevrandom;
208		}
209		i += ret;
210	}
211	close(fd);
212	if (gotdata(buf, len) == 0) {
213		errno = save_errno;
214		return 0;		/* satisfied */
215	}
216nodevrandom:
217	errno = EIO;
218	return -1;
219}
220
221static const int cl[] = {
222	CLOCK_REALTIME,
223#ifdef CLOCK_MONOTONIC
224	CLOCK_MONOTONIC,
225#endif
226#ifdef CLOCK_MONOTONIC_RAW
227	CLOCK_MONOTONIC_RAW,
228#endif
229#ifdef CLOCK_TAI
230	CLOCK_TAI,
231#endif
232#ifdef CLOCK_VIRTUAL
233	CLOCK_VIRTUAL,
234#endif
235#ifdef CLOCK_UPTIME
236	CLOCK_UPTIME,
237#endif
238#ifdef CLOCK_PROCESS_CPUTIME_ID
239	CLOCK_PROCESS_CPUTIME_ID,
240#endif
241#ifdef CLOCK_THREAD_CPUTIME_ID
242	CLOCK_THREAD_CPUTIME_ID,
243#endif
244};
245
246static int
247getentropy_fallback(void *buf, size_t len)
248{
249	uint8_t results[SHA512_DIGEST_LENGTH];
250	int save_errno = errno, e, pgs = getpagesize(), faster = 0, repeat;
251	static int cnt;
252	struct timespec ts;
253	struct timeval tv;
254	double loadavg[3];
255	struct rusage ru;
256	sigset_t sigset;
257	struct stat st;
258	SHA512_CTX ctx;
259	static pid_t lastpid;
260	pid_t pid;
261	size_t i, ii, m;
262	char *p;
263
264	pid = getpid();
265	if (lastpid == pid) {
266		faster = 1;
267		repeat = 2;
268	} else {
269		faster = 0;
270		lastpid = pid;
271		repeat = REPEAT;
272	}
273	for (i = 0; i < len; ) {
274		int j;
275		SHA512_Init(&ctx);
276		for (j = 0; j < repeat; j++) {
277			HX((e = gettimeofday(&tv, NULL)) == -1, tv);
278			if (e != -1) {
279				cnt += (int)tv.tv_sec;
280				cnt += (int)tv.tv_usec;
281			}
282
283			for (ii = 0; ii < sizeof(cl)/sizeof(cl[0]); ii++)
284				HX(clock_gettime(cl[ii], &ts) == -1, ts);
285
286			HX((pid = getpid()) == -1, pid);
287			HX((pid = getsid(pid)) == -1, pid);
288			HX((pid = getppid()) == -1, pid);
289			HX((pid = getpgid(0)) == -1, pid);
290			HX((e = getpriority(0, 0)) == -1, e);
291			HX((getloadavg(loadavg, 3) == -1), loadavg);
292
293			if (!faster) {
294				ts.tv_sec = 0;
295				ts.tv_nsec = 1;
296				(void) nanosleep(&ts, NULL);
297			}
298
299			HX(sigpending(&sigset) == -1, sigset);
300			HX(sigprocmask(SIG_BLOCK, NULL, &sigset) == -1,
301			    sigset);
302
303#ifdef CAN_REFERENCE_MAIN
304			HF(main);		/* an addr in program */
305#endif
306			HF(getentropy);	/* an addr in this library */
307			HF(printf);		/* an addr in libc */
308			p = (char *)&p;
309			HD(p);		/* an addr on stack */
310			p = (char *)&errno;
311			HD(p);		/* the addr of errno */
312
313			if (i == 0) {
314				struct sockaddr_storage ss;
315				struct statvfs stvfs;
316				struct termios tios;
317				socklen_t ssl;
318				off_t off;
319
320				/*
321				 * Prime-sized mappings encourage fragmentation;
322				 * thus exposing some address entropy.
