From 2eaf2c79692abcfef2980c64ed5139efd5581736 Mon Sep 17 00:00:00 2001
From: Jaeden Amero <jaeden@patater.com>
Date: Wed, 5 Jun 2019 13:32:08 +0100
Subject: [PATCH] ssl: Don't access non-existent encrypt_then_mac field

When MBEDTLS_SSL_ENCRYPT_THEN_MAC is enabled, but not
MBEDTLS_SSL_SOME_MODES_USE_MAC, mbedtls_ssl_derive_keys() and
build_transforms() will attempt to use a non-existent `encrypt_then_mac`
field in the ssl_transform.

    Compile [ 93.7%]: ssl_tls.c
    [Error] ssl_tls.c@865,14: 'mbedtls_ssl_transform {aka struct mbedtls_ssl_transform}' ha
s no member named 'encrypt_then_mac'
    [ERROR] ./mbed-os/features/mbedtls/src/ssl_tls.c: In function 'mbedtls_ssl_derive_keys'
:
    ./mbed-os/features/mbedtls/src/ssl_tls.c:865:14: error: 'mbedtls_ssl_transform {aka str
uct mbedtls_ssl_transform}' has no member named 'encrypt_then_mac'
         transform->encrypt_then_mac = session->encrypt_then_mac;
                  ^~

Change mbedtls_ssl_derive_keys() and build_transforms() to only access
`encrypt_then_mac` if `encrypt_then_mac` is actually present. Fix any
unused variable warnings along the way, by additionally wrapping
function parameters with MBEDTLS_SSL_SOME_MODES_USE_MAC.

Add a regression test to detect when we have regressions with
configurations that do not include any MAC ciphersuites.

Fixes 92231325a765 ("Reduce size of `ssl_transform` if no MAC ciphersuite is enabled")
---
 library/ssl_tls.c                    |  7 ++++++-
 tests/scripts/all.sh                 | 14 ++++++++++++++
 tests/suites/test_suite_ssl.function |  3 ++-
 3 files changed, 22 insertions(+), 2 deletions(-)

diff --git a/library/ssl_tls.c b/library/ssl_tls.c
index b61453fe5..dc5202464 100644
--- a/library/ssl_tls.c
+++ b/library/ssl_tls.c
@@ -730,12 +730,14 @@ typedef int ssl_tls_prf_t(const unsigned char *, size_t, const char *,
 static int ssl_populate_transform( mbedtls_ssl_transform *transform,
                                    int ciphersuite,
                                    const unsigned char master[48],
+#if defined(MBEDTLS_SSL_SOME_MODES_USE_MAC)
 #if defined(MBEDTLS_SSL_ENCRYPT_THEN_MAC)
                                    int encrypt_then_mac,
 #endif
 #if defined(MBEDTLS_SSL_TRUNCATED_HMAC)
                                    int trunc_hmac,
 #endif
+#endif /* MBEDTLS_SSL_SOME_MODES_USE_MAC */
 #if defined(MBEDTLS_ZLIB_SUPPORT)
                                    int compression,
 #endif
@@ -766,7 +768,8 @@ static int ssl_populate_transform( mbedtls_ssl_transform *transform,
 #endif
 
     /* Copy info about negotiated version and extensions */
-#if defined(MBEDTLS_SSL_ENCRYPT_THEN_MAC)
+#if defined(MBEDTLS_SSL_ENCRYPT_THEN_MAC) && \
+    defined(MBEDTLS_SSL_SOME_MODES_USE_MAC)
     transform->encrypt_then_mac = encrypt_then_mac;
 #endif
     transform->minor_ver = minor_ver;
@@ -1327,12 +1330,14 @@ int mbedtls_ssl_derive_keys( mbedtls_ssl_context *ssl )
     ret = ssl_populate_transform( ssl->transform_negotiate,
                                   ssl->session_negotiate->ciphersuite,
                                   ssl->session_negotiate->master,
+#if defined(MBEDTLS_SSL_SOME_MODES_USE_MAC)
 #if defined(MBEDTLS_SSL_ENCRYPT_THEN_MAC)
                                   ssl->session_negotiate->encrypt_then_mac,
 #endif
 #if defined(MBEDTLS_SSL_TRUNCATED_HMAC)
                                   ssl->session_negotiate->trunc_hmac,
 #endif
+#endif /* MBEDTLS_SSL_SOME_MODES_USE_MAC */
 #if defined(MBEDTLS_ZLIB_SUPPORT)
                                   ssl->session_negotiate->compression,
 #endif
diff --git a/tests/scripts/all.sh b/tests/scripts/all.sh
index 9af040fba..3d94bc85d 100755
--- a/tests/scripts/all.sh
+++ b/tests/scripts/all.sh
@@ -883,6 +883,20 @@ component_test_no_max_fragment_length_small_ssl_out_content_len () {
     if_build_succeeded tests/ssl-opt.sh -f "Max fragment length\|Large buffer"
 }
 
+component_test_when_no_ciphersuites_have_mac () {
+    msg "build: when no ciphersuites have MAC"
+    scripts/config.pl unset MBEDTLS_CIPHER_NULL_CIPHER
+    scripts/config.pl unset MBEDTLS_ARC4_C
+    scripts/config.pl unset MBEDTLS_CIPHER_MODE_CBC
+    make
+
+    msg "test: !MBEDTLS_SSL_SOME_MODES_USE_MAC"
+    make test
+
+    msg "test ssl-opt.sh: !MBEDTLS_SSL_SOME_MODES_USE_MAC"
+    if_build_succeeded tests/ssl-opt.sh
+}
+
 component_test_null_entropy () {
     msg "build: default config with  MBEDTLS_TEST_NULL_ENTROPY (ASan build)"
     scripts/config.pl set MBEDTLS_TEST_NULL_ENTROPY
diff --git a/tests/suites/test_suite_ssl.function b/tests/suites/test_suite_ssl.function
index 65f585274..c6dd56452 100644
--- a/tests/suites/test_suite_ssl.function
+++ b/tests/suites/test_suite_ssl.function
@@ -159,7 +159,8 @@ static int build_transforms( mbedtls_ssl_transform *t_in,
      * Setup transforms
      */
 
-#if defined(MBEDTLS_SSL_ENCRYPT_THEN_MAC)
+#if defined(MBEDTLS_SSL_ENCRYPT_THEN_MAC) && \
+    defined(MBEDTLS_SSL_SOME_MODES_USE_MAC)
     t_out->encrypt_then_mac = etm;
     t_in->encrypt_then_mac = etm;
 #else