From 35772b4981f38ba8059372cde8753e8e477e98ec Mon Sep 17 00:00:00 2001 From: "Matthieu Baerts (NGI0)" Date: Mon, 3 Aug 2026 18:16:33 +0200 Subject: [PATCH] mptcp: options: reset DSS fields in case of unexpected size 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: stable@vger.kernel.org Signed-off-by: Matthieu Baerts (NGI0) Link: https://patch.msgid.link/20260803-net-mptcp-misc-fixes-7-2-rc6-v2-1-b8f496d71664@kernel.org Signed-off-by: Jakub Kicinski --- net/mptcp/options.c | 8 +++++++- 1 file changed, 7 insertions(+), 1 deletion(-) diff --git a/net/mptcp/options.c b/net/mptcp/options.c index c664023d37ba..038eca33c6b1 100644 --- a/net/mptcp/options.c +++ b/net/mptcp/options.c @@ -188,8 +188,14 @@ static void mptcp_parse_option(const struct sk_buff *skb, * 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) {