323				 */
324				struct mm {
325					size_t	npg;
326					void	*p;
327				} mm[] =	 {
328					{ 17, MAP_FAILED }, { 3, MAP_FAILED },
329					{ 11, MAP_FAILED }, { 2, MAP_FAILED },
330					{ 5, MAP_FAILED }, { 3, MAP_FAILED },
331					{ 7, MAP_FAILED }, { 1, MAP_FAILED },
332					{ 57, MAP_FAILED }, { 3, MAP_FAILED },
333					{ 131, MAP_FAILED }, { 1, MAP_FAILED },
334				};
335
336				for (m = 0; m < sizeof mm/sizeof(mm[0]); m++) {
337					HX(mm[m].p = mmap(NULL,
338					    mm[m].npg * pgs,
339					    PROT_READ|PROT_WRITE,
340					    MAP_PRIVATE|MAP_ANON, -1,
341					    (off_t)0), mm[m].p);
342					if (mm[m].p != MAP_FAILED) {
343						size_t mo;
344
345						/* Touch some memory... */
346						p = mm[m].p;
347						mo = cnt %
348						    (mm[m].npg * pgs - 1);
349						p[mo] = 1;
350						cnt += (int)((long)(mm[m].p)
351						    / pgs);
352					}
353
354					/* Check cnts and times... */
355					for (ii = 0; ii < sizeof(cl)/sizeof(cl[0]);
356					    ii++) {
357						HX((e = clock_gettime(cl[ii],
358						    &ts)) == -1, ts);
359						if (e != -1)
360							cnt += (int)ts.tv_nsec;
361					}
362
363					HX((e = getrusage(RUSAGE_SELF,
364					    &ru)) == -1, ru);
365					if (e != -1) {
366						cnt += (int)ru.ru_utime.tv_sec;
367						cnt += (int)ru.ru_utime.tv_usec;
368					}
369				}
370
371				for (m = 0; m < sizeof mm/sizeof(mm[0]); m++) {
372					if (mm[m].p != MAP_FAILED)
373						munmap(mm[m].p, mm[m].npg * pgs);
374					mm[m].p = MAP_FAILED;
375				}
376
377				HX(stat(".", &st) == -1, st);
378				HX(statvfs(".", &stvfs) == -1, stvfs);
379
380				HX(stat("/", &st) == -1, st);
381				HX(statvfs("/", &stvfs) == -1, stvfs);
382
383				HX((e = fstat(0, &st)) == -1, st);
384				if (e == -1) {
385					if (S_ISREG(st.st_mode) ||
386					    S_ISFIFO(st.st_mode) ||
387					    S_ISSOCK(st.st_mode)) {
388						HX(fstatvfs(0, &stvfs) == -1,
389						    stvfs);
390						HX((off = lseek(0, (off_t)0,
391						    SEEK_CUR)) < 0, off);
392					}
393					if (S_ISCHR(st.st_mode)) {
394						HX(tcgetattr(0, &tios) == -1,
395						    tios);
396					} else if (S_ISSOCK(st.st_mode)) {
397						memset(&ss, 0, sizeof ss);
398						ssl = sizeof(ss);
399						HX(getpeername(0,
400						    (void *)&ss, &ssl) == -1,
401						    ss);
402					}
403				}
404
405				HX((e = getrusage(RUSAGE_CHILDREN,
406				    &ru)) == -1, ru);
407				if (e != -1) {
408					cnt += (int)ru.ru_utime.tv_sec;
409					cnt += (int)ru.ru_utime.tv_usec;
410				}
411			} else {
412				/* Subsequent hashes absorb previous result */
413				HD(results);
414			}
415
416			HX((e = gettimeofday(&tv, NULL)) == -1, tv);
417			if (e != -1) {
418				cnt += (int)tv.tv_sec;
419				cnt += (int)tv.tv_usec;
420			}
421
422			HD(cnt);
423		}
424		SHA512_Final(results, &ctx);
425		memcpy((char*)buf + i, results, min(sizeof(results), len - i));
426		i += min(sizeof(results), len - i);
427	}
428	memset(results, 0, sizeof results);
429	if (gotdata(buf, len) == 0) {
430		errno = save_errno;
431		return 0;		/* satisfied */
432	}
433	errno = EIO;
434	return -1;
435}
436