net/handshake: Enable the SNI extension to work properly

Enable the upper layer protocol to specify the SNI peername. This
avoids the need for tlshd to use a DNS lookup, which can return a
hostname that doesn't match the incoming certificate's SubjectName.

Fixes: 2fd5532044 ("net/handshake: Add a kernel API for requesting a TLSv1.3 handshake")
Reviewed-by: Simon Horman <simon.horman@corigine.com>
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

Documentation/netlink/specs/handshake.yaml

@@ -68,6 +68,9 @@ attribute-sets:
         type: nest
         nested-attributes: x509
         multi-attr: true
+      -
+        name: peername
+        type: string
   -
     name: done
     attributes:
@@ -105,6 +108,7 @@ operations:
             - auth-mode
             - peer-identity
             - certificate
+            - peername
     -
       name: done
       doc: Handler reports handshake completion

Documentation/networking/tls-handshake.rst

@@ -53,6 +53,7 @@ fills in a structure that contains the parameters of the request:
         struct socket   *ta_sock;
         tls_done_func_t ta_done;
         void            *ta_data;
+        const char      *ta_peername;
         unsigned int    ta_timeout_ms;
         key_serial_t    ta_keyring;
         key_serial_t    ta_my_cert;
@@ -71,6 +72,10 @@ instantiated a struct file in sock->file.
 has completed. Further explanation of this function is in the "Handshake
 Completion" sesction below.
 
+The consumer can provide a NUL-terminated hostname in the @ta_peername
+field that is sent as part of ClientHello. If no peername is provided,
+the DNS hostname associated with the server's IP address is used instead.
+
 The consumer can fill in the @ta_timeout_ms field to force the servicing
 handshake agent to exit after a number of milliseconds. This enables the
 socket to be fully closed once both the kernel and the handshake agent

include/net/handshake.h

@@ -24,6 +24,7 @@ struct tls_handshake_args {
 	struct socket		*ta_sock;
 	tls_done_func_t		ta_done;
 	void			*ta_data;
+	const char		*ta_peername;
 	unsigned int		ta_timeout_ms;
 	key_serial_t		ta_keyring;
 	key_serial_t		ta_my_cert;

include/uapi/linux/handshake.h

@@ -44,6 +44,7 @@ enum {
 	HANDSHAKE_A_ACCEPT_AUTH_MODE,
 	HANDSHAKE_A_ACCEPT_PEER_IDENTITY,
 	HANDSHAKE_A_ACCEPT_CERTIFICATE,
+	HANDSHAKE_A_ACCEPT_PEERNAME,
 
 	__HANDSHAKE_A_ACCEPT_MAX,
 	HANDSHAKE_A_ACCEPT_MAX = (__HANDSHAKE_A_ACCEPT_MAX - 1)

net/handshake/tlshd.c

@@ -31,6 +31,7 @@ struct tls_handshake_req {
 	int			th_type;
 	unsigned int		th_timeout_ms;
 	int			th_auth_mode;
+	const char		*th_peername;
 	key_serial_t		th_keyring;
 	key_serial_t		th_certificate;
 	key_serial_t		th_privkey;
@@ -48,6 +49,7 @@ tls_handshake_req_init(struct handshake_req *req,
 	treq->th_timeout_ms = args->ta_timeout_ms;
 	treq->th_consumer_done = args->ta_done;
 	treq->th_consumer_data = args->ta_data;
+	treq->th_peername = args->ta_peername;
 	treq->th_keyring = args->ta_keyring;
 	treq->th_num_peerids = 0;
 	treq->th_certificate = TLS_NO_CERT;
@@ -214,6 +216,12 @@ static int tls_handshake_accept(struct handshake_req *req,
 	ret = nla_put_u32(msg, HANDSHAKE_A_ACCEPT_MESSAGE_TYPE, treq->th_type);
 	if (ret < 0)
 		goto out_cancel;
+	if (treq->th_peername) {
+		ret = nla_put_string(msg, HANDSHAKE_A_ACCEPT_PEERNAME,
+				     treq->th_peername);
+		if (ret < 0)
+			goto out_cancel;
+	}
 	if (treq->th_timeout_ms) {
 		ret = nla_put_u32(msg, HANDSHAKE_A_ACCEPT_TIMEOUT, treq->th_timeout_ms);
 		if (ret < 0)