lua-arc4random

Cryptographically secure PRNG for Lua
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getentropy_linux.c (12915B)


      1 /*	$OpenBSD: getentropy_linux.c,v 1.35 2014/08/28 01:00:57 bcook 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 #include <openssl/sha.h>
     51 
     52 #include <linux/types.h>
     53 #include <linux/random.h>
     54 #include <linux/sysctl.h>
     55 #ifdef HAVE_GETAUXVAL
     56 #include <sys/auxv.h>
     57 #endif
     58 #include <sys/vfs.h>
     59 
     60 #define REPEAT 5
     61 #define min(a, b) (((a) < (b)) ? (a) : (b))
     62 
     63 #define HX(a, b) \
     64 	do { \
     65 		if ((a)) \
     66 			HD(errno); \
     67 		else \
     68 			HD(b); \
     69 	} while (0)
     70 
     71 #define HR(x, l) (SHA512_Update(&ctx, (char *)(x), (l)))
     72 #define HD(x)	 (SHA512_Update(&ctx, (char *)&(x), sizeof (x)))
     73 #define HF(x)    (SHA512_Update(&ctx, (char *)&(x), sizeof (void*)))
     74 
     75 int	getentropy(void *buf, size_t len);
     76 
     77 static int gotdata(char *buf, size_t len);
     78 #ifdef SYS_getrandom
     79 static int getentropy_getrandom(void *buf, size_t len);
     80 #endif
     81 static int getentropy_urandom(void *buf, size_t len);
     82 #ifdef SYS__sysctl
     83 static int getentropy_sysctl(void *buf, size_t len);
     84 #endif
     85 static int getentropy_fallback(void *buf, size_t len);
     86 static int getentropy_phdr(struct dl_phdr_info *info, size_t size, void *data);
     87 
     88 int
     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 #ifdef SYS_getrandom
     99 	/*
    100 	 * Try descriptor-less getrandom()
    101 	 */
    102 	ret = getentropy_getrandom(buf, len);
    103 	if (ret != -1)
    104 		return (ret);
    105 	if (errno != ENOSYS)
    106 		return (-1);
    107 #endif
    108 
    109 	/*
    110 	 * Try to get entropy with /dev/urandom
    111 	 *
    112 	 * This can fail if the process is inside a chroot or if file
    113 	 * descriptors are exhausted.
    114 	 */
    115 	ret = getentropy_urandom(buf, len);
    116 	if (ret != -1)
    117 		return (ret);
    118 
    119 #ifdef SYS__sysctl
    120 	/*
    121 	 * Try to use sysctl CTL_KERN, KERN_RANDOM, RANDOM_UUID.
    122 	 * sysctl is a failsafe API, so it guarantees a result.  This
    123 	 * should work inside a chroot, or when file descriptors are
    124 	 * exhuasted.
    125 	 *
    126 	 * However this can fail if the Linux kernel removes support
    127 	 * for sysctl.  Starting in 2007, there have been efforts to
    128 	 * deprecate the sysctl API/ABI, and push callers towards use
    129 	 * of the chroot-unavailable fd-using /proc mechanism --
    130 	 * essentially the same problems as /dev/urandom.
    131 	 *
    132 	 * Numerous setbacks have been encountered in their deprecation
    133 	 * schedule, so as of June 2014 the kernel ABI still exists on
    134 	 * most Linux architectures. The sysctl() stub in libc is missing
    135 	 * on some systems.  There are also reports that some kernels
    136 	 * spew messages to the console.
    137 	 */
    138 	ret = getentropy_sysctl(buf, len);
    139 	if (ret != -1)
    140 		return (ret);
    141 #endif /* SYS__sysctl */
    142 
    143 	/*
    144 	 * Entropy collection via /dev/urandom and sysctl have failed.
    145 	 *
    146 	 * No other API exists for collecting entropy.  See the large
    147 	 * comment block above.
