Preparing openvpn3 packaging for review - openssl challenges

[David Sommerseth]

Hi,

I'm running rpmlint against packages built based on the Fedora Copr [1] build
I've provided for some time.  I'm planning to move this forward for the standard
Fedora and EPEL repositories.  But rpmlint complains about the usage of
SSL_CTX_set_cipher_list(), which I in this case would call a false-positive
for OpenVPN.

[1] https://copr.fedorainfracloud.org/coprs/dsommers/openvpn3/
    https://gitlab.com/dazo/copr-openvpn3

The code which trips this warning is:

-------------------------------------------------------------------------------
          if (config->force_aes_cbc_ciphersuites)
            {
              if (!SSL_CTX_set_cipher_list(ctx, "DHE-RSA-AES256-SHA:DHE-RSA-AES128-SHA"))
                OPENVPN_THROW(ssl_context_error, "OpenSSLContext: SSL_CTX_set_cipher_list failed for force_aes_cbc_ciphersuites");
            }
          else
            {
              if (!SSL_CTX_set_cipher_list(ctx,
                                           /* default list as a basis */
                                           "DEFAULT"
                                           /* Disable export ciphers, low and medium */
                                           ":!EXP:!LOW:!MEDIUM"
                                           /* Disable static (EC)DH keys (no forward secrecy) */
                                           ":!kDH:!kECDH"
                                           /* Disable DSA private keys */
                                           ":!DSS"
                                           /* Disable RC4 cipher */
                                           ":!RC4"
                                           /* Disable MD5 */
                                           ":!MD5"
                                           /* Disable unsupported TLS modes */
                                           ":!PSK:!SRP:!kRSA"
                                           /* Disable SSLv2 cipher suites*/
                                           ":!SSLv2"
                                           ))
                  OPENVPN_THROW(ssl_context_error, "OpenSSLContext: SSL_CTX_set_cipher_list failed");
#if OPENSSL_VERSION_NUMBER >= 0x10002000L && OPENSSL_VERSION_NUMBER < 0x10100000L
              SSL_CTX_set_ecdh_auto(ctx, 1); // this method becomes a no-op in OpenSSL 1.1
#endif
            }
-------------------------------------------------------------------------------
These calls can be found in openvpn/openssl/ssl/sslctx.hpp
https://github.com/OpenVPN/openvpn3/blob/b62654274fd938ebb82dbe3a2e78d9b8fd465970/openvpn/openssl/ssl/sslctx.hpp#L1094

The first SSL_CTX_set_cipher_list() is being slate for removal, as the
"force_aes_cbc_ciphersuits" feature is not considered needed any more;
negotiation works much better nowadays than when this was added
about 5 years ago.  But the cipher-list here shouldn't be of that much
concern.

The second block should really be fine too, it just strictly enforces a fairly
strict default set of ciphers.

So my question is if this will be a show-stopper for getting the openvpn3
package into the standard Fedora + EPEL repositories?

--
kind regards,

David Sommerseth
OpenVPN Inc

[Tomas Mraz]

On Tue, 2020-02-18 at 21:16 +0100, David Sommerseth wrote:
> Hi,
>
> I'm running rpmlint against packages built based on the Fedora Copr
> [1] build
> I've provided for some time.  I'm planning to move this forward for
> the standard
> Fedora and EPEL repositories.  But rpmlint complains about the usage
> of
> SSL_CTX_set_cipher_list(), which I in this case would call a false-
> positive
> for OpenVPN.
>
> [1] https://copr.fedorainfracloud.org/coprs/dsommers/openvpn3/
>     https://gitlab.com/dazo/copr-openvpn3
>
> The code which trips this warning is:
>       if (config->force_aes_cbc_ciphersuites)
>         {
>           if (!SSL_CTX_set_cipher_list(ctx, "DHE-RSA-AES256-
>
> SHA:DHE-RSA-AES128-SHA"))
>                 OPENVPN_THROW(ssl_context_error, "OpenSSLContext:
> SSL_CTX_set_cipher_list failed for force_aes_cbc_ciphersuites");
>             }
>           else
>             {
>               if (!SSL_CTX_set_cipher_list(ctx,
>                                            /* default list as a basis
> */
>                                            "DEFAULT"
>                                            /* Disable export ciphers,
> low and medium */
>                                            ":!EXP:!LOW:!MEDIUM"
>                                            /* Disable static (EC)DH
> keys (no forward secrecy) */
>                                            ":!kDH:!kECDH"
>                                            /* Disable DSA private
> keys */
>                                            ":!DSS"
>                                            /* Disable RC4 cipher */
>                                            ":!RC4"
>                                            /* Disable MD5 */
>                                            ":!MD5"
>                                            /* Disable unsupported TLS
> modes */
>                                            ":!PSK:!SRP:!kRSA"
>                                            /* Disable SSLv2 cipher
> suites*/
>                                            ":!SSLv2"
>                                            ))
>                   OPENVPN_THROW(ssl_context_error, "OpenSSLContext:
> SSL_CTX_set_cipher_list failed");
> #if OPENSSL_VERSION_NUMBER >= 0x10002000L && OPENSSL_VERSION_NUMBER <
> 0x10100000L
>               SSL_CTX_set_ecdh_auto(ctx, 1); // this method becomes a
> no-op in OpenSSL 1.1
> #endif
>             }
>
> These calls can be found in openvpn/openssl/ssl/sslctx.hpp
> <
> https://github.com/OpenVPN/openvpn3/blob/b62654274fd938ebb82dbe3a2e78d9b8fd4...
> >
>
> The first SSL_CTX_set_cipher_list() is being slate for removal, as
> the
> "force_aes_cbc_ciphersuits" feature is not considered needed any
> more;

As this would be non-default setting, it would be fine anyway.
> negotiation works much better nowadays than when this was added
> about 5 years ago.  But the cipher-list here shouldn't be of that
> much
> concern.
>
> The second block should really be fine too, it just strictly enforces
> a fairly
> strict default set of ciphers.

No, the second call is not correct. Basically there should be no call
to SSL_CTX_set_cipher_list() unless the user explicitly wants to
override the defaults. The default in Fedora is already sane and safe
and ensures the crypto policy is properly applied.
> So my question is if this will be a show-stopper for getting the
> openvpn3
> package into the standard Fedora + EPEL repositories?

Please just patch out the second call.