[PATCH 7.1 010/228] mptcp: options: reset DSS fields in case of unexpected size

7.1-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Matthieu Baerts (NGI0) <[email protected]>

commit 35772b4981f38ba8059372cde8753e8e477e98ec upstream.

A remote peer could send a malformed DSS with a wrong size, followed by
another DSS or MPC + Data. In this case, the first suboption will be
ignored, but leaving some fields written, which could lead to
inconsistency or access uninitialized data.

Explicitly reset the fields that could have been modified in case of
unexpected size.

Link: https://netdev-ai.bots.linux.dev/sashiko/#/patchset/20260728-net-mptcp-misc-fixes-7-2-rc6-v1-0-f7e2d229159d%40kernel.org?part=1
Fixes: 648ef4b88673 ("mptcp: Implement MPTCP receive path")
Cc: [email protected]
Signed-off-by: Matthieu Baerts (NGI0) <[email protected]>
Link: https://patch.msgid.link/20260803-net-mptcp-misc-fixes-7-2-rc6-v2-1-b8f496d71664@kernel.org
Signed-off-by: Jakub Kicinski <[email protected]>
Signed-off-by: Greg Kroah-Hartman <[email protected]>
---
 net/mptcp/options.c |    8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

--- a/net/mptcp/options.c
+++ b/net/mptcp/options.c
@@ -209,8 +209,14 @@ static void mptcp_parse_option(const str
 		 * RFC 8684 Section 3.3.0 checks later in subflow_data_ready
 		 */
 		if (opsize != expected_opsize &&
-		    opsize != expected_opsize + TCPOLEN_MPTCP_DSS_CHECKSUM)
+		    opsize != expected_opsize + TCPOLEN_MPTCP_DSS_CHECKSUM) {
+			mp_opt->dsn64 = 0;
+			mp_opt->use_map = 0;
+			mp_opt->ack64 = 0;
+			mp_opt->use_ack = 0;
+			mp_opt->data_fin = 0;
 			break;
+		}
 
 		mp_opt->suboptions |= OPTION_MPTCP_DSS;
 		if (mp_opt->use_ack) {