    148 	 *
    149 	 * We have very few options:
    150 	 *     - Even syslog_r is unsafe to call at this low level, so
    151 	 *	 there is no way to alert the user or program.
    152 	 *     - Cannot call abort() because some systems have unsafe
    153 	 *	 corefiles.
    154 	 *     - Could raise(SIGKILL) resulting in silent program termination.
    155 	 *     - Return EIO, to hint that arc4random's stir function
    156 	 *       should raise(SIGKILL)
    157 	 *     - Do the best under the circumstances....
    158 	 *
    159 	 * This code path exists to bring light to the issue that Linux
    160 	 * does not provide a failsafe API for entropy collection.
    161 	 *
    162 	 * We hope this demonstrates that Linux should either retain their
    163 	 * sysctl ABI, or consider providing a new failsafe API which
    164 	 * works in a chroot or when file descriptors are exhausted.
    165 	 */
    166 #undef FAIL_INSTEAD_OF_TRYING_FALLBACK
    167 #ifdef FAIL_INSTEAD_OF_TRYING_FALLBACK
    168 	raise(SIGKILL);
    169 #endif
    170 	ret = getentropy_fallback(buf, len);
    171 	if (ret != -1)
    172 		return (ret);
    173 
    174 	errno = EIO;
    175 	return (ret);
    176 }
    177 
    178 /*
    179  * Basic sanity checking; wish we could do better.
    180  */
    181 static int
    182 gotdata(char *buf, size_t len)
    183 {
    184 	char	any_set = 0;
    185 	size_t	i;
    186 
    187 	for (i = 0; i < len; ++i)
    188 		any_set |= buf[i];
    189 	if (any_set == 0)
    190 		return -1;
    191 	return 0;
    192 }
    193 
    194 #ifdef SYS_getrandom
    195 static int
    196 getentropy_getrandom(void *buf, size_t len)
    197 {
    198 	int pre_errno = errno;
    199 	int ret;
    200 	if (len > 256)
    201 		return (-1);
    202 	do {
    203 		ret = syscall(SYS_getrandom, buf, len, 0);
    204 	} while (ret == -1 && errno == EINTR);
    205 
    206 	if (ret != len)
    207 		return (-1);
    208 	errno = pre_errno;
    209 	return (0);
    210 }
    211 #endif
    212 
    213 static int
    214 getentropy_urandom(void *buf, size_t len)
    215 {
    216 	struct stat st;
    217 	size_t i;
    218 	int fd, cnt, flags;
    219 	int save_errno = errno;
    220 
    221 start:
    222 
    223 	flags = O_RDONLY;
    224 #ifdef O_NOFOLLOW
    225 	flags |= O_NOFOLLOW;
    226 #endif
    227 #ifdef O_CLOEXEC
    228 	flags |= O_CLOEXEC;
    229 #endif
    230 	fd = open("/dev/urandom", flags, 0);
    231 	if (fd == -1) {
    232 		if (errno == EINTR)
    233 			goto start;
    234 		goto nodevrandom;
    235 	}
    236 #ifndef O_CLOEXEC
    237 	fcntl(fd, F_SETFD, fcntl(fd, F_GETFD) | FD_CLOEXEC);
    238 #endif
    239 
    240 	/* Lightly verify that the device node looks sane */
    241 	if (fstat(fd, &st) == -1 || !S_ISCHR(st.st_mode)) {
    242 		close(fd);
    243 		goto nodevrandom;
    244 	}
    245 	if (ioctl(fd, RNDGETENTCNT, &cnt) == -1) {
    246 		close(fd);
    247 		goto nodevrandom;
    248 	}
