From c149dd0767f32789e391280cb1eb06b7eb7c6bce Mon Sep 17 00:00:00 2001

From: Alexander Sosedkin <asosedkin@redhat.com>

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 <asosedkin@redhat.com>

Signed-off-by: Hubert Kario <hkario@redhat.com>

Tested-by: Hubert Kario <hkario@redhat.com>

---

 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 <hkario@redhat.com>

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 <hkario@redhat.com>

---

 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