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random.c
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random.c
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/*
* Copyright (C) 2023 National Cheng Kung University, Taiwan.
* Copyright (c) 2017 Daan Sprenkels <daan@dsprenkels.com>
*
* Permission is hereby granted, free of charge, to any person obtaining a copy
* of this software and associated documentation files (the "Software"), to deal
* in the Software without restriction, including without limitation the rights
* to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
* copies of the Software, and to permit persons to whom the Software is
* furnished to do so, subject to the following conditions:
*
* The above copyright notice and this permission notice shall be included in
* all copies or substantial portions of the Software.
*
* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
* IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
* FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
* AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
* LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
* OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
* THE SOFTWARE.
*/
/* In the case that are compiling on linux, we need to define _GNU_SOURCE
* *before* random.h is included. Otherwise SYS_getrandom will not be declared.
*/
#if defined(__linux__) || defined(__GNU__)
#define _GNU_SOURCE
#endif
#include "random.h"
#if defined(__linux__) || defined(__GNU__)
/* We would need to include <linux/random.h>, but not every target has access
* to the linux headers. We only need RNDGETENTCNT, so we instead inline it.
* RNDGETENTCNT is originally defined in `include/uapi/linux/random.h` in the
* Linux kernel source.
*/
#define RNDGETENTCNT 0x80045200
#include <assert.h>
#include <errno.h>
#include <fcntl.h>
#include <poll.h>
#include <stdint.h>
#include <stdio.h>
#include <sys/ioctl.h>
#if (defined(__linux__) || defined(__GNU__)) && defined(__GLIBC__) && \
((__GLIBC__ > 2) || (__GLIBC_MINOR__ > 24))
#define USE_GLIBC
#include <sys/random.h>
#endif
#include <sys/stat.h>
#include <sys/syscall.h>
#include <sys/types.h>
#include <unistd.h>
/* We need SSIZE_MAX as the maximum read len from /dev/urandom */
#if !defined(SSIZE_MAX)
#include <bits/wordsize.h>
#if __WORDSIZE == 64
#define SSIZE_MAX LONG_MAX
#else
#define SSIZE_MAX INT_MAX
#endif
#endif
#endif /* defined(__linux__) || defined(__GNU__) */
#if defined(__unix__) || (defined(__APPLE__) && defined(__MACH__))
/* Dragonfly, FreeBSD, NetBSD, OpenBSD (has arc4random) */
#include <sys/param.h>
#if defined(BSD)
#include <stdlib.h>
#endif
/* GNU/Hurd defines BSD in sys/param.h which causes problems later */
#if defined(__GNU__)
#undef BSD
#endif
#endif
#if (defined(__linux__) || defined(__GNU__)) && \
(defined(USE_GLIBC) || defined(SYS_getrandom))
#if defined(USE_GLIBC)
/* getrandom is declared in glibc. */
#elif defined(SYS_getrandom)
static ssize_t getrandom(void *buf, size_t buflen, unsigned int flags)
{
return syscall(SYS_getrandom, buf, buflen, flags);
}
#endif
static int linux_getrandom(void *buf, size_t n)
{
size_t offset = 0;
int ret;
while (n > 0) {
/* getrandom does not allow chunks larger than 33554431 */
size_t chunk = n <= 33554431 ? n : 33554431;
do {
ret = getrandom((char *) buf + offset, chunk, 0);
} while (ret == -1 && errno == EINTR);
if (ret < 0)
return ret;
offset += ret;
n -= ret;
}
assert(n == 0);
return 0;
}
#endif /* (defined(__linux__) || defined(__GNU__)) && (defined(USE_GLIBC) || \
defined(SYS_getrandom)) */
#if defined(__linux__) && !defined(SYS_getrandom)
#if defined(__linux__)
static inline int linux_read_entropy_ioctl(int device, int *entropy)
{
return ioctl(device, RNDGETENTCNT, entropy);
}
static int linux_read_entropy_proc(FILE *stream, int *entropy)
{
int retcode;
do {
rewind(stream);
retcode = fscanf(stream, "%d", entropy);
} while (retcode != 1 && errno == EINTR);
if (retcode != 1)
return -1;
return 0;
}
static int linux_wait_for_entropy(int device)
{
/* We will block on /dev/random, because any increase in the OS' entropy
* level will unblock the request. I use poll here (as does libsodium),
* because we don't *actually* want to read from the device.