    249 	for (i = 0; i < len; ) {
    250 		size_t wanted = len - i;
    251 		ssize_t ret = read(fd, (char *)buf + i, wanted);
    252 
    253 		if (ret == -1) {
    254 			if (errno == EAGAIN || errno == EINTR)
    255 				continue;
    256 			close(fd);
    257 			goto nodevrandom;
    258 		}
    259 		i += ret;
    260 	}
    261 	close(fd);
    262 	if (gotdata(buf, len) == 0) {
    263 		errno = save_errno;
    264 		return 0;		/* satisfied */
    265 	}
    266 nodevrandom:
    267 	errno = EIO;
    268 	return -1;
    269 }
    270 
    271 #ifdef SYS__sysctl
    272 static int
    273 getentropy_sysctl(void *buf, size_t len)
    274 {
    275 	static int mib[] = { CTL_KERN, KERN_RANDOM, RANDOM_UUID };
    276 	size_t i;
    277 	int save_errno = errno;
    278 
    279 	for (i = 0; i < len; ) {
    280 		size_t chunk = min(len - i, 16);
    281 
    282 		/* SYS__sysctl because some systems already removed sysctl() */
    283 		struct __sysctl_args args = {
    284 			.name = mib,
    285 			.nlen = 3,
    286 			.oldval = (char *)buf + i,
    287 			.oldlenp = &chunk,
    288 		};
    289 		if (syscall(SYS__sysctl, &args) != 0)
    290 			goto sysctlfailed;
    291 		i += chunk;
    292 	}
    293 	if (gotdata(buf, len) == 0) {
    294 		errno = save_errno;
    295 		return (0);			/* satisfied */
    296 	}
    297 sysctlfailed:
    298 	errno = EIO;
    299 	return -1;
    300 }
    301 #endif /* SYS__sysctl */
    302 
    303 static int cl[] = {
    304 	CLOCK_REALTIME,
    305 #ifdef CLOCK_MONOTONIC
    306 	CLOCK_MONOTONIC,
    307 #endif
    308 #ifdef CLOCK_MONOTONIC_RAW
    309 	CLOCK_MONOTONIC_RAW,
    310 #endif
    311 #ifdef CLOCK_TAI
    312 	CLOCK_TAI,
    313 #endif
    314 #ifdef CLOCK_VIRTUAL
    315 	CLOCK_VIRTUAL,
    316 #endif
    317 #ifdef CLOCK_UPTIME
    318 	CLOCK_UPTIME,
    319 #endif
    320 #ifdef CLOCK_PROCESS_CPUTIME_ID
    321 	CLOCK_PROCESS_CPUTIME_ID,
    322 #endif
    323 #ifdef CLOCK_THREAD_CPUTIME_ID
    324 	CLOCK_THREAD_CPUTIME_ID,
    325 #endif
    326 };
    327 
    328 static int
    329 getentropy_phdr(struct dl_phdr_info *info, size_t size, void *data)
    330 {
    331 	SHA512_CTX *ctx = data;
    332 
    333 	SHA512_Update(ctx, &info->dlpi_addr, sizeof (info->dlpi_addr));
    334 	return 0;
    335 }
    336 
    337 static int
    338 getentropy_fallback(void *buf, size_t len)
    339 {
    340 	uint8_t results[SHA512_DIGEST_LENGTH];
    341 	int save_errno = errno, e, pgs = getpagesize(), faster = 0, repeat;
    342 	static int cnt;
    343 	struct timespec ts;
    344 	struct timeval tv;
    345 	struct rusage ru;
    346 	sigset_t sigset;
    347 	struct stat st;
    348 	SHA512_CTX ctx;
    349 	static pid_t lastpid;
    350 	pid_t pid;
    351 	size_t i, ii, m;
    352 	char *p;
    353 
    354 	pid = getpid();
    355 	if (lastpid == pid) {
    356 		faster = 1;
    357 		repeat = 2;
    358 	} else {
    359 		faster = 0;
    360 		lastpid = pid;
    361 		repeat = REPEAT;
