using unbiased rand_below
MODIFY
include/afl-fuzz.h
include/afl-fuzz.h
@@ -1027,7 +1027,12 @@ static inline u32 rand_below(afl_state_t *afl, u32 limit) {
}
- return rand_next(afl) % limit;
+ /* Modulo is biased - we don't want our fuzzing to be biased so let's do it right. */
+ u64 unbiased_rnd;
+ do {
+ unbiased_rnd = rand_next(afl);
+ } while (unbiased_rnd >= (UINT64_MAX - (UINT64_MAX % limit)));
+ return unbiased_rnd % limit;
}

using unbiased rand_below