getentropy_solaris.c revision 356345 
1/*	$OpenBSD: getentropy_solaris.c,v 1.13 2018/11/20 08:04:28 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#include "config.h"
24#include <sys/types.h>
25#include <sys/param.h>
26#include <sys/ioctl.h>
27#include <sys/resource.h>
28#include <sys/syscall.h>
29#include <sys/statvfs.h>
30#include <sys/socket.h>
31#include <sys/mount.h>
32#include <sys/mman.h>
33#include <sys/stat.h>
34#include <sys/time.h>
35#include <stdlib.h>
36#ifdef HAVE_STDINT_H
37#include <stdint.h>
38#endif
39#include <stdio.h>
40#include <link.h>
41#include <termios.h>
42#include <fcntl.h>
43#include <signal.h>
44#include <string.h>
45#include <errno.h>
46#include <unistd.h>
47#include <time.h>
48#ifdef HAVE_SYS_SHA2_H
49#include <sys/sha2.h>
50#define SHA512_Init SHA512Init
51#define SHA512_Update SHA512Update
52#define SHA512_Final SHA512Final
53#else
54#include "openssl/sha.h"
55#endif
56
57#include <sys/vfs.h>
58#include <sys/statfs.h>
59#include <sys/loadavg.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 getentropy_urandom(void *buf, size_t len, const char *path,
79    int devfscheck);
80static int getentropy_fallback(void *buf, size_t len);
81static int getentropy_phdr(struct dl_phdr_info *info, size_t size, void *data);
82
83int
84getentropy(void *buf, size_t len)
85{
86	int ret = -1;
87
88	if (len > 256) {
89		errno = EIO;
90		return (-1);
91	}
92
93	/*
94	 * Try to get entropy with /dev/urandom
95	 *
96	 * Solaris provides /dev/urandom as a symbolic link to
97	 * /devices/pseudo/random@0:urandom which is provided by
98	 * a devfs filesystem.  Best practice is to use O_NOFOLLOW,
99	 * so we must try the unpublished name directly.
100	 *
101	 * This can fail if the process is inside a chroot which lacks
102	 * the devfs mount, or if file descriptors are exhausted.
103	 */
104	ret = getentropy_urandom(buf, len,
105	    "/devices/pseudo/random@0:urandom", 1);
106	if (ret != -1)
107		return (ret);
108
109	/*
110	 * Unfortunately, chroot spaces on Solaris are sometimes setup
111	 * with direct device node of the well-known /dev/urandom name
112	 * (perhaps to avoid dragging all of devfs into the space).
113	 *
114	 * This can fail if the process is inside a chroot or if file
115	 * descriptors are exhausted.
116	 */
117	ret = getentropy_urandom(buf, len, "/dev/urandom", 0);
118	if (ret != -1)
119		return (ret);
120
121	/*
122	 * Entropy collection via /dev/urandom has failed.
123	 *
124	 * No other API exists for collecting entropy, and we have
125	 * no failsafe way to get it on Solaris that is not sensitive
126	 * to resource exhaustion.
127	 *
128	 * We have very few options:
129	 *     - Even syslog_r is unsafe to call at this low level, so
130	 *	 there is no way to alert the user or program.
131	 *     - Cannot call abort() because some systems have unsafe
132	 *	 corefiles.
133	 *     - Could raise(SIGKILL) resulting in silent program termination.
134	 *     - Return EIO, to hint that arc4random's stir function
135	 *       should raise(SIGKILL)
136	 *     - Do the best under the circumstances....
137	 *
138	 * This code path exists to bring light to the issue that Solaris
139	 * does not provide a failsafe API for entropy collection.
140	 *
141	 * We hope this demonstrates that Solaris should consider
142	 * providing a new failsafe API which works in a chroot or
143	 * when file descriptors are exhausted.