    362 	}
    363 	for (i = 0; i < len; ) {
    364 		int j;
    365 		SHA512_Init(&ctx);
    366 		for (j = 0; j < repeat; j++) {
    367 			HX((e = gettimeofday(&tv, NULL)) == -1, tv);
    368 			if (e != -1) {
    369 				cnt += (int)tv.tv_sec;
    370 				cnt += (int)tv.tv_usec;
    371 			}
    372 
    373 			dl_iterate_phdr(getentropy_phdr, &ctx);
    374 
    375 			for (ii = 0; ii < sizeof(cl)/sizeof(cl[0]); ii++)
    376 				HX(clock_gettime(cl[ii], &ts) == -1, ts);
    377 
    378 			HX((pid = getpid()) == -1, pid);
    379 			HX((pid = getsid(pid)) == -1, pid);
    380 			HX((pid = getppid()) == -1, pid);
    381 			HX((pid = getpgid(0)) == -1, pid);
    382 			HX((e = getpriority(0, 0)) == -1, e);
    383 
    384 			if (!faster) {
    385 				ts.tv_sec = 0;
    386 				ts.tv_nsec = 1;
    387 				(void) nanosleep(&ts, NULL);
    388 			}
    389 
    390 			HX(sigpending(&sigset) == -1, sigset);
    391 			HX(sigprocmask(SIG_BLOCK, NULL, &sigset) == -1,
    392 			    sigset);
    393 
    394 			HF(getentropy);	/* an addr in this library */
    395 			HF(printf);		/* an addr in libc */
    396 			p = (char *)&p;
    397 			HD(p);		/* an addr on stack */
    398 			p = (char *)&errno;
    399 			HD(p);		/* the addr of errno */
    400 
    401 			if (i == 0) {
    402 				struct sockaddr_storage ss;
    403 				struct statvfs stvfs;
    404 				struct termios tios;
    405 				struct statfs stfs;
    406 				socklen_t ssl;
    407 				off_t off;
    408 
    409 				/*
    410 				 * Prime-sized mappings encourage fragmentation;
    411 				 * thus exposing some address entropy.
    412 				 */
    413 				struct mm {
    414 					size_t	npg;
    415 					void	*p;
    416 				} mm[] =	 {
    417 					{ 17, MAP_FAILED }, { 3, MAP_FAILED },
    418 					{ 11, MAP_FAILED }, { 2, MAP_FAILED },
    419 					{ 5, MAP_FAILED }, { 3, MAP_FAILED },
    420 					{ 7, MAP_FAILED }, { 1, MAP_FAILED },
    421 					{ 57, MAP_FAILED }, { 3, MAP_FAILED },
    422 					{ 131, MAP_FAILED }, { 1, MAP_FAILED },
    423 				};
    424 
    425 				for (m = 0; m < sizeof mm/sizeof(mm[0]); m++) {
    426 					HX(mm[m].p = mmap(NULL,
    427 					    mm[m].npg * pgs,
    428 					    PROT_READ|PROT_WRITE,
    429 					    MAP_PRIVATE|MAP_ANON, -1,
    430 					    (off_t)0), mm[m].p);
    431 					if (mm[m].p != MAP_FAILED) {
    432 						size_t mo;
    433 
    434 						/* Touch some memory... */
    435 						p = mm[m].p;
    436 						mo = cnt %
    437 						    (mm[m].npg * pgs - 1);
    438 						p[mo] = 1;
    439 						cnt += (int)((long)(mm[m].p)
    440 						    / pgs);
    441 					}
    442 
    443 					/* Check cnts and times... */
    444 					for (ii = 0; ii < sizeof(cl)/sizeof(cl[0]);
    445 					    ii++) {
    446 						HX((e = clock_gettime(cl[ii],
    447 						    &ts)) == -1, ts);
    448 						if (e != -1)
    449 							cnt += (int)ts.tv_nsec;
    450 					}
    451 
    452 					HX((e = getrusage(RUSAGE_SELF,
