Re-enable TLS version negotiation by default

Re-enable TLS version negotiation by default, so that users benefit from the stronger and better crypto of TLSv1.1 and TLSv1.2, without having to add 'tls-version-min' to their config files.

We tried this before in 2.3.3, but got various reports of people no longer being able to connect. Back then, we did not have a way for users to control the TLS version. We now have --tls-version-min and --tls-version-max, and even automatically set --tls-version-max to 1.1 if --cryptoapi is used, because the cryptoapi code is incompatible with TLS 1.2.

To make sure users can fall back to the _exact_ old default behaviour, not only limit the TLS version to 1.0 if --tls-version-max 1.0 is set, but also keep using the API calls TLSv1_{client,server}_method(), instead of the ones that support negotiation (SSLv23_{client,server}_method()). (Yes, the naming is awkward, but 'SSLv23' really means 'enable negotiation' in OpenSSL-API language.

This patch is for the release/2.3 branch only.

---
 src/openvpn/ssl_openssl.c | 20 ++++++++++----------
 1 file changed, 10 insertions(+), 10 deletions(-)

index 5207dfd..fd382fb 100644
@@ -121,15 +121,15 @@ tmp_rsa_cb (SSL * s, int is_export, int keylength)
 void
 tls_ctx_server_new(struct tls_root_ctx *ctx, unsigned int ssl_flags)
 {
-  const int tls_version_min =
-      (ssl_flags >> SSLF_TLS_VERSION_MIN_SHIFT) & SSLF_TLS_VERSION_MIN_MASK;
+  const int tls_version_max =
+      (ssl_flags >> SSLF_TLS_VERSION_MAX_SHIFT) & SSLF_TLS_VERSION_MAX_MASK;
 
   ASSERT(NULL != ctx);
 
-  if (tls_version_min > TLS_VER_UNSPEC)
-    ctx->ctx = SSL_CTX_new (SSLv23_server_method ());
-  else
+  if (tls_version_max == TLS_VER_1_0)
     ctx->ctx = SSL_CTX_new (TLSv1_server_method ());
+  else
+    ctx->ctx = SSL_CTX_new (SSLv23_server_method ());
 
   if (ctx->ctx == NULL)
     msg (M_SSLERR, "SSL_CTX_new SSLv23_server_method");

@@ -140,15 +140,15 @@ tls_ctx_server_new(struct tls_root_ctx *ctx, unsigned int ssl_flags)
 void
 tls_ctx_client_new(struct tls_root_ctx *ctx, unsigned int ssl_flags)
 {
-  const int tls_version_min =
-      (ssl_flags >> SSLF_TLS_VERSION_MIN_SHIFT) & SSLF_TLS_VERSION_MIN_MASK;
+  const int tls_version_max =
+      (ssl_flags >> SSLF_TLS_VERSION_MAX_SHIFT) & SSLF_TLS_VERSION_MAX_MASK;
 
   ASSERT(NULL != ctx);
 
-  if (tls_version_min > TLS_VER_UNSPEC)
-    ctx->ctx = SSL_CTX_new (SSLv23_client_method ());
-  else
+  if (tls_version_max == TLS_VER_1_0)
     ctx->ctx = SSL_CTX_new (TLSv1_client_method ());
+  else
+    ctx->ctx = SSL_CTX_new (SSLv23_client_method ());
 
   if (ctx->ctx == NULL)
     msg (M_SSLERR, "SSL_CTX_new SSLv23_client_method");

2.1.0

Am 10.03.2015 um 20:26 schrieb Steffan Karger:

conditional ACK, provided that:
a) the manual page is adjusted properly (I have sent a proposal in a separate message that is an incremental Git patch on top of Steffan's)
b) the release notes mention the --tls-version-max 1.0 workaround.

I don't see why we need the workaround, but I subscribe to due diligence, and caution.

Your patch has been applied to the release/2.3 branch.

commit 8dc6ed28941cb9b9167e0b466e96b5f11359eb59

Author: Steffan Karger
Date:   Tue Mar 10 20:26:45 2015 +0100

     Re-enable TLS version negotiation by default

     Signed-off-by: Steffan Karger <[email protected]...>
     Acked-by: Matthias Andree <[email protected]...>
     Message-Id: <[email protected]...>
     URL: http://article.gmane.org/gmane.network.openvpn.devel/9542
     Signed-off-by: Gert Doering <[email protected]...>

--
kind regards,

Gert Doering