Merge bitcoin#627: Guard memcmp in tests against mixed size inputs.

248bffb Guard memcmp in tests against mixed size inputs. (Gregory Maxwell)

Pull request description:

  Reported by real-or-random.

  Fixes bitcoin#623.

ACKs for commit 248bff:
  practicalswift:
    utACK 248bffb

Tree-SHA512: 29867c79d2d6852f495334a5a9129c7feac2df639dd7f752067380689b0ce9f9b35e94524834c01e698df5c0b83dc9855204ec09f5dfe488a388b509c9b861d9

src/tests.c

@@ -4455,7 +4455,7 @@ int test_ecdsa_der_parse(const unsigned char *sig, size_t siglen, int certainly_
     if (valid_der) {
         ret |= (!roundtrips_der_lax) << 12;
         ret |= (len_der != len_der_lax) << 13;
-        ret |= (memcmp(roundtrip_der_lax, roundtrip_der, len_der) != 0) << 14;
+        ret |= ((len_der != len_der_lax) || (memcmp(roundtrip_der_lax, roundtrip_der, len_der) != 0)) << 14;
     }
     ret |= (roundtrips_der != roundtrips_der_lax) << 15;
     if (parsed_der) {
@@ -4496,7 +4496,7 @@ int test_ecdsa_der_parse(const unsigned char *sig, size_t siglen, int certainly_
     ret |= (roundtrips_der != roundtrips_openssl) << 7;
     if (roundtrips_openssl) {
         ret |= (len_der != (size_t)len_openssl) << 8;
-        ret |= (memcmp(roundtrip_der, roundtrip_openssl, len_der) != 0) << 9;
+        ret |= ((len_der != (size_t)len_openssl) || (memcmp(roundtrip_der, roundtrip_openssl, len_der) != 0)) << 9;
     }
 #endif
     return ret;