    453 					    &ru)) == -1, ru);
    454 					if (e != -1) {
    455 						cnt += (int)ru.ru_utime.tv_sec;
    456 						cnt += (int)ru.ru_utime.tv_usec;
    457 					}
    458 				}
    459 
    460 				for (m = 0; m < sizeof mm/sizeof(mm[0]); m++) {
    461 					if (mm[m].p != MAP_FAILED)
    462 						munmap(mm[m].p, mm[m].npg * pgs);
    463 					mm[m].p = MAP_FAILED;
    464 				}
    465 
    466 				HX(stat(".", &st) == -1, st);
    467 				HX(statvfs(".", &stvfs) == -1, stvfs);
    468 				HX(statfs(".", &stfs) == -1, stfs);
    469 
    470 				HX(stat("/", &st) == -1, st);
    471 				HX(statvfs("/", &stvfs) == -1, stvfs);
    472 				HX(statfs("/", &stfs) == -1, stfs);
    473 
    474 				HX((e = fstat(0, &st)) == -1, st);
    475 				if (e == -1) {
    476 					if (S_ISREG(st.st_mode) ||
    477 					    S_ISFIFO(st.st_mode) ||
    478 					    S_ISSOCK(st.st_mode)) {
    479 						HX(fstatvfs(0, &stvfs) == -1,
    480 						    stvfs);
    481 						HX(fstatfs(0, &stfs) == -1,
    482 						    stfs);
    483 						HX((off = lseek(0, (off_t)0,
    484 						    SEEK_CUR)) < 0, off);
    485 					}
    486 					if (S_ISCHR(st.st_mode)) {
    487 						HX(tcgetattr(0, &tios) == -1,
    488 						    tios);
    489 					} else if (S_ISSOCK(st.st_mode)) {
    490 						memset(&ss, 0, sizeof ss);
    491 						ssl = sizeof(ss);
    492 						HX(getpeername(0,
    493 						    (void *)&ss, &ssl) == -1,
    494 						    ss);
    495 					}
    496 				}
    497 
    498 				HX((e = getrusage(RUSAGE_CHILDREN,
    499 				    &ru)) == -1, ru);
    500 				if (e != -1) {
    501 					cnt += (int)ru.ru_utime.tv_sec;
    502 					cnt += (int)ru.ru_utime.tv_usec;
    503 				}
    504 			} else {
    505 				/* Subsequent hashes absorb previous result */
    506 				HD(results);
    507 			}
    508 
    509 			HX((e = gettimeofday(&tv, NULL)) == -1, tv);
    510 			if (e != -1) {
    511 				cnt += (int)tv.tv_sec;
    512 				cnt += (int)tv.tv_usec;
    513 			}
    514 
    515 			HD(cnt);
    516 		}
    517 #ifdef HAVE_GETAUXVAL
    518 #ifdef AT_RANDOM
    519 		/* Not as random as you think but we take what we are given */
    520 		p = (char *) getauxval(AT_RANDOM);
    521 		if (p)
    522 			HR(p, 16);
    523 #endif
    524 #ifdef AT_SYSINFO_EHDR
    525 		p = (char *) getauxval(AT_SYSINFO_EHDR);
    526 		if (p)
    527 			HR(p, pgs);
    528 #endif
    529 #ifdef AT_BASE
    530 		p = (char *) getauxval(AT_BASE);
    531 		if (p)
    532 			HD(p);
    533 #endif
    534 #endif
    535 
    536 		SHA512_Final(results, &ctx);
    537 		memcpy((char *)buf + i, results, min(sizeof(results), len - i));
    538 		i += min(sizeof(results), len - i);
    539 	}
    540 	explicit_bzero(&ctx, sizeof ctx);
    541 	explicit_bzero(results, sizeof results);
    542 	if (gotdata(buf, len) == 0) {
    543 		errno = save_errno;
    544 		return 0;		/* satisfied */
    545 	}
    546 	errno = EIO;
    547 	return -1;
    548 }