From ebfcf58dc7937c779c063b208c524445450d4c42 Mon Sep 17 00:00:00 2001
From: Gilles Peskine <Gilles.Peskine@arm.com>
Date: Wed, 20 Mar 2024 17:51:48 +0100
Subject: [PATCH] Always list TLS-RSA-WITH-NULL-SHA256, but skip conditionally
 with GnuTLS

TLS-RSA-WITH-NULL-SHA256 is officially a cipher suite only since TLS 1.2,
but Mbed TLS allows it in 1.0/1.1, and so did ancient versions of GnuTLS.
This script was only considering it for GnuTLS interoperability if the
running version of GnuTLS supported it with older protocol versions.

Change to always considering it, and in particular always including it with
--list-test-cases, but skipping it at runtime if GnuTLS doesn't support it.

Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>
---
 tests/compat.sh | 50 +++++++++++++++++++++++++++++++++++--------------
 1 file changed, 36 insertions(+), 14 deletions(-)

diff --git a/tests/compat.sh b/tests/compat.sh
index 92fcce39f..e41489f7b 100755
--- a/tests/compat.sh
+++ b/tests/compat.sh
@@ -640,24 +640,14 @@ add_gnutls_ciphersuites()
             ;;
 
         "RSA")
-            # TLS-RSA-WITH-NULL-SHA256 is a (D)TLS 1.2-only cipher suite,
-            # like all SHA256 cipher suites. But Mbed TLS supports it with
-            # (D)TLS 1.0 and 1.1 as well. So do ancient versions of GnuTLS,
-            # but this was considered a bug which was fixed in GnuTLS 3.4.7.
-            # Check the GnuTLS support list to see what the protocol version
-            # requirement is for that cipher suite.
-            if [ `minor_ver "$MODE"` -ge 3 ] || {
-                   [ `minor_ver "$MODE"` -gt 0 ] &&
-                   $GNUTLS_CLI --list | grep -q '^TLS_RSA_NULL_SHA256.*0$'
-               }
-            then
-                M_CIPHERS="$M_CIPHERS                           \
+            # Not actually supported with all GnuTLS versions. See
+            # GNUTLS_HAS_TLS1_RSA_NULL_SHA256= below.
+            M_CIPHERS="$M_CIPHERS                               \
                     TLS-RSA-WITH-NULL-SHA256                    \
                     "
-                G_CIPHERS="$G_CIPHERS                           \
+            G_CIPHERS="$G_CIPHERS                               \
                     +RSA:+NULL:+SHA256                          \
                     "
-            fi
             if [ `minor_ver "$MODE"` -ge 3 ]
             then
                 M_CIPHERS="$M_CIPHERS                           \
@@ -929,6 +919,23 @@ o_check_ciphersuite()
     fi
 }
 
+# g_check_ciphersuite CIPHER_SUITE_NAME
+g_check_ciphersuite()
+{
+    set -x
+    if [ -z "$GNUTLS_HAS_TLS1_RSA_NULL_SHA256" ]; then
+        case "$MODE" in
+            tls1|tls1_1|dtls1)
+                case "$1" in
+                    TLS-RSA-WITH-NULL-SHA256|+RSA:+NULL:+SHA256)
+                        SKIP_NEXT="YES";;
+                esac;;
+        esac
+    fi
+    set +x
+}
+
+
 setup_arguments()
 {
     O_MODE=""
@@ -1415,6 +1422,19 @@ for PEER in $PEERS; do
     esac
 done
 
+case " $PEERS " in *\ [Gg]nu*)
+    GNUTLS_HAS_TLS1_RSA_NULL_SHA256=
+    # TLS-RSA-WITH-NULL-SHA256 is a (D)TLS 1.2-only cipher suite,
+    # like all SHA256 cipher suites. But Mbed TLS supports it with
+    # (D)TLS 1.0 and 1.1 as well. So do ancient versions of GnuTLS,
+    # but this was considered a bug which was fixed in GnuTLS 3.4.7.
+    # Check the GnuTLS support list to see what the protocol version
+    # requirement is for that cipher suite.
+    if $GNUTLS_CLI --list | grep -q '^TLS_RSA_NULL_SHA256.*0$'; then
+        GNUTLS_HAS_TLS1_RSA_NULL_SHA256=YES
+    fi
+esac
+
 # Pick a "unique" port in the range 10000-19999.
 PORT="0000$$"
 PORT="1$(echo $PORT | tail -c 5)"
@@ -1504,6 +1524,7 @@ for MODE in $MODES; do
                     if [ "X" != "X$M_CIPHERS" ]; then
                         start_server "GnuTLS"
                         for i in $M_CIPHERS; do
+                            g_check_ciphersuite "$i"
                             run_client mbedTLS $i
                         done
                         stop_server
@@ -1512,6 +1533,7 @@ for MODE in $MODES; do
                     if [ "X" != "X$G_CIPHERS" ]; then
                         start_server "mbedTLS"
                         for i in $G_CIPHERS; do
+                            g_check_ciphersuite "$i"
                             run_client GnuTLS $i
                         done
                         stop_server