crypto: testmgr - generate power-of-2 lengths more often

Implementations of hash functions often have special cases when lengths
are a multiple of the hash function's internal block size (e.g. 64 for
SHA-256, 128 for SHA-512).  Currently, when the fuzz testing code
generates lengths, it doesn't prefer any length mod 64 over any other.
This limits the coverage of these special cases.

Therefore, this patch updates the fuzz testing code to generate
power-of-2 lengths and divide messages exactly in half a bit more often.

Reviewed-by: Sami Tolvanen <samitolvanen@google.com>
Acked-by: Ard Biesheuvel <ardb@kernel.org>
Signed-off-by: Eric Biggers <ebiggers@google.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>

diff --git a/crypto/testmgr.c b/crypto/testmgr.c
index a780b615f8c6052f2a32cec4c463deb7ef023486..f02cb075bd68114482a87f6e89c7552b27c49a64 100644 (file)
--- a/crypto/testmgr.c
+++ b/crypto/testmgr.c
@@ -916,14 +916,20 @@ static unsigned int generate_random_length(struct rnd_state *rng,
 
        switch (prandom_u32_below(rng, 4)) {
        case 0:
-               return len % 64;
+               len %= 64;
+               break;
        case 1:
-               return len % 256;
+               len %= 256;
+               break;
        case 2:
-               return len % 1024;
+               len %= 1024;
+               break;
        default:
-               return len;
+               break;
        }
+       if (len && prandom_u32_below(rng, 4) == 0)
+               len = rounddown_pow_of_two(len);
+       return len;
 }
 
 /* Flip a random bit in the given nonempty data buffer */
@@ -1019,6 +1025,8 @@ static char *generate_random_sgl_divisions(struct rnd_state *rng,
 
                if (div == &divs[max_divs - 1] || prandom_bool(rng))
                        this_len = remaining;
+               else if (prandom_u32_below(rng, 4) == 0)
+                       this_len = (remaining + 1) / 2;
                else
                        this_len = prandom_u32_inclusive(rng, 1, remaining);
                div->proportion_of_total = this_len;