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1 | /* $OpenBSD: getentropy_osx.c,v 1.3 2014/07/12 14:48:00 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/sysctl.h> | |
27 | #include <sys/statvfs.h> | |
28 | #include <sys/socket.h> | |
29 | #include <sys/mount.h> | |
30 | #include <sys/mman.h> | |
31 | #include <sys/stat.h> | |
32 | #include <sys/time.h> | |
33 | #include <stdlib.h> | |
34 | #include <stdint.h> | |
35 | #include <stdio.h> | |
36 | #include <termios.h> | |
37 | #include <fcntl.h> | |
38 | #include <signal.h> | |
39 | #include <string.h> | |
40 | #include <errno.h> | |
41 | #include <unistd.h> | |
42 | #include <time.h> | |
43 | #include <mach/mach_time.h> | |
44 | #include <mach/mach_host.h> | |
45 | #include <mach/host_info.h> | |
46 | #include <sys/socketvar.h> | |
47 | #include <sys/vmmeter.h> | |
48 | #include <netinet/in.h> | |
49 | #include <netinet/tcp.h> | |
50 | #include <netinet/udp.h> | |
51 | #include <netinet/ip_var.h> | |
52 | #include <netinet/tcp_var.h> | |
53 | #include <netinet/udp_var.h> | |
54 | #include <CommonCrypto/CommonDigest.h> | |
55 | #define SHA512_Update(a, b, c) (CC_SHA512_Update((a), (b), (c))) | |
56 | #define SHA512_Init(xxx) (CC_SHA512_Init((xxx))) | |
57 | #define SHA512_Final(xxx, yyy) (CC_SHA512_Final((xxx), (yyy))) | |
58 | #define SHA512_CTX CC_SHA512_CTX | |
59 | #define SHA512_DIGEST_LENGTH CC_SHA512_DIGEST_LENGTH | |
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 | ||
76 | int getentropy(void *buf, size_t len); | |
77 | ||
78 | #ifdef CAN_REFERENCE_MAIN | |
79 | extern int main(int, char *argv[]); | |
80 | #endif | |
81 | static int gotdata(char *buf, size_t len); | |
82 | static int getentropy_urandom(void *buf, size_t len); | |
83 | static int getentropy_fallback(void *buf, size_t len); | |
84 | ||
85 | int | |
86 | getentropy(void *buf, size_t len) | |
87 | { | |
88 | int ret = -1; | |
89 | ||
90 | if (len > 256) { | |
91 | errno = EIO; | |
92 | return -1; | |
93 | } | |
94 | ||
95 | /* | |
96 | * Try to get entropy with /dev/urandom | |
97 | * | |
98 | * This can fail if the process is inside a chroot or if file | |
99 | * descriptors are exhausted. | |
100 | */ | |
101 | ret = getentropy_urandom(buf, len); | |
102 | if (ret != -1) | |
103 | return (ret); | |
104 | ||
105 | /* | |
106 | * Entropy collection via /dev/urandom and sysctl have failed. | |
107 | * | |
108 | * No other API exists for collecting entropy, and we have | |
109 | * no failsafe way to get it on OSX that is not sensitive | |
110 | * to resource exhaustion. | |
111 | * | |
112 | * We have very few options: | |
113 | * - Even syslog_r is unsafe to call at this low level, so | |
114 | * there is no way to alert the user or program. | |
115 | * - Cannot call abort() because some systems have unsafe | |
116 | * corefiles. | |
117 | * - Could raise(SIGKILL) resulting in silent program termination. | |
118 | * - Return EIO, to hint that arc4random's stir function | |
