gnutls: fix CVE-2023-0361 timing side-channel in the TLS RSA key exchange code

Remove branching that depends on secret data.

since the `ok` variable isn't used any more, we can remove all code
used to calculate it

Signed-off-by: Vivek Kumbhar <vkumbhar@mvista.com>
Signed-off-by: Steve Sakoman <steve@sakoman.com>

2 files changed, 86 insertions, 0 deletions

diff --git a/meta/recipes-support/gnutls/gnutls/CVE-2023-0361.patch b/meta/recipes-support/gnutls/gnutls/CVE-2023-0361.patch
new file mode 100644
index 0000000000..943f4ca704
--- /dev/null
+++ b/meta/recipes-support/gnutls/gnutls/CVE-2023-0361.patch
@@ -0,0 +1,85 @@
+From 80a6ce8ddb02477cd724cd5b2944791aaddb702a Mon Sep 17 00:00:00 2001
+From: Alexander Sosedkin <asosedkin@redhat.com>
+Date: Tue, 9 Aug 2022 16:05:53 +0200
+Subject: [PATCH] auth/rsa: side-step potential side-channel
+
+Signed-off-by: Alexander Sosedkin <asosedkin@redhat.com>
+Signed-off-by: Hubert Kario <hkario@redhat.com>
+Tested-by: Hubert Kario <hkario@redhat.com>
+Upstream-Status: Backport [https://gitlab.com/gnutls/gnutls/-/commit/80a6ce8ddb02477cd724cd5b2944791aaddb702a
+                           https://gitlab.com/gnutls/gnutls/-/commit/4b7ff428291c7ed77c6d2635577c83a43bbae558]
+CVE: CVE-2023-0361
+Signed-off-by: Vivek Kumbhar <vkumbhar@mvista.com>
+---
+ lib/auth/rsa.c | 30 +++---------------------------
+ 1 file changed, 3 insertions(+), 27 deletions(-)
+
+diff --git a/lib/auth/rsa.c b/lib/auth/rsa.c
+index 8108ee8..858701f 100644
+--- a/lib/auth/rsa.c
++++ b/lib/auth/rsa.c
+@@ -155,13 +155,10 @@ 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;
+	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) {
+@@ -187,7 +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) {
+@@ -206,10 +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 */
+@@ -225,25 +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);
+-
+-	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.
+	 */
+--
+2.25.1
+
diff --git a/meta/recipes-support/gnutls/gnutls_3.6.14.bb b/meta/recipes-support/gnutls/gnutls_3.6.14.bb
index f1757871ce..0c3392d521 100644
--- a/meta/recipes-support/gnutls/gnutls_3.6.14.bb
+++ b/meta/recipes-support/gnutls/gnutls_3.6.14.bb
@@ -27,6 +27,7 @@ SRC_URI = "https://www.gnupg.org/ftp/gcrypt/gnutls/v${SHRT_VER}/gnutls-${PV}.tar
            file://CVE-2021-20232.patch \
            file://CVE-2022-2509.patch \
            file://CVE-2021-4209.patch \
+           file://CVE-2023-0361.patch \
 "
 
 SRC_URI[sha256sum] = "5630751adec7025b8ef955af4d141d00d252a985769f51b4059e5affa3d39d63"