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retrying syscall and calls to hardware rng

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This commit is contained in:
Logan007 2020-07-27 20:55:36 +05:45
parent 5bcfd9a234
commit dc9b1449ab
1 changed files with 55 additions and 9 deletions
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64
src/random_numbers.c
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@ -16,8 +16,16 @@
*
*/
#ifdef SYS_getrandom
#include <errno.h>
#endif
#include "n2n.h"
// syscall and inquiring random number from hardware generators might fail, so we will retry
#define RND_RETRIES 1000
/* The following code offers an alterate pseudo random number generator
namely XORSHIFT128+ to use instead of C's rand(). Its performance is
on par with C's rand().
@ -93,24 +101,62 @@ uint64_t n2n_rand () {
state yet, a call to n2n_srand ( n2n_seed() ) would do. */
uint64_t n2n_seed (void) {
uint64_t seed = 0;
uint64_t ret = 0;
uint64_t seed;
uint64_t ret;
size_t i;
#ifdef SYS_getrandom
syscall (SYS_getrandom, &seed, sizeof(seed), GRND_NONBLOCK);
ret += seed;
int rc = -1;
for(i = 0; (i < RND_RETRIES) && (rc != sizeof(seed)); i++) {
rc = syscall (SYS_getrandom, &seed, sizeof(seed), GRND_NONBLOCK);
// if successful, rc should contain the requested number of random bytes
if(rc != sizeof(seed)) {
if (errno != EAGAIN) {
traceEvent(TRACE_ERROR, "n2n_seed faced error errno=%u from getrandom syscall.", errno);
break;
}
}
}
// if we still see an EAGAIN error here, we must have run out of retries
if(errno == EAGAIN) {
traceEvent(TRACE_ERROR, "n2n_seed saw getrandom syscall indicate not being able to provide enough entropy yet.");
}
#endif
// as we want randomness, it does no harm to add up even uninitialized values or
// erroneously arbitrary values returned from the syscall for the first time
ret += seed;
// __RDRND__ is set only if architecturual feature is set, e.g. compile with -march=native
#ifdef __RDRND__
_rdrand64_step ((unsigned long long*)&seed);
ret += seed;
for(i = 0; i < RND_RETRIES; i++) {
if(_rdrand64_step ((unsigned long long*)&seed)) {
// success!
// from now on, we keep this inside the loop because in case of failure
// and with unchanged values, we do not want to double the previous value
ret += seed;
break;
}
// continue loop to try again otherwise
}
if(i == RND_RETRIES){
traceEvent(TRACE_ERROR, "n2n_seed was not able to get a hardware generated random number from RDRND.");
}
#endif
// __RDSEED__ ist set only if architecturual feature is set, e.g. compile with -march=native
#ifdef __RDSEED__
_rdseed64_step((unsigned long long*)&seed);
ret += seed;
for(i = 0; i < RND_RETRIES; i++) {
if(_rdseed64_step((unsigned long long*)&seed)) {
// success!
ret += seed;
break;
}
// continue loop to try again otherwise
}
if(i == RND_RETRIES){
traceEvent(TRACE_ERROR, "n2n_seed was not able to get a hardware generated random number from RDSEED.");
}
#endif
/* The WIN32 code is still untested and thus commented
@ -126,7 +172,7 @@ uint64_t n2n_seed (void) {
seed = time(NULL); /* UTC in seconds */
ret += seed;
seed = clock() * 8996146197; /* clock() = ticks since program start */
seed = clock() * 18444244737; /* clock() = ticks since program start */
ret += seed;
return ret;