119 | * should raise(SIGKILL) | |
120 | * - Do the best under the circumstances.... | |
121 | * | |
122 | * This code path exists to bring light to the issue that OSX | |
123 | * does not provide a failsafe API for entropy collection. | |
124 | * | |
125 | * We hope this demonstrates that OSX should consider | |
126 | * providing a new failsafe API which works in a chroot or | |
127 | * when file descriptors are exhausted. | |
128 | */ | |
129 | #undef FAIL_INSTEAD_OF_TRYING_FALLBACK | |
130 | #ifdef FAIL_INSTEAD_OF_TRYING_FALLBACK | |
131 | raise(SIGKILL); | |
132 | #endif | |
133 | ret = getentropy_fallback(buf, len); | |
134 | if (ret != -1) | |
135 | return (ret); | |
136 | ||
137 | errno = EIO; | |
138 | return (ret); | |
139 | } | |
140 | ||
141 | /* | |
142 | * Basic sanity checking; wish we could do better. | |
143 | */ | |
144 | static int | |
145 | gotdata(char *buf, size_t len) | |
146 | { | |
147 | char any_set = 0; | |
148 | size_t i; | |
149 | ||
150 | for (i = 0; i < len; ++i) | |
151 | any_set |= buf[i]; | |
152 | if (any_set == 0) | |
153 | return -1; | |
154 | return 0; | |
155 | } | |
156 | ||
157 | static int | |
158 | getentropy_urandom(void *buf, size_t len) | |
159 | { | |
160 | struct stat st; | |
161 | size_t i; | |
162 | int fd, flags; | |
163 | int save_errno = errno; | |
164 | ||
165 | start: | |
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("/dev/urandom", 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 | close(fd); | |
187 | goto nodevrandom; | |
188 | } | |
189 | for (i = 0; i < len; ) { | |
190 | size_t wanted = len - i; | |
191 | ssize_t ret = read(fd, (char*)buf + i, wanted); | |
192 | ||
193 | if (ret == -1) { | |
194 | if (errno == EAGAIN || errno == EINTR) | |
195 | continue; | |
196 | close(fd); | |
197 | goto nodevrandom; | |
198 | } | |
199 | i += ret; | |
200 | } | |
201 | close(fd); | |
202 | if (gotdata(buf, len) == 0) { | |
203 | errno = save_errno; | |
204 | return 0; /* satisfied */ | |
205 | } | |
206 | nodevrandom: | |
207 | errno = EIO; | |
208 | return -1; | |
209 | } | |
210 | ||
211 | static int tcpmib[] = { CTL_NET, AF_INET, IPPROTO_TCP, TCPCTL_STATS }; | |
212 | static int udpmib[] = { CTL_NET, AF_INET, IPPROTO_UDP, UDPCTL_STATS }; | |
213 | static int ipmib[] = { CTL_NET, AF_INET, IPPROTO_IP, IPCTL_STATS }; | |
214 | static int kmib[] = { CTL_KERN, KERN_USRSTACK }; | |
215 | static int hwmib[] = { CTL_HW, HW_USERMEM }; | |
216 | ||
217 | static int | |
218 | getentropy_fallback(void *buf, size_t len) | |
219 | { | |
220 | uint8_t results[SHA512_DIGEST_LENGTH]; | |
221 | int save_errno = errno, e, pgs = getpagesize(), faster = 0, repeat; | |
222 | static int cnt; | |
223 | struct timespec ts; | |
224 | struct timeval tv; | |
225 | struct rusage ru; | |
226 | sigset_t sigset; | |
227 | struct stat st; | |
228 | SHA512_CTX ctx; | |
229 | static pid_t lastpid; | |
230 | pid_t pid; | |
231 | size_t i, ii, m; | |
232 | char *p; | |
