[RFH/PATCH] imap-send: support SNI (RFC4366)

[RFH/PATCH] imap-send: support SNI (RFC4366)

[Junio C Hamano]

To talk to a site that serves multiple names on a single IP address,
the client needs to ask for the specific hostname it wants to talk
to. Otherwise, the default certificate returned from the IP address
may not match that of the host we wanted to talk to.

Signed-off-by: Junio C Hamano <gitster@pobox.com>
---

 * I need help from people on this patch in two areas:

 (1) I only tested this patch by connecting to https://googlemail.com/ 
     with

     $ git -c imap.host=imaps://googlemail.com -c imap.port=443 imap-send <this-patch.txt

     as it is the only site I knew clients needs to talk SNI to get
     the right certificate to verify; of course the port does not
     talk imap, and the only thing that is tested by that approach is
     we successfully establish an SSL/TLS connection.  Without the
     patch, we fail to verify the certificate (we get a cert that is
     for another hostname that is hosted at the same IP address), and
     with the patch, we successfully get the right one.

     I would appreciate it if somebody knows an imap server that
     needs SNI and runs an end-to-end test against that server.

 (2) I do not know if everybody has SSL_set_tslext_host_name() macro
     defined, so this patch may be breaking build for people with
     different versions of OpenSSL.

 imap-send.c | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/imap-send.c b/imap-send.c
index 171c887..d9abd8b 100644
--- a/imap-send.c
+++ b/imap-send.c
@@ -370,6 +370,15 @@ static int ssl_socket_connect(struct imap_socket *sock, int use_tls_only, int ve
 		return -1;
 	}
 
+	/*
+	 * SNI (RFC4366)
+	 * OpenSSL does not document this function, but the implementation
+	 * returns 1 on success, 0 on failure after calling SSLerr().
+	 */
+	ret = SSL_set_tlsext_host_name(sock->ssl, server.host);
+	if (ret != 1)
+		warning("SSL_set_tslext_host_name(%s) failed.\n", server.host);
+
 	ret = SSL_connect(sock->ssl);
 	if (ret <= 0) {
 		socket_perror("SSL_connect", sock, ret);
-- 
1.8.2.rc0.106.ga6e4a61

Re: [RFH/PATCH] imap-send: support SNI (RFC4366)

[Junio C Hamano]

Junio C Hamano <gitster@pobox.com> writes:

> To talk to a site that serves multiple names on a single IP address,
> the client needs to ask for the specific hostname it wants to talk
> to. Otherwise, the default certificate returned from the IP address
> may not match that of the host we wanted to talk to.
>
> Signed-off-by: Junio C Hamano <gitster@pobox.com>
> ---
>
>  * I need help from people on this patch in two areas:
>
>  (1) I only tested this patch by connecting to https://googlemail.com/ 
>      with
> ...
>      I would appreciate it if somebody knows an imap server that
>      needs SNI and runs an end-to-end test against that server.
> 
>  (2) I do not know if everybody has SSL_set_tslext_host_name() macro
>      defined, so this patch may be breaking build for people with
>      different versions of OpenSSL.

What I queued for tonight replaces the posted patch with this
version in order to address (2) above.

-- >8 --
Subject: [PATCH] imap-send: support SNI (RFC4366)

To talk with some sites that serve multiple names on a single IP
address, the client needs to ask for the specific host it wants to
talk to.

Signed-off-by: Junio C Hamano <gitster@pobox.com>
---
 imap-send.c | 11 +++++++++++
 1 file changed, 11 insertions(+)

diff --git a/imap-send.c b/imap-send.c
index 171c887..ab2098a 100644
--- a/imap-send.c
+++ b/imap-send.c
@@ -370,6 +370,17 @@ static int ssl_socket_connect(struct imap_socket *sock, int use_tls_only, int ve
 		return -1;
 	}
 
+#ifdef SSL_CTRL_SET_TLSEXT_HOSTNAME
+	/*
+	 * SNI (RFC4366)
+	 * OpenSSL does not document this function, but the implementation
+	 * returns 1 on success, 0 on failure after calling SSLerr().
+	 */
+	ret = SSL_set_tlsext_host_name(sock->ssl, server.host);
+	if (ret != 1)
+		warning("SSL_set_tslext_host_name(%s) failed.\n", server.host);
+#endif
+
 	ret = SSL_connect(sock->ssl);
 	if (ret <= 0) {
 		socket_perror("SSL_connect", sock, ret);
-- 
1.8.2.rc0.127.g4d5d7da

Re: [RFH/PATCH] imap-send: support SNI (RFC4366)

[Jeff King]

On Wed, Feb 20, 2013 at 09:35:16PM -0800, Junio C Hamano wrote:

>>  (2) I do not know if everybody has SSL_set_tslext_host_name() macro
>>      defined, so this patch may be breaking build for people with
>>      different versions of OpenSSL.
> [...]
>
> +#ifdef SSL_CTRL_SET_TLSEXT_HOSTNAME
> +	/*
> +	 * SNI (RFC4366)
> +	 * OpenSSL does not document this function, but the implementation
> +	 * returns 1 on success, 0 on failure after calling SSLerr().
> +	 */
> +	ret = SSL_set_tlsext_host_name(sock->ssl, server.host);
> +	if (ret != 1)
> +		warning("SSL_set_tslext_host_name(%s) failed.\n", server.host);
> +#endif

Yes, I think this is the right macro to check. According to OpenSSL's
CHANGES file, it was introduced between 0.9.8n and 1.0.0 (Mar 2010). But
I note that the use of the same macro in libcurl dates to 2008. Curious.

Note that you have a typo in your warning text (tslext) and an
extra newline.

As far as testing goes, I don't have an SNI IMAP server handy, but I
think you can simulate one with "openssl s_server". It may be a good
long-term goal to test any ssl-specific code against that in our test
suite (on the other hand, most of the interesting stuff is https, where
the details are all handled by curl).

-Peff