1 /* $OpenBSD: getentropy_osx.c,v 1.13 2020/05/17 14:44:20 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 #include <TargetConditionals.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/sysctl.h>
30 #include <sys/statvfs.h>
31 #include <sys/socket.h>
32 #include <sys/mount.h>
33 #include <sys/mman.h>
34 #include <sys/stat.h>
35 #include <sys/time.h>
36 #include <stdlib.h>
37 #include <stdint.h>
38 #include <stdio.h>
39 #include <termios.h>
40 #include <fcntl.h>
41 #include <signal.h>
42 #include <string.h>
43 #include <errno.h>
44 #include <unistd.h>
45 #include <time.h>
46 #include <mach/mach_time.h>
47 #include <mach/mach_host.h>
48 #include <mach/host_info.h>
49 #if TARGET_OS_OSX
50 #include <sys/socketvar.h>
51 #include <sys/vmmeter.h>
52 #endif
53 #include <netinet/in.h>
54 #include <netinet/tcp.h>
55 #if TARGET_OS_OSX
56 #include <netinet/udp.h>
57 #include <netinet/ip_var.h>
58 #include <netinet/tcp_var.h>
59 #include <netinet/udp_var.h>
60 #endif
61 #include <CommonCrypto/CommonDigest.h>
62 #define SHA512_Update(a, b, c) (CC_SHA512_Update((a), (b), (c)))
63 #define SHA512_Init(xxx) (CC_SHA512_Init((xxx)))
64 #define SHA512_Final(xxx, yyy) (CC_SHA512_Final((xxx), (yyy)))
65 #define SHA512_CTX CC_SHA512_CTX
66 #define SHA512_DIGEST_LENGTH CC_SHA512_DIGEST_LENGTH
67
68 #define REPEAT 5
69 #define MINIMUM(a, b) (((a) < (b)) ? (a) : (b))
70
71 #define HX(a, b) \
72 do { \
73 if ((a)) \
74 HD(errno); \
75 else \
76 HD(b); \
77 } while (0)
78
79 #define HR(x, l) (SHA512_Update(&ctx, (char *)(x), (l)))
80 #define HD(x) (SHA512_Update(&ctx, (char *)&(x), sizeof (x)))
81 #define HF(x) (SHA512_Update(&ctx, (char *)&(x), sizeof (void*)))
82
83 int getentropy(void *buf, size_t len);
84
85 static int getentropy_urandom(void *buf, size_t len);
86 static int getentropy_fallback(void *buf, size_t len);
87
88 int
getentropy(void * buf,size_t len)89 getentropy(void *buf, size_t len)
90 {
91 int ret = -1;
92
93 if (len > 256) {
94 errno = EIO;
95 return (-1);
96 }
97
98 /*
99 * Try to get entropy with /dev/urandom
100 *
101 * This can fail if the process is inside a chroot or if file
102 * descriptors are exhausted.
103 */
104 ret = getentropy_urandom(buf, len);
105 if (ret != -1)
106 return (ret);
107
108 /*
109 * Entropy collection via /dev/urandom and sysctl have failed.
110 *
111 * No other API exists for collecting entropy, and we have
112 * no failsafe way to get it on OSX that is not sensitive
113 * to resource exhaustion.
114 *
115 * We have very few options:
116 * - Even syslog_r is unsafe to call at this low level, so
117 * there is no way to alert the user or program.
118 * - Cannot call abort() because some systems have unsafe
119 * corefiles.
120 * - Could raise(SIGKILL) resulting in silent program termination.
121 * - Return EIO, to hint that arc4random's stir function
122 * should raise(SIGKILL)
123 * - Do the best under the circumstances....
124 *
125 * This code path exists to bring light to the issue that OSX
126 * does not provide a failsafe API for entropy collection.
127 *
128 * We hope this demonstrates that OSX should consider
129 * providing a new failsafe API which works in a chroot or
130 * when file descriptors are exhausted.
