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Diffstat (limited to 'src/libbasic/src/random-util.c')
-rw-r--r-- | src/libbasic/src/random-util.c | 133 |
1 files changed, 133 insertions, 0 deletions
diff --git a/src/libbasic/src/random-util.c b/src/libbasic/src/random-util.c new file mode 100644 index 0000000000..2f468db770 --- /dev/null +++ b/src/libbasic/src/random-util.c @@ -0,0 +1,133 @@ +/*** + This file is part of systemd. + + Copyright 2010 Lennart Poettering + + systemd 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. + + systemd 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 systemd; If not, see <http://www.gnu.org/licenses/>. +***/ + +#include <elf.h> +#include <errno.h> +#include <fcntl.h> +#include <stdbool.h> +#include <stdlib.h> +#include <sys/time.h> +#include <linux/random.h> +#include <stdint.h> + +#ifdef HAVE_SYS_AUXV_H +#include <sys/auxv.h> +#endif + +#include "fd-util.h" +#include "io-util.h" +#include "missing.h" +#include "random-util.h" +#include "time-util.h" + +int dev_urandom(void *p, size_t n) { + static int have_syscall = -1; + + _cleanup_close_ int fd = -1; + int r; + + /* Gathers some randomness from the kernel. This call will + * never block, and will always return some data from the + * kernel, regardless if the random pool is fully initialized + * or not. It thus makes no guarantee for the quality of the + * returned entropy, but is good enough for or usual usecases + * of seeding the hash functions for hashtable */ + + /* Use the getrandom() syscall unless we know we don't have + * it, or when the requested size is too large for it. */ + if (have_syscall != 0 || (size_t) (int) n != n) { + r = getrandom(p, n, GRND_NONBLOCK); + if (r == (int) n) { + have_syscall = true; + return 0; + } + + if (r < 0) { + if (errno == ENOSYS) + /* we lack the syscall, continue with + * reading from /dev/urandom */ + have_syscall = false; + else if (errno == EAGAIN) + /* not enough entropy for now. Let's + * remember to use the syscall the + * next time, again, but also read + * from /dev/urandom for now, which + * doesn't care about the current + * amount of entropy. */ + have_syscall = true; + else + return -errno; + } else + /* too short read? */ + return -ENODATA; + } + + fd = open("/dev/urandom", O_RDONLY|O_CLOEXEC|O_NOCTTY); + if (fd < 0) + return errno == ENOENT ? -ENOSYS : -errno; + + return loop_read_exact(fd, p, n, true); +} + +void initialize_srand(void) { + static bool srand_called = false; + unsigned x; +#ifdef HAVE_SYS_AUXV_H + void *auxv; +#endif + + if (srand_called) + return; + +#ifdef HAVE_SYS_AUXV_H + /* The kernel provides us with 16 bytes of entropy in auxv, so let's try to make use of that to seed the + * pseudo-random generator. It's better than nothing... */ + + auxv = (void*) getauxval(AT_RANDOM); + if (auxv) { + assert_cc(sizeof(x) < 16); + memcpy(&x, auxv, sizeof(x)); + } else +#endif + x = 0; + + + x ^= (unsigned) now(CLOCK_REALTIME); + x ^= (unsigned) gettid(); + + srand(x); + srand_called = true; +} + +void random_bytes(void *p, size_t n) { + uint8_t *q; + int r; + + r = dev_urandom(p, n); + if (r >= 0) + return; + + /* If some idiot made /dev/urandom unavailable to us, he'll + * get a PRNG instead. */ + + initialize_srand(); + + for (q = p; q < (uint8_t*) p + n; q ++) + *q = rand(); +} |