233 | struct tcpstat tcpstat; | |
234 | struct udpstat udpstat; | |
235 | struct ipstat ipstat; | |
236 | u_int64_t mach_time; | |
237 | unsigned int idata; | |
238 | void *addr; | |
239 | ||
240 | pid = getpid(); | |
241 | if (lastpid == pid) { | |
242 | faster = 1; | |
243 | repeat = 2; | |
244 | } else { | |
245 | faster = 0; | |
246 | lastpid = pid; | |
247 | repeat = REPEAT; | |
248 | } | |
249 | for (i = 0; i < len; ) { | |
250 | int j; | |
251 | SHA512_Init(&ctx); | |
252 | for (j = 0; j < repeat; j++) { | |
253 | HX((e = gettimeofday(&tv, NULL)) == -1, tv); | |
254 | if (e != -1) { | |
255 | cnt += (int)tv.tv_sec; | |
256 | cnt += (int)tv.tv_usec; | |
257 | } | |
258 | ||
259 | mach_time = mach_absolute_time(); | |
260 | HD(mach_time); | |
261 | ||
262 | ii = sizeof(addr); | |
263 | HX(sysctl(kmib, sizeof(kmib) / sizeof(kmib[0]), | |
264 | &addr, &ii, NULL, 0) == -1, addr); | |
265 | ||
266 | ii = sizeof(idata); | |
267 | HX(sysctl(hwmib, sizeof(hwmib) / sizeof(hwmib[0]), | |
268 | &idata, &ii, NULL, 0) == -1, idata); | |
269 | ||
270 | ii = sizeof(tcpstat); | |
271 | HX(sysctl(tcpmib, sizeof(tcpmib) / sizeof(tcpmib[0]), | |
272 | &tcpstat, &ii, NULL, 0) == -1, tcpstat); | |
273 | ||
274 | ii = sizeof(udpstat); | |
275 | HX(sysctl(udpmib, sizeof(udpmib) / sizeof(udpmib[0]), | |
276 | &udpstat, &ii, NULL, 0) == -1, udpstat); | |
277 | ||
278 | ii = sizeof(ipstat); | |
279 | HX(sysctl(ipmib, sizeof(ipmib) / sizeof(ipmib[0]), | |
280 | &ipstat, &ii, NULL, 0) == -1, ipstat); | |
281 | ||
282 | HX((pid = getpid()) == -1, pid); | |
283 | HX((pid = getsid(pid)) == -1, pid); | |
284 | HX((pid = getppid()) == -1, pid); | |
285 | HX((pid = getpgid(0)) == -1, pid); | |
286 | HX((e = getpriority(0, 0)) == -1, e); | |
287 | ||
288 | if (!faster) { | |
289 | ts.tv_sec = 0; | |
290 | ts.tv_nsec = 1; | |
291 | (void) nanosleep(&ts, NULL); | |
292 | } | |
293 | ||
294 | HX(sigpending(&sigset) == -1, sigset); | |
295 | HX(sigprocmask(SIG_BLOCK, NULL, &sigset) == -1, | |
296 | sigset); | |
297 | ||
298 | #ifdef CAN_REFERENCE_MAIN | |
299 | HF(main); /* an addr in program */ | |
300 | #endif | |
301 | HF(getentropy); /* an addr in this library */ | |
302 | HF(printf); /* an addr in libc */ | |
303 | p = (char *)&p; | |
304 | HD(p); /* an addr on stack */ | |
305 | p = (char *)&errno; | |
306 | HD(p); /* the addr of errno */ | |
307 | ||
308 | if (i == 0) { | |
309 | struct sockaddr_storage ss; | |
310 | struct statvfs stvfs; | |
311 | struct termios tios; | |
312 | struct statfs stfs; | |
313 | socklen_t ssl; | |
314 | off_t off; | |
315 | ||
316 | /* | |
317 | * Prime-sized mappings encourage fragmentation; | |
318 | * thus exposing some address entropy. | |
319 | */ | |
320 | struct mm { | |
321 | size_t npg; | |
322 | void *p; | |
323 | } mm[] = { | |
324 | { 17, MAP_FAILED }, { 3, MAP_FAILED }, | |
325 | { 11, MAP_FAILED }, { 2, MAP_FAILED }, | |
326 | { 5, MAP_FAILED }, { 3, MAP_FAILED }, | |