131 */
132 #undef FAIL_INSTEAD_OF_TRYING_FALLBACK
133 #ifdef FAIL_INSTEAD_OF_TRYING_FALLBACK
134 raise(SIGKILL);
135 #endif
136 ret = getentropy_fallback(buf, len);
137 if (ret != -1)
138 return (ret);
139
140 errno = EIO;
141 return (ret);
142 }
143
144 static int
getentropy_urandom(void * buf,size_t len)145 getentropy_urandom(void *buf, size_t len)
146 {
147 struct stat st;
148 size_t i;
149 int fd, flags;
150 int save_errno = errno;
151
152 start:
153
154 flags = O_RDONLY;
155 #ifdef O_NOFOLLOW
156 flags |= O_NOFOLLOW;
157 #endif
158 #ifdef O_CLOEXEC
159 flags |= O_CLOEXEC;
160 #endif
161 fd = open("/dev/urandom", flags, 0);
162 if (fd == -1) {
163 if (errno == EINTR)
164 goto start;
165 goto nodevrandom;
166 }
167 #ifndef O_CLOEXEC
168 fcntl(fd, F_SETFD, fcntl(fd, F_GETFD) | FD_CLOEXEC);
169 #endif
170
171 /* Lightly verify that the device node looks sane */
172 if (fstat(fd, &st) == -1 || !S_ISCHR(st.st_mode)) {
173 close(fd);
174 goto nodevrandom;
175 }
176 for (i = 0; i < len; ) {
177 size_t wanted = len - i;
178 ssize_t ret = read(fd, (char *)buf + i, wanted);
179
180 if (ret == -1) {
181 if (errno == EAGAIN || errno == EINTR)
182 continue;
183 close(fd);
184 goto nodevrandom;
185 }
186 i += ret;
187 }
188 close(fd);
189 errno = save_errno;
190 return (0); /* satisfied */
191 nodevrandom:
192 errno = EIO;
193 return (-1);
194 }
195
196 #if TARGET_OS_OSX
197 static int tcpmib[] = { CTL_NET, AF_INET, IPPROTO_TCP, TCPCTL_STATS };
198 static int udpmib[] = { CTL_NET, AF_INET, IPPROTO_UDP, UDPCTL_STATS };
199 static int ipmib[] = { CTL_NET, AF_INET, IPPROTO_IP, IPCTL_STATS };
200 #endif
201 static int kmib[] = { CTL_KERN, KERN_USRSTACK };
202 static int hwmib[] = { CTL_HW, HW_USERMEM };
203
204 static int
getentropy_fallback(void * buf,size_t len)205 getentropy_fallback(void *buf, size_t len)
206 {
207 uint8_t results[SHA512_DIGEST_LENGTH];
208 int save_errno = errno, e, pgs = getpagesize(), faster = 0, repeat;
209 static int cnt;
210 struct timespec ts;
211 struct timeval tv;
212 struct rusage ru;
213 sigset_t sigset;
214 struct stat st;
215 SHA512_CTX ctx;
216 static pid_t lastpid;
217 pid_t pid;
218 size_t i, ii, m;
219 char *p;
220 #if TARGET_OS_OSX
221 struct tcpstat tcpstat;
222 struct udpstat udpstat;
223 struct ipstat ipstat;
224 #endif
225 u_int64_t mach_time;
226 unsigned int idata;
227 void *addr;
228
229 pid = getpid();
230 if (lastpid == pid) {
231 faster = 1;
232 repeat = 2;
233 } else {
234 faster = 0;
235 lastpid = pid;
236 repeat = REPEAT;
237 }
238 for (i = 0; i < len; ) {
239 int j;
240 SHA512_Init(&ctx);
241 for (j = 0; j < repeat; j++) {
242 HX((e = gettimeofday(&tv, NULL)) == -1, tv);
243 if (e != -1) {
244 cnt += (int)tv.tv_sec;
245 cnt += (int)tv.tv_usec;
246 }
247
248 mach_time = mach_absolute_time();
249 HD(mach_time);
250
251 ii = sizeof(addr);
252 HX(sysctl(kmib, sizeof(kmib) / sizeof(kmib[0]),
253 &addr, &ii, NULL, 0) == -1, addr);
254
255 ii = sizeof(idata);
256 HX(sysctl(hwmib, sizeof(hwmib) / sizeof(hwmib[0]),
257 &idata, &ii, NULL, 0) == -1, idata);
258
259 #if TARGET_OS_OSX
260 ii = sizeof(tcpstat);
261 HX(sysctl(tcpmib, sizeof(tcpmib) / sizeof(tcpmib[0]),
262 &tcpstat, &ii, NULL, 0) == -1, tcpstat);
263
264 ii = sizeof(udpstat);
265 HX(sysctl(udpmib, sizeof(udpmib) / sizeof(udpmib[0]),
266 &udpstat, &ii, NULL, 0) == -1, udpstat);
267
268 ii = sizeof(ipstat);
269 HX(sysctl(ipmib, sizeof(ipmib) / sizeof(ipmib[0]),
270 &ipstat, &ii, NULL, 0) == -1, ipstat);
271 #endif
272
273 HX((pid = getpid()) == -1, pid);
274 HX((pid = getsid(pid)) == -1, pid);
275 HX((pid = getppid()) == -1, pid);
276 HX((pid = getpgid(0)) == -1, pid);
277 HX((e = getpriority(0, 0)) == -1, e);
278
279 if (!faster) {
280 ts.tv_sec = 0;
281 ts.tv_nsec = 1;
282 (void) nanosleep(&ts, NULL);
283 }
284
285 HX(sigpending(&sigset) == -1, sigset);
286 HX(sigprocmask(SIG_BLOCK, NULL, &sigset) == -1,
287 sigset);
288
289 HF(getentropy); /* an addr in this library */
290 HF(printf); /* an addr in libc */
291 p = (char *)&p;
292 HD(p); /* an addr on stack */
293 p = (char *)&errno;
294 HD(p); /* the addr of errno */
295
296 if (i == 0) {
297 struct sockaddr_storage ss;
298 struct statvfs stvfs;
299 struct termios tios;
300 struct statfs stfs;
301 socklen_t ssl;
302 off_t off;
303
304 /*
305 * Prime-sized mappings encourage fragmentation;
306 * thus exposing some address entropy.