*/
enum { IOCTL, PROC } strategy = IOCTL;
const int bits = 128;
FILE *proc_file;
int retcode_error = 0; /* Used as return codes */
int entropy = 0;
/* If the device has enough entropy already, we will want to return early */
int retcode = linux_read_entropy_ioctl(device, &entropy);
if (retcode != 0 && (errno == ENOTTY || errno == ENOSYS)) {
/* The ioctl call on /dev/urandom has failed due to a
* - ENOTTY (unsupported action), or
* - ENOSYS (invalid ioctl; this happens on MIPS).
*
* We will fall back to reading from
* /proc/sys/kernel/random/entropy_avail . This is less ideal,
* because it allocates a file descriptor, and it may not work
* in a chroot. But at this point it seems we have no better
* options left.
*/
strategy = PROC;
/* Open the entropy count file */
proc_file = fopen("/proc/sys/kernel/random/entropy_avail", "r");
if (!proc_file)
return -1;
} else if (retcode != 0) {
/* Unrecoverable ioctl error */
return -1;
}
if (entropy >= bits)
return 0;
int fd;
do {
fd = open("/dev/random", O_RDONLY);
} while (fd == -1 && errno == EINTR); /* EAGAIN will not occur */
if (fd == -1) {
/* Unrecoverable IO error */
return -1;
}
struct pollfd pfd = {.fd = fd, .events = POLLIN};
for (;;) {
retcode = poll(&pfd, 1, -1);
if (retcode == -1 && (errno == EINTR || errno == EAGAIN)) {
continue;
} else if (retcode == 1) {
if (strategy == IOCTL) {
retcode = linux_read_entropy_ioctl(device, &entropy);
} else if (strategy == PROC) {
retcode = linux_read_entropy_proc(proc_file, &entropy);
} else {
return -1; /* Unreachable */
}
if (retcode != 0) {
/* Unrecoverable I/O error */
retcode_error = retcode;
break;
}
if (entropy >= bits)
break;
} else {
/* Unreachable: poll() should only return -1 or 1 */
retcode_error = -1;
break;
}
}
do {
retcode = close(fd);
} while (retcode == -1 && errno == EINTR);
if (strategy == PROC) {
do {
retcode = fclose(proc_file);
} while (retcode == -1 && errno == EINTR);
}
if (retcode_error != 0)
return retcode_error;
return retcode;
}
#endif /* defined(__linux__) */
static int linux_urandom(void *buf, size_t n)
{
int fd;
do {
fd = open("/dev/urandom", O_RDONLY);
} while (fd == -1 && errno == EINTR);
if (fd == -1)
return -1;
#if defined(__linux__)
if (linux_wait_for_entropy(fd) == -1)
return -1;
#endif
size_t offset = 0;
while (n > 0) {
size_t count = n <= SSIZE_MAX ? n : SSIZE_MAX;
ssize_t tmp = read(fd, (char *) buf + offset, count);
if (tmp == -1 && (errno == EAGAIN || errno == EINTR))
continue;
if (tmp == -1)
return -1; /* Unrecoverable IO error */
offset += tmp;
n -= tmp;
}
close(fd);
assert(n == 0);
return 0;
}
#endif /* defined(__linux__) && !defined(SYS_getrandom) */
#if defined(BSD)
#if defined(__APPLE__)
#include <AvailabilityMacros.h>
#if defined(MAC_OS_X_VERSION_10_10) && \
MAC_OS_X_VERSION_MAX_ALLOWED >= MAC_OS_X_VERSION_10_10
#include <CommonCrypto/CommonCryptoError.h>
#include <CommonCrypto/CommonRandom.h>
#endif
#endif
static int bsd_randombytes(void *buf, size_t n)
{
#if defined(MAC_OS_X_VERSION_10_15) && \
MAC_OS_X_VERSION_MAX_ALLOWED >= MAC_OS_X_VERSION_10_15
/* We prefer CCRandomGenerateBytes as it returns an error code while
* arc4random_buf may fail silently on macOS.
*/
return (CCRandomGenerateBytes(buf, n) == kCCSuccess);
#else
arc4random_buf(buf, n);
return 0;
#endif
}
#endif
int randombytes(uint8_t *buf, size_t n)
{
#if defined(__linux__) || defined(__GNU__)
#if defined(USE_GLIBC)
/* Use getrandom system call */
return linux_getrandom(buf, n);
#elif defined(SYS_getrandom)
/* Use getrandom system call */
return linux_getrandom(buf, n);
#else
/* When we have enough entropy, we can read from /dev/urandom */
return linux_urandom(buf, n);
#endif
#elif defined(BSD)
return bsd_randombytes(buf, n);
#else
#error "randombytes(...) is not supported on this platform"
#endif
}