diff options
Diffstat (limited to 'src/basic/random-util.c')
| -rw-r--r-- | src/basic/random-util.c | 251 |
1 files changed, 251 insertions, 0 deletions
diff --git a/src/basic/random-util.c b/src/basic/random-util.c new file mode 100644 index 0000000..200a914 --- /dev/null +++ b/src/basic/random-util.c @@ -0,0 +1,251 @@ +/* SPDX-License-Identifier: LGPL-2.1-or-later */ + +#include <elf.h> +#include <errno.h> +#include <fcntl.h> +#include <linux/random.h> +#include <pthread.h> +#include <stdbool.h> +#include <stdint.h> +#include <stdlib.h> +#include <string.h> +#include <sys/ioctl.h> +#include <sys/time.h> + +#if HAVE_SYS_AUXV_H +# include <sys/auxv.h> +#endif + +#include "alloc-util.h" +#include "env-util.h" +#include "errno-util.h" +#include "fd-util.h" +#include "fileio.h" +#include "io-util.h" +#include "missing_random.h" +#include "missing_syscall.h" +#include "missing_threads.h" +#include "parse-util.h" +#include "random-util.h" +#include "sha256.h" +#include "time-util.h" + +/* This is a "best effort" kind of thing, but has no real security value. So, this should only be used by + * random_bytes(), which is not meant for crypto. This could be made better, but we're *not* trying to roll a + * userspace prng here, or even have forward secrecy, but rather just do the shortest thing that is at least + * better than libc rand(). */ +static void fallback_random_bytes(void *p, size_t n) { + static thread_local uint64_t fallback_counter = 0; + struct { + char label[32]; + uint64_t call_id, block_id; + usec_t stamp_mono, stamp_real; + pid_t pid, tid; + uint8_t auxval[16]; + } state = { + /* Arbitrary domain separation to prevent other usage of AT_RANDOM from clashing. */ + .label = "systemd fallback random bytes v1", + .call_id = fallback_counter++, + .stamp_mono = now(CLOCK_MONOTONIC), + .stamp_real = now(CLOCK_REALTIME), + .pid = getpid(), + .tid = gettid(), + }; + +#if HAVE_SYS_AUXV_H + memcpy(state.auxval, ULONG_TO_PTR(getauxval(AT_RANDOM)), sizeof(state.auxval)); +#endif + + while (n > 0) { + struct sha256_ctx ctx; + + sha256_init_ctx(&ctx); + sha256_process_bytes(&state, sizeof(state), &ctx); + if (n < SHA256_DIGEST_SIZE) { + uint8_t partial[SHA256_DIGEST_SIZE]; + sha256_finish_ctx(&ctx, partial); + memcpy(p, partial, n); + break; + } + sha256_finish_ctx(&ctx, p); + p = (uint8_t *) p + SHA256_DIGEST_SIZE; + n -= SHA256_DIGEST_SIZE; + ++state.block_id; + } +} + +void random_bytes(void *p, size_t n) { + static bool have_getrandom = true, have_grndinsecure = true; + _cleanup_close_ int fd = -1; + + if (n == 0) + return; + + for (;;) { + ssize_t l; + + if (!have_getrandom) + break; + + l = getrandom(p, n, have_grndinsecure ? GRND_INSECURE : GRND_NONBLOCK); + if (l > 0) { + if ((size_t) l == n) + return; /* Done reading, success. */ + p = (uint8_t *) p + l; + n -= l; + continue; /* Interrupted by a signal; keep going. */ + } else if (l == 0) + break; /* Weird, so fallback to /dev/urandom. */ + else if (ERRNO_IS_NOT_SUPPORTED(errno)) { + have_getrandom = false; + break; /* No syscall, so fallback to /dev/urandom. */ + } else if (errno == EINVAL && have_grndinsecure) { + have_grndinsecure = false; + continue; /* No GRND_INSECURE; fallback to GRND_NONBLOCK. */ + } else if (errno == EAGAIN && !have_grndinsecure) + break; /* Will block, but no GRND_INSECURE, so fallback to /dev/urandom. */ + + break; /* Unexpected, so just give up and fallback to /dev/urandom. */ + } + + fd = open("/dev/urandom", O_RDONLY|O_CLOEXEC|O_NOCTTY); + if (fd >= 0 && loop_read_exact(fd, p, n, false) == 0) + return; + + /* This is a terrible fallback. Oh well. */ + fallback_random_bytes(p, n); +} + +int crypto_random_bytes(void *p, size_t n) { + static bool have_getrandom = true, seen_initialized = false; + _cleanup_close_ int fd = -1; + + if (n == 0) + return 0; + + for (;;) { + ssize_t l; + + if (!have_getrandom) + break; + + l = getrandom(p, n, 0); + if (l > 0) { + if ((size_t) l == n) + return 0; /* Done reading, success. */ + p = (uint8_t *) p + l; + n -= l; + continue; /* Interrupted by a signal; keep going. */ + } else if (l == 0) + return -EIO; /* Weird, should never happen. */ + else if (ERRNO_IS_NOT_SUPPORTED(errno)) { + have_getrandom = false; + break; /* No syscall, so fallback to /dev/urandom. */ + } + return -errno; + } + + if (!seen_initialized) { + _cleanup_close_ int ready_fd = -1; + int r; + + ready_fd = open("/dev/random", O_RDONLY|O_CLOEXEC|O_NOCTTY); + if (ready_fd < 0) + return -errno; + r = fd_wait_for_event(ready_fd, POLLIN, USEC_INFINITY); + if (r < 0) + return r; + seen_initialized = true; + } + + fd = open("/dev/urandom", O_RDONLY|O_CLOEXEC|O_NOCTTY); + if (fd < 0) + return -errno; + return loop_read_exact(fd, p, n, false); +} + +size_t random_pool_size(void) { + _cleanup_free_ char *s = NULL; + int r; + + /* Read pool size, if possible */ + r = read_one_line_file("/proc/sys/kernel/random/poolsize", &s); + if (r < 0) + log_debug_errno(r, "Failed to read pool size from kernel: %m"); + else { + unsigned sz; + + r = safe_atou(s, &sz); + if (r < 0) + log_debug_errno(r, "Failed to parse pool size: %s", s); + else + /* poolsize is in bits on 2.6, but we want bytes */ + return CLAMP(sz / 8, RANDOM_POOL_SIZE_MIN, RANDOM_POOL_SIZE_MAX); + } + + /* Use the minimum as default, if we can't retrieve the correct value */ + return RANDOM_POOL_SIZE_MIN; +} + +int random_write_entropy(int fd, const void *seed, size_t size, bool credit) { + _cleanup_close_ int opened_fd = -1; + int r; + + assert(seed || size == 0); + + if (size == 0) + return 0; + + if (fd < 0) { + opened_fd = open("/dev/urandom", O_WRONLY|O_CLOEXEC|O_NOCTTY); + if (opened_fd < 0) + return -errno; + + fd = opened_fd; + } + + if (credit) { + _cleanup_free_ struct rand_pool_info *info = NULL; + + /* The kernel API only accepts "int" as entropy count (which is in bits), let's avoid any + * chance for confusion here. */ + if (size > INT_MAX / 8) + return -EOVERFLOW; + + info = malloc(offsetof(struct rand_pool_info, buf) + size); + if (!info) + return -ENOMEM; + + info->entropy_count = size * 8; + info->buf_size = size; + memcpy(info->buf, seed, size); + + if (ioctl(fd, RNDADDENTROPY, info) < 0) + return -errno; + } else { + r = loop_write(fd, seed, size, false); + if (r < 0) + return r; + } + + return 1; +} + +uint64_t random_u64_range(uint64_t m) { + uint64_t x, remainder; + + /* Generates a random number in the range 0…m-1, unbiased. (Java's algorithm) */ + + if (m == 0) /* Let's take m == 0 as special case to return an integer from the full range */ + return random_u64(); + if (m == 1) + return 0; + + remainder = UINT64_MAX % m; + + do { + x = random_u64(); + } while (x >= UINT64_MAX - remainder); + + return x % m; +} |