307 */
308 struct mm {
309 size_t npg;
310 void *p;
311 } mm[] = {
312 { 17, MAP_FAILED }, { 3, MAP_FAILED },
313 { 11, MAP_FAILED }, { 2, MAP_FAILED },
314 { 5, MAP_FAILED }, { 3, MAP_FAILED },
315 { 7, MAP_FAILED }, { 1, MAP_FAILED },
316 { 57, MAP_FAILED }, { 3, MAP_FAILED },
317 { 131, MAP_FAILED }, { 1, MAP_FAILED },
318 };
319
320 for (m = 0; m < sizeof mm/sizeof(mm[0]); m++) {
321 HX(mm[m].p = mmap(NULL,
322 mm[m].npg * pgs,
323 PROT_READ|PROT_WRITE,
324 MAP_PRIVATE|MAP_ANON, -1,
325 (off_t)0), mm[m].p);
326 if (mm[m].p != MAP_FAILED) {
327 size_t mo;
328
329 /* Touch some memory... */
330 p = mm[m].p;
331 mo = cnt %
332 (mm[m].npg * pgs - 1);
333 p[mo] = 1;
334 cnt += (int)((long)(mm[m].p)
335 / pgs);
336 }
337
338 /* Check cnts and times... */
339 mach_time = mach_absolute_time();
340 HD(mach_time);
341 cnt += (int)mach_time;
342
343 HX((e = getrusage(RUSAGE_SELF,
344 &ru)) == -1, ru);
345 if (e != -1) {
346 cnt += (int)ru.ru_utime.tv_sec;
347 cnt += (int)ru.ru_utime.tv_usec;
348 }
349 }
350
351 for (m = 0; m < sizeof mm/sizeof(mm[0]); m++) {
352 if (mm[m].p != MAP_FAILED)
353 munmap(mm[m].p, mm[m].npg * pgs);
354 mm[m].p = MAP_FAILED;
355 }
356
357 HX(stat(".", &st) == -1, st);
358 HX(statvfs(".", &stvfs) == -1, stvfs);
359 HX(statfs(".", &stfs) == -1, stfs);
360
361 HX(stat("/", &st) == -1, st);
362 HX(statvfs("/", &stvfs) == -1, stvfs);
363 HX(statfs("/", &stfs) == -1, stfs);
364
365 HX((e = fstat(0, &st)) == -1, st);
366 if (e == -1) {
367 if (S_ISREG(st.st_mode) ||
368 S_ISFIFO(st.st_mode) ||
369 S_ISSOCK(st.st_mode)) {
370 HX(fstatvfs(0, &stvfs) == -1,
371 stvfs);
372 HX(fstatfs(0, &stfs) == -1,
373 stfs);
374 HX((off = lseek(0, (off_t)0,
375 SEEK_CUR)) < 0, off);
376 }
377 if (S_ISCHR(st.st_mode)) {
378 HX(tcgetattr(0, &tios) == -1,
379 tios);
380 } else if (S_ISSOCK(st.st_mode)) {
381 memset(&ss, 0, sizeof ss);
382 ssl = sizeof(ss);
383 HX(getpeername(0,
384 (void *)&ss, &ssl) == -1,
385 ss);
386 }
387 }
388
389 HX((e = getrusage(RUSAGE_CHILDREN,
390 &ru)) == -1, ru);
391 if (e != -1) {
392 cnt += (int)ru.ru_utime.tv_sec;
393 cnt += (int)ru.ru_utime.tv_usec;
394 }
395 } else {
396 /* Subsequent hashes absorb previous result */
397 HD(results);
398 }
399
400 HX((e = gettimeofday(&tv, NULL)) == -1, tv);
401 if (e != -1) {
402 cnt += (int)tv.tv_sec;
403 cnt += (int)tv.tv_usec;
404 }
405
406 HD(cnt);
407 }
408
409 SHA512_Final(results, &ctx);
410 memcpy((char *)buf + i, results, MINIMUM(sizeof(results), len - i));
411 i += MINIMUM(sizeof(results), len - i);
412 }
413 explicit_bzero(&ctx, sizeof ctx);
414 explicit_bzero(results, sizeof results);
415 errno = save_errno;
416 return (0); /* satisfied */
417 }
418