diff options
Diffstat (limited to 'stdlib/arc4random.c')
| -rw-r--r-- | stdlib/arc4random.c | 208 |
1 files changed, 208 insertions, 0 deletions
diff --git a/stdlib/arc4random.c b/stdlib/arc4random.c new file mode 100644 index 0000000000..65547e79aa --- /dev/null +++ b/stdlib/arc4random.c @@ -0,0 +1,208 @@ +/* Pseudo Random Number Generator based on ChaCha20. + Copyright (C) 2022 Free Software Foundation, Inc. + This file is part of the GNU C Library. + + The GNU C Library is free software; you can redistribute it and/or + modify it under the terms of the GNU Lesser General Public + License as published by the Free Software Foundation; either + version 2.1 of the License, or (at your option) any later version. + + The GNU C Library is distributed in the hope that it will be useful, + but WITHOUT ANY WARRANTY; without even the implied warranty of + MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU + Lesser General Public License for more details. + + You should have received a copy of the GNU Lesser General Public + License along with the GNU C Library; if not, see + <https://www.gnu.org/licenses/>. */ + +#include <arc4random.h> +#include <errno.h> +#include <not-cancel.h> +#include <stdio.h> +#include <stdlib.h> +#include <sys/mman.h> +#include <sys/param.h> +#include <sys/random.h> +#include <tls-internal.h> + +/* arc4random keeps two counters: 'have' is the current valid bytes not yet + consumed in 'buf' while 'count' is the maximum number of bytes until a + reseed. + + Both the initial seed and reseed try to obtain entropy from the kernel + and abort the process if none could be obtained. + + The state 'buf' improves the usage of the cipher calls, allowing to call + optimized implementations (if the architecture provides it) and minimize + function call overhead. */ + +#include <chacha20.c> + +/* Called from the fork function to reset the state. */ +void +__arc4random_fork_subprocess (void) +{ + struct arc4random_state_t *state = __glibc_tls_internal ()->rand_state; + if (state != NULL) + { + explicit_bzero (state, sizeof (*state)); + /* Force key init. */ + state->count = -1; + } +} + +/* Return the current thread random state or try to create one if there is + none available. In the case malloc can not allocate a state, arc4random + will try to get entropy with arc4random_getentropy. */ +static struct arc4random_state_t * +arc4random_get_state (void) +{ + struct arc4random_state_t *state = __glibc_tls_internal ()->rand_state; + if (state == NULL) + { + state = malloc (sizeof (struct arc4random_state_t)); + if (state != NULL) + { + /* Force key initialization on first call. */ + state->count = -1; + __glibc_tls_internal ()->rand_state = state; + } + } + return state; +} + +static void +arc4random_getrandom_failure (void) +{ + __libc_fatal ("Fatal glibc error: cannot get entropy for arc4random\n"); +} + +static void +arc4random_rekey (struct arc4random_state_t *state, uint8_t *rnd, size_t rndlen) +{ + chacha20_crypt (state->ctx, state->buf, state->buf, sizeof state->buf); + + /* Mix optional user provided data. */ + if (rnd != NULL) + { + size_t m = MIN (rndlen, CHACHA20_KEY_SIZE + CHACHA20_IV_SIZE); + for (size_t i = 0; i < m; i++) + state->buf[i] ^= rnd[i]; + } + + /* Immediately reinit for backtracking resistance. */ + chacha20_init (state->ctx, state->buf, state->buf + CHACHA20_KEY_SIZE); + explicit_bzero (state->buf, CHACHA20_KEY_SIZE + CHACHA20_IV_SIZE); + state->have = sizeof (state->buf) - (CHACHA20_KEY_SIZE + CHACHA20_IV_SIZE); +} + +static void +arc4random_getentropy (void *rnd, size_t len) +{ + if (__getrandom_nocancel (rnd, len, GRND_NONBLOCK) == len) + return; + + int fd = TEMP_FAILURE_RETRY (__open64_nocancel ("/dev/urandom", + O_RDONLY | O_CLOEXEC)); + if (fd != -1) + { + uint8_t *p = rnd; + uint8_t *end = p + len; + do + { + ssize_t ret = TEMP_FAILURE_RETRY (__read_nocancel (fd, p, end - p)); + if (ret <= 0) + arc4random_getrandom_failure (); + p += ret; + } + while (p < end); + + if (__close_nocancel (fd) == 0) + return; + } + arc4random_getrandom_failure (); +} + +/* Check if the thread context STATE should be reseed with kernel entropy + depending of requested LEN bytes. If there is less than requested, + the state is either initialized or reseeded, otherwise the internal + counter subtract the requested length. */ +static void +arc4random_check_stir (struct arc4random_state_t *state, size_t len) +{ + if (state->count <= len || state->count == -1) + { + uint8_t rnd[CHACHA20_KEY_SIZE + CHACHA20_IV_SIZE]; + arc4random_getentropy (rnd, sizeof rnd); + + if (state->count == -1) + chacha20_init (state->ctx, rnd, rnd + CHACHA20_KEY_SIZE); + else + arc4random_rekey (state, rnd, sizeof rnd); + + explicit_bzero (rnd, sizeof rnd); + + /* Invalidate the buf. */ + state->have = 0; + memset (state->buf, 0, sizeof state->buf); + state->count = CHACHA20_RESEED_SIZE; + } + else + state->count -= len; +} + +void +__arc4random_buf (void *buffer, size_t len) +{ + struct arc4random_state_t *state = arc4random_get_state (); + if (__glibc_unlikely (state == NULL)) + { + arc4random_getentropy (buffer, len); + return; + } + + arc4random_check_stir (state, len); + while (len > 0) + { + if (state->have > 0) + { + size_t m = MIN (len, state->have); + uint8_t *ks = state->buf + sizeof (state->buf) - state->have; + memcpy (buffer, ks, m); + explicit_bzero (ks, m); + buffer += m; + len -= m; + state->have -= m; + } + if (state->have == 0) + arc4random_rekey (state, NULL, 0); + } +} +libc_hidden_def (__arc4random_buf) +weak_alias (__arc4random_buf, arc4random_buf) + +uint32_t +__arc4random (void) +{ + uint32_t r; + + struct arc4random_state_t *state = arc4random_get_state (); + if (__glibc_unlikely (state == NULL)) + { + arc4random_getentropy (&r, sizeof (uint32_t)); + return r; + } + + arc4random_check_stir (state, sizeof (uint32_t)); + if (state->have < sizeof (uint32_t)) + arc4random_rekey (state, NULL, 0); + uint8_t *ks = state->buf + sizeof (state->buf) - state->have; + memcpy (&r, ks, sizeof (uint32_t)); + memset (ks, 0, sizeof (uint32_t)); + state->have -= sizeof (uint32_t); + + return r; +} +libc_hidden_def (__arc4random) +weak_alias (__arc4random, arc4random) |