327 | { 7, MAP_FAILED }, { 1, MAP_FAILED }, | |
328 | { 57, MAP_FAILED }, { 3, MAP_FAILED }, | |
329 | { 131, MAP_FAILED }, { 1, MAP_FAILED }, | |
330 | }; | |
331 | ||
332 | for (m = 0; m < sizeof mm/sizeof(mm[0]); m++) { | |
333 | HX(mm[m].p = mmap(NULL, | |
334 | mm[m].npg * pgs, | |
335 | PROT_READ|PROT_WRITE, | |
336 | MAP_PRIVATE|MAP_ANON, -1, | |
337 | (off_t)0), mm[m].p); | |
338 | if (mm[m].p != MAP_FAILED) { | |
339 | size_t mo; | |
340 | ||
341 | /* Touch some memory... */ | |
342 | p = mm[m].p; | |
343 | mo = cnt % | |
344 | (mm[m].npg * pgs - 1); | |
345 | p[mo] = 1; | |
346 | cnt += (int)((long)(mm[m].p) | |
347 | / pgs); | |
348 | } | |
349 | ||
350 | /* Check cnts and times... */ | |
351 | mach_time = mach_absolute_time(); | |
352 | HD(mach_time); | |
353 | cnt += (int)mach_time; | |
354 | ||
355 | HX((e = getrusage(RUSAGE_SELF, | |
356 | &ru)) == -1, ru); | |
357 | if (e != -1) { | |
358 | cnt += (int)ru.ru_utime.tv_sec; | |
359 | cnt += (int)ru.ru_utime.tv_usec; | |
360 | } | |
361 | } | |
362 | ||
363 | for (m = 0; m < sizeof mm/sizeof(mm[0]); m++) { | |
364 | if (mm[m].p != MAP_FAILED) | |
365 | munmap(mm[m].p, mm[m].npg * pgs); | |
366 | mm[m].p = MAP_FAILED; | |
367 | } | |
368 | ||
369 | HX(stat(".", &st) == -1, st); | |
370 | HX(statvfs(".", &stvfs) == -1, stvfs); | |
371 | HX(statfs(".", &stfs) == -1, stfs); | |
372 | ||
373 | HX(stat("/", &st) == -1, st); | |
374 | HX(statvfs("/", &stvfs) == -1, stvfs); | |
375 | HX(statfs("/", &stfs) == -1, stfs); | |
376 | ||
377 | HX((e = fstat(0, &st)) == -1, st); | |
378 | if (e == -1) { | |
379 | if (S_ISREG(st.st_mode) || | |
380 | S_ISFIFO(st.st_mode) || | |
381 | S_ISSOCK(st.st_mode)) { | |
382 | HX(fstatvfs(0, &stvfs) == -1, | |
383 | stvfs); | |
384 | HX(fstatfs(0, &stfs) == -1, | |
385 | stfs); | |
386 | HX((off = lseek(0, (off_t)0, | |
387 | SEEK_CUR)) < 0, off); | |
388 | } | |
389 | if (S_ISCHR(st.st_mode)) { | |
390 | HX(tcgetattr(0, &tios) == -1, | |
391 | tios); | |
392 | } else if (S_ISSOCK(st.st_mode)) { | |
393 | memset(&ss, 0, sizeof ss); | |
394 | ssl = sizeof(ss); | |
395 | HX(getpeername(0, | |
396 | (void *)&ss, &ssl) == -1, | |
397 | ss); | |
398 | } | |
399 | } | |
400 | ||
401 | HX((e = getrusage(RUSAGE_CHILDREN, | |
402 | &ru)) == -1, ru); | |
403 | if (e != -1) { | |
404 | cnt += (int)ru.ru_utime.tv_sec; | |
405 | cnt += (int)ru.ru_utime.tv_usec; | |
406 | } | |
407 | } else { | |
408 | /* Subsequent hashes absorb previous result */ | |
409 | HD(results); | |
410 | } | |
411 | ||
412 | HX((e = gettimeofday(&tv, NULL)) == -1, tv); | |
413 | if (e != -1) { | |
414 | cnt += (int)tv.tv_sec; | |
415 | cnt += (int)tv.tv_usec; | |
416 | } | |
417 | ||
418 | HD(cnt); | |
419 | } | |
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 | memset(results, 0, sizeof results); | |
426 | if (gotdata(buf, len) == 0) { | |
427 | errno = save_errno; | |
428 | return 0; /* satisfied */ | |
429 | } | |
430 | errno = EIO; | |
431 | return -1; | |
432 | } |