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The fuzzer has managed to generated DSS key/signature pairs that

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verify. Avoid false positives from bogus keys that wouldn't be used

--HG--
branch : fuzz
This commit is contained in:
Matt Johnston 2018-02-21 21:49:24 +08:00
parent dbc0520992
commit 05f4e29a52
2 changed files with 24 additions and 2 deletions
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2
fuzz-common.c
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@ -22,6 +22,8 @@ void fuzz_common_setup(void) {
fuzz.input = m_malloc(sizeof(buffer));
_dropbear_log = fuzz_dropbear_log;
crypto_init();
/* let any messages get flushed */
setlinebuf(stdout);
}
int fuzz_set_input(const uint8_t *Data, size_t Size) {

24
fuzzer-verify.c
View File

@ -29,8 +29,28 @@ int LLVMFuzzerTestOneInput(const uint8_t *Data, size_t Size) {
sign_key *key = new_sign_key();
enum signkey_type type = DROPBEAR_SIGNKEY_ANY;
if (buf_get_pub_key(fuzz.input, key, &type) == DROPBEAR_SUCCESS) {
/* Don't expect random fuzz input to verify */
assert(buf_verify(fuzz.input, key, verifydata) == DROPBEAR_FAILURE);
if (buf_verify(fuzz.input, key, verifydata) == DROPBEAR_SUCCESS) {
/* The fuzzer is capable of generating keys with a signature to match.
We don't want false positives if the key is bogus, since a client/server
wouldn't be trusting a bogus key anyway */
int boguskey = 0;
if (type == DROPBEAR_SIGNKEY_DSS) {
/* So far have seen dss keys with bad p/q/g domain parameters */
int pprime, qprime;
assert(mp_prime_is_prime(key->dsskey->p, 5, &pprime) == MP_OKAY);
assert(mp_prime_is_prime(key->dsskey->q, 18, &qprime) == MP_OKAY);
boguskey = !(pprime && qprime);
/* Could also check g**q mod p == 1 */
}
if (!boguskey) {
printf("Random key/signature managed to verify!\n");
abort();
}
}
}
sign_key_free(key);
m_malloc_free_epoch(1, 0);