144	 */
145#undef FAIL_INSTEAD_OF_TRYING_FALLBACK
146#ifdef FAIL_INSTEAD_OF_TRYING_FALLBACK
147	raise(SIGKILL);
148#endif
149	ret = getentropy_fallback(buf, len);
150	if (ret != -1)
151		return (ret);
152
153	errno = EIO;
154	return (ret);
155}
156
157static int
158getentropy_urandom(void *buf, size_t len, const char *path, int devfscheck)
159{
160	struct stat st;
161	size_t i;
162	int fd, flags;
163	int save_errno = errno;
164
165start:
166
167	flags = O_RDONLY;
168#ifdef O_NOFOLLOW
169	flags |= O_NOFOLLOW;
170#endif
171#ifdef O_CLOEXEC
172	flags |= O_CLOEXEC;
173#endif
174	fd = open(path, flags, 0);
175	if (fd == -1) {
176		if (errno == EINTR)
177			goto start;
178		goto nodevrandom;
179	}
180#ifndef O_CLOEXEC
181	fcntl(fd, F_SETFD, fcntl(fd, F_GETFD) | FD_CLOEXEC);
182#endif
183
184	/* Lightly verify that the device node looks sane */
185	if (fstat(fd, &st) == -1 || !S_ISCHR(st.st_mode) ||
186	    (devfscheck && (strcmp(st.st_fstype, "devfs") != 0))) {
187		close(fd);
188		goto nodevrandom;
189	}
190	for (i = 0; i < len; ) {
191		size_t wanted = len - i;
192		ssize_t ret = read(fd, (char *)buf + i, wanted);
193
194		if (ret == -1) {
195			if (errno == EAGAIN || errno == EINTR)
196				continue;
197			close(fd);
198			goto nodevrandom;
199		}
200		i += ret;
201	}
202	close(fd);
203	errno = save_errno;
204	return (0);		/* satisfied */
205nodevrandom:
206	errno = EIO;
207	return (-1);
208}
209
210static const int cl[] = {
211	CLOCK_REALTIME,
212#ifdef CLOCK_MONOTONIC
213	CLOCK_MONOTONIC,
214#endif
215#ifdef CLOCK_MONOTONIC_RAW
216	CLOCK_MONOTONIC_RAW,
217#endif
218#ifdef CLOCK_TAI
219	CLOCK_TAI,
220#endif
221#ifdef CLOCK_VIRTUAL
222	CLOCK_VIRTUAL,
223#endif
224#ifdef CLOCK_UPTIME
225	CLOCK_UPTIME,
226#endif
227#ifdef CLOCK_PROCESS_CPUTIME_ID
228	CLOCK_PROCESS_CPUTIME_ID,
229#endif
230#ifdef CLOCK_THREAD_CPUTIME_ID
231	CLOCK_THREAD_CPUTIME_ID,
232#endif
233};
234
235static int
236getentropy_phdr(struct dl_phdr_info *info, size_t size, void *data)
237{
238	SHA512_CTX *ctx = data;
239
240	SHA512_Update(ctx, &info->dlpi_addr, sizeof (info->dlpi_addr));
241	return (0);
242}
243
244static int
245getentropy_fallback(void *buf, size_t len)
246{
247	uint8_t results[SHA512_DIGEST_LENGTH];
248	int save_errno = errno, e, pgs = getpagesize(), faster = 0, repeat;
249	static int cnt;
250	struct timespec ts;
251	struct timeval tv;
252	double loadavg[3];
253	struct rusage ru;
254	sigset_t sigset;
255	struct stat st;
256	SHA512_CTX ctx;
257	static pid_t lastpid;
258	pid_t pid;
259	size_t i, ii, m;
260	char *p;
261
262	pid = getpid();
263	if (lastpid == pid) {
264		faster = 1;
265		repeat = 2;
266	} else {
267		faster = 0;
268		lastpid = pid;
269		repeat = REPEAT;
270	}
271	for (i = 0; i < len; ) {
272		int j;
273		SHA512_Init(&ctx);
274		for (j = 0; j < repeat; j++) {
275			HX((e = gettimeofday(&tv, NULL)) == -1, tv);
276			if (e != -1) {
277				cnt += (int)tv.tv_sec;
278				cnt += (int)tv.tv_usec;
279			}
280
281			dl_iterate_phdr(getentropy_phdr, &ctx);
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			HF(getentropy);	/* an addr in this library */
304			HF(printf);		/* an addr in libc */
305			p = (char *)&p;
306			HD(p);		/* an addr on stack */
307			p = (char *)&errno;
308			HD(p);		/* the addr of errno */
309
310			if (i == 0) {
311				struct sockaddr_storage ss;
312				struct statvfs stvfs;
313				struct termios tios;
314				socklen_t ssl;
315				off_t off;
316
317				/*
318				 * Prime-sized mappings encourage fragmentation;
319				 * thus exposing some address entropy.
