[openssl-dev] 1.0.2 regression with Cisco DTLS_BAD_VER

[John Foley]

Which Cisco product are you using, the ASA?  What version of software do
you have on the product?  While I can't speak for all Cisco products, I
can confirm that many Cisco products are using OpenSSL 1.0.1, which
implies support for DTLS 1.0. If you care to share more details, I can
try to engage the product team to better understand this.



On 02/16/2015 05:28 AM, David Woodhouse wrote:
> Commit 9cf0f187 in HEAD, and 68039af3 in 1.0.2, removed a version check
> from dtls1_buffer_message() which was needed to distinguish between DTLS
> 1.x and Cisco's pre-standard version of DTLS.
>
> $DEITY knows why Cisco haven't moved to the standard version of DTLS by
> now. The RFC was published in 2006, and since you can tell the
> difference on the wire it's *trivial* to have the server accept both and
> upgrade the clients piecemeal. The ocserv server manages this.
>
> But it isn't our place to marvel at Cisco's incompetence (like the fact
> that their DTLS implementation is still dropping out-of-order received
> packets, 6½ years after I fixed RT#1752). Our place is to try to be
> compatible with it. And this commit broke that, causing the OpenConnect
> VPN client to abort:
>
> Connected vpntest0 as 192.168.1.13, using SSL
> d1_both.c(1112): OpenSSL internal error, assertion failed: s->d1->w_msg_hdr.msg_len + DTLS1_CCS_HEADER_LENGTH == (unsigned int)s->init_num
> Aborted (core dumped)
>
> ---
> The patch below fixes it. Tested in 1.0.2, but I haven't tested with
> HEAD yet because I need to work out how to set up the DTLS session to be
> "resumed" — none of this compiles any more...
>
> ../dtls.c: In function 'start_dtls_handshake':
> ../dtls.c:141:24: error: dereferencing pointer to incomplete type
>    vpninfo->dtls_session->ssl_version = 0x0100; /* DTLS1_BAD_VER */
>                         ^
> ../dtls.c:145:23: error: dereferencing pointer to incomplete type
>   vpninfo->dtls_session->master_key_length = sizeof(vpninfo->dtls_secret);
>                        ^
> ../dtls.c:146:30: error: dereferencing pointer to incomplete type
>   memcpy(vpninfo->dtls_session->master_key, vpninfo->dtls_secret,
>                               ^
> ../dtls.c:149:23: error: dereferencing pointer to incomplete type
>   vpninfo->dtls_session->session_id_length = sizeof(vpninfo->dtls_session_id);
>                        ^
> ../dtls.c:150:30: error: dereferencing pointer to incomplete type
>   memcpy(vpninfo->dtls_session->session_id, vpninfo->dtls_session_id,
>                               ^
> ../dtls.c:170:23: error: dereferencing pointer to incomplete type
>   vpninfo->dtls_session->cipher = dtls_cipher;
>                        ^
> ../dtls.c:171:23: error: dereferencing pointer to incomplete type
>   vpninfo->dtls_session->cipher_id = dtls_cipher->id;
>                        ^
> ../dtls.c:171:48: error: dereferencing pointer to incomplete type
>   vpninfo->dtls_session->cipher_id = dtls_cipher->id;
>
> diff --git a/ssl/d1_both.c b/ssl/d1_both.c
> index 2553c3d..1116416 100644
> --- a/ssl/d1_both.c
> +++ b/ssl/d1_both.c
> @@ -1108,8 +1108,9 @@ int dtls1_buffer_message(SSL *s, int is_ccs)
>      memcpy(frag->fragment, s->init_buf->data, s->init_num);
>  
>      if (is_ccs) {
> +	/* For DTLS_BAD_VER the header length is non-standard */
>          OPENSSL_assert(s->d1->w_msg_hdr.msg_len +
> -                       DTLS1_CCS_HEADER_LENGTH == (unsigned int)s->init_num);
> +                       ((s->version==DTLS1_VERSION)?DTLS1_CCS_HEADER_LENGTH:3) == (unsigned int)s->init_num);
>      } else {
>          OPENSSL_assert(s->d1->w_msg_hdr.msg_len +
>                         DTLS1_HM_HEADER_LENGTH == (unsigned int)s->init_num);
>
>
>
>
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