From c149dd0767f32789e391280cb1eb06b7eb7c6bce Mon Sep 17 00:00:00 2001 From: Alexander Sosedkin Date: Tue, 9 Aug 2022 16:05:53 +0200 Subject: [PATCH 1/2] auth/rsa: side-step potential side-channel Remove branching that depends on secret data. Signed-off-by: Alexander Sosedkin Signed-off-by: Hubert Kario Tested-by: Hubert Kario --- lib/auth/rsa.c | 10 ---------- 1 file changed, 10 deletions(-) diff --git a/lib/auth/rsa.c b/lib/auth/rsa.c index 8108ee841d..6b158bacb2 100644 --- a/lib/auth/rsa.c +++ b/lib/auth/rsa.c @@ -155,7 +155,6 @@ static int proc_rsa_client_kx(gnutls_session_t session, uint8_t * data, size_t _data_size) { - const char attack_error[] = "auth_rsa: Possible PKCS #1 attack\n"; gnutls_datum_t ciphertext; int ret, dsize; ssize_t data_size = _data_size; @@ -235,15 +234,6 @@ proc_rsa_client_kx(gnutls_session_t session, uint8_t * data, ok &= CONSTCHECK_NOT_EQUAL(check_ver_min, 0) & CONSTCHECK_EQUAL(session->key.key.data[1], ver_min); - if (ok) { - /* call logging function unconditionally so all branches are - * indistinguishable for timing and cache access when debug - * logging is disabled */ - _gnutls_no_log("%s", attack_error); - } else { - _gnutls_debug_log("%s", attack_error); - } - /* This is here to avoid the version check attack * discussed above. */ -- 2.39.1 From 7c963102ec2119eecc1789b993aabe5edfd75f3b Mon Sep 17 00:00:00 2001 From: Hubert Kario Date: Wed, 8 Feb 2023 14:32:09 +0100 Subject: [PATCH 2/2] rsa: remove dead code since the `ok` variable isn't used any more, we can remove all code used to calculate it Signed-off-by: Hubert Kario --- lib/auth/rsa.c | 20 +++----------------- 1 file changed, 3 insertions(+), 17 deletions(-) diff --git a/lib/auth/rsa.c b/lib/auth/rsa.c index 6b158bacb2..858701fe6e 100644 --- a/lib/auth/rsa.c +++ b/lib/auth/rsa.c @@ -159,8 +159,6 @@ proc_rsa_client_kx(gnutls_session_t session, uint8_t * data, int ret, dsize; ssize_t data_size = _data_size; volatile uint8_t ver_maj, ver_min; - volatile uint8_t check_ver_min; - volatile uint32_t ok; #ifdef ENABLE_SSL3 if (get_num_version(session) == GNUTLS_SSL3) { @@ -186,7 +184,6 @@ proc_rsa_client_kx(gnutls_session_t session, uint8_t * data, ver_maj = _gnutls_get_adv_version_major(session); ver_min = _gnutls_get_adv_version_minor(session); - check_ver_min = (session->internals.allow_wrong_pms == 0); session->key.key.data = gnutls_malloc(GNUTLS_MASTER_SIZE); if (session->key.key.data == NULL) { @@ -205,10 +202,9 @@ proc_rsa_client_kx(gnutls_session_t session, uint8_t * data, return ret; } - ret = - gnutls_privkey_decrypt_data2(session->internals.selected_key, - 0, &ciphertext, session->key.key.data, - session->key.key.size); + gnutls_privkey_decrypt_data2(session->internals.selected_key, + 0, &ciphertext, session->key.key.data, + session->key.key.size); /* After this point, any conditional on failure that cause differences * in execution may create a timing or cache access pattern side * channel that can be used as an oracle, so treat very carefully */ @@ -224,16 +220,6 @@ proc_rsa_client_kx(gnutls_session_t session, uint8_t * data, * Vlastimil Klima, Ondej Pokorny and Tomas Rosa. */ - /* ok is 0 in case of error and 1 in case of success. */ - - /* if ret < 0 */ - ok = CONSTCHECK_EQUAL(ret, 0); - /* session->key.key.data[0] must equal ver_maj */ - ok &= CONSTCHECK_EQUAL(session->key.key.data[0], ver_maj); - /* if check_ver_min then session->key.key.data[1] must equal ver_min */ - ok &= CONSTCHECK_NOT_EQUAL(check_ver_min, 0) & - CONSTCHECK_EQUAL(session->key.key.data[1], ver_min); - /* This is here to avoid the version check attack * discussed above. */ -- 2.39.1