320				 */
321				struct mm {
322					size_t	npg;
323					void	*p;
324				} mm[] =	 {
325					{ 17, MAP_FAILED }, { 3, MAP_FAILED },
326					{ 11, MAP_FAILED }, { 2, MAP_FAILED },
327					{ 5, MAP_FAILED }, { 3, MAP_FAILED },
328					{ 7, MAP_FAILED }, { 1, MAP_FAILED },
329					{ 57, MAP_FAILED }, { 3, MAP_FAILED },
330					{ 131, MAP_FAILED }, { 1, MAP_FAILED },
331				};
332
333				for (m = 0; m < sizeof mm/sizeof(mm[0]); m++) {
334					HX(mm[m].p = mmap(NULL,
335					    mm[m].npg * pgs,
336					    PROT_READ|PROT_WRITE,
337					    MAP_PRIVATE|MAP_ANON, -1,
338					    (off_t)0), mm[m].p);
339					if (mm[m].p != MAP_FAILED) {
340						size_t mo;
341
342						/* Touch some memory... */
343						p = mm[m].p;
344						mo = cnt %
345						    (mm[m].npg * pgs - 1);
346						p[mo] = 1;
347						cnt += (int)((long)(mm[m].p)
348						    / pgs);
349					}
350
351					/* Check cnts and times... */
352					for (ii = 0; ii < sizeof(cl)/sizeof(cl[0]);
353					    ii++) {
354						HX((e = clock_gettime(cl[ii],
355						    &ts)) == -1, ts);
356						if (e != -1)
357							cnt += (int)ts.tv_nsec;
358					}
359
360					HX((e = getrusage(RUSAGE_SELF,
361					    &ru)) == -1, ru);
362					if (e != -1) {
363						cnt += (int)ru.ru_utime.tv_sec;
364						cnt += (int)ru.ru_utime.tv_usec;
365					}
366				}
367
368				for (m = 0; m < sizeof mm/sizeof(mm[0]); m++) {
369					if (mm[m].p != MAP_FAILED)
370						munmap(mm[m].p, mm[m].npg * pgs);
371					mm[m].p = MAP_FAILED;
372				}
373
374				HX(stat(".", &st) == -1, st);
375				HX(statvfs(".", &stvfs) == -1, stvfs);
376
377				HX(stat("/", &st) == -1, st);
378				HX(statvfs("/", &stvfs) == -1, stvfs);
379
380				HX((e = fstat(0, &st)) == -1, st);
381				if (e == -1) {
382					if (S_ISREG(st.st_mode) ||
383					    S_ISFIFO(st.st_mode) ||
384					    S_ISSOCK(st.st_mode)) {
385						HX(fstatvfs(0, &stvfs) == -1,
386						    stvfs);
387						HX((off = lseek(0, (off_t)0,
388						    SEEK_CUR)) < 0, off);
389					}
390					if (S_ISCHR(st.st_mode)) {
391						HX(tcgetattr(0, &tios) == -1,
392						    tios);
393					} else if (S_ISSOCK(st.st_mode)) {
394						memset(&ss, 0, sizeof ss);
395						ssl = sizeof(ss);
396						HX(getpeername(0,
397						    (void *)&ss, &ssl) == -1,
398						    ss);
399					}
400				}
401
402				HX((e = getrusage(RUSAGE_CHILDREN,
403				    &ru)) == -1, ru);
404				if (e != -1) {
405					cnt += (int)ru.ru_utime.tv_sec;
406					cnt += (int)ru.ru_utime.tv_usec;
407				}
408			} else {
409				/* Subsequent hashes absorb previous result */
410				HD(results);
411			}
412
413			HX((e = gettimeofday(&tv, NULL)) == -1, tv);
414			if (e != -1) {
415				cnt += (int)tv.tv_sec;
416				cnt += (int)tv.tv_usec;
417			}
418
419			HD(cnt);
420		}
421		SHA512_Final(results, &ctx);
422		memcpy((char *)buf + i, results, min(sizeof(results), len - i));
423		i += min(sizeof(results), len - i);
424	}
425	explicit_bzero(&ctx, sizeof ctx);
426	explicit_bzero(results, sizeof results);
427	errno = save_errno;
428	return (0);		/* satisfied */
429}
430