[PATCH 2/5] lwip: tls: enforce checking of server certificates based on CA availability

[Jerome Forissier]

Instead of relying on some build time configuration to determine if
server certificates need to be checked against CA certificates, do it
based on the availability of such certificates. If no CA is configured
then no check can succeed; on the other hand if we have CA certs then
we should not ignore them. It is always possible to remove the CA certs
(via 'wget cacert 0 0') to force an HTTPS download that would fail
certificate validation.

Signed-off-by: Jerome Forissier <jerome.forissier at linaro.org>
---
 lib/lwip/lwip/src/apps/altcp_tls/altcp_tls_mbedtls.c        | 3 ++-
 .../lwip/src/include/lwip/apps/altcp_tls_mbedtls_opts.h     | 6 ------
 2 files changed, 2 insertions(+), 7 deletions(-)

diff --git a/lib/lwip/lwip/src/apps/altcp_tls/altcp_tls_mbedtls.c b/lib/lwip/lwip/src/apps/altcp_tls/altcp_tls_mbedtls.c
index 46421588fef..fa3d1d74fed 100644
--- a/lib/lwip/lwip/src/apps/altcp_tls/altcp_tls_mbedtls.c
+++ b/lib/lwip/lwip/src/apps/altcp_tls/altcp_tls_mbedtls.c
@@ -786,6 +786,7 @@ altcp_tls_create_config(int is_server, u8_t cert_count, u8_t pkey_count, int hav
   int ret;
   struct altcp_tls_config *conf;
   mbedtls_x509_crt *mem;
+  int authmode = have_ca ? MBEDTLS_SSL_VERIFY_REQUIRED : MBEDTLS_SSL_VERIFY_NONE;
 
   if (TCP_WND < MBEDTLS_SSL_IN_CONTENT_LEN || TCP_WND < MBEDTLS_SSL_OUT_CONTENT_LEN) {
     LWIP_DEBUGF(ALTCP_MBEDTLS_DEBUG|LWIP_DBG_LEVEL_SERIOUS,
@@ -840,7 +841,7 @@ altcp_tls_create_config(int is_server, u8_t cert_count, u8_t pkey_count, int hav
     altcp_mbedtls_free_config(conf);
     return NULL;
   }
-  mbedtls_ssl_conf_authmode(&conf->conf, ALTCP_MBEDTLS_AUTHMODE);
+  mbedtls_ssl_conf_authmode(&conf->conf, authmode);
 
   mbedtls_ssl_conf_rng(&conf->conf, mbedtls_ctr_drbg_random, &altcp_tls_entropy_rng->ctr_drbg);
 #if ALTCP_MBEDTLS_LIB_DEBUG != LWIP_DBG_OFF
diff --git a/lib/lwip/lwip/src/include/lwip/apps/altcp_tls_mbedtls_opts.h b/lib/lwip/lwip/src/include/lwip/apps/altcp_tls_mbedtls_opts.h
index e41301c061c..71aa5993935 100644
--- a/lib/lwip/lwip/src/include/lwip/apps/altcp_tls_mbedtls_opts.h
+++ b/lib/lwip/lwip/src/include/lwip/apps/altcp_tls_mbedtls_opts.h
@@ -100,12 +100,6 @@
 #define ALTCP_MBEDTLS_SESSION_TICKET_TIMEOUT_SECONDS  (60 * 60 * 24)
 #endif
 
-/** Certificate verification mode: MBEDTLS_SSL_VERIFY_NONE, MBEDTLS_SSL_VERIFY_OPTIONAL (default),
- * MBEDTLS_SSL_VERIFY_REQUIRED (recommended)*/
-#ifndef ALTCP_MBEDTLS_AUTHMODE
-#define ALTCP_MBEDTLS_AUTHMODE                        MBEDTLS_SSL_VERIFY_OPTIONAL
-#endif
-
 #endif /* LWIP_ALTCP */
 
 #endif /* LWIP_HDR_ALTCP_TLS_OPTS_H */
-- 
2.43.0