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util/rand_xor: use getrandom() when available

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This function has been added in glibc 2.25, and the related syscall in
Linux 3.17, in order to avoid requiring the /dev/urandom to exist, and
doing the open()/read()/close() dance on it.

We pass GRND_NONBLOCK so that it doesn’t block if not enough entropy has
been gathered to initialise the /dev/urandom source, and fallback to the
next source in any error case.

Signed-off-by: Emmanuel Gil Peyrot <linkmauve@linkmauve.fr>
Reviewed-by: Eric Engestrom <eric.engestrom@intel.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/2026>
This commit is contained in:
Emmanuel Gil Peyrot
2019-09-18 13:20:57 +02:00
parent cf2b285c55
commit 4c212a1168
2 changed files with 12 additions and 2 deletions
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2
meson.build
View File

@@ -1163,7 +1163,7 @@ foreach h : ['xlocale.h', 'sys/sysctl.h', 'linux/futex.h', 'endian.h', 'dlfcn.h'
endif endif
endforeach endforeach
foreach f : ['strtof', 'mkostemp', 'timespec_get', 'memfd_create', 'random_r', 'flock', 'strtok_r'] foreach f : ['strtof', 'mkostemp', 'timespec_get', 'memfd_create', 'random_r', 'flock', 'strtok_r', 'getrandom']
if cc.has_function(f) if cc.has_function(f)
pre_args += '-DHAVE_@0@'.format(f.to_upper()) pre_args += '-DHAVE_@0@'.format(f.to_upper())
endif endif

12
src/util/rand_xor.c
View File

@@ -23,6 +23,9 @@
*/ */
#if defined(__linux__) #if defined(__linux__)
#if defined(HAVE_GETRANDOM)
#include <sys/random.h>
#endif
#include <sys/file.h> #include <sys/file.h>
#include <unistd.h> #include <unistd.h>
#include <fcntl.h> #include <fcntl.h>
@@ -58,11 +61,18 @@ s_rand_xorshift128plus(uint64_t *seed, bool randomised_seed)
goto fixed_seed; goto fixed_seed;
#if defined(__linux__) #if defined(__linux__)
size_t seed_size = sizeof(uint64_t) * 2;
#if defined(HAVE_GETRANDOM)
ssize_t ret = getrandom(seed, seed_size, GRND_NONBLOCK);
if (ret == seed_size)
return;
#endif
int fd = open("/dev/urandom", O_RDONLY); int fd = open("/dev/urandom", O_RDONLY);
if (fd < 0) if (fd < 0)
goto fixed_seed; goto fixed_seed;
size_t seed_size = sizeof(uint64_t) * 2;
if (read(fd, seed, seed_size) != seed_size) { if (read(fd, seed, seed_size) != seed_size) {
close(fd); close(fd);
goto fixed_seed; goto fixed_seed;