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

(From OE-Core rev: 5b8a3601ebff7a0cdfaa50d7a0b5e384a7e2514c)

Signed-off-by: Vivek Kumbhar <vkumbhar@mvista.com>
Signed-off-by: Steve Sakoman <steve@sakoman.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

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"