Re: [PATCH] mptcp: fix KMSAN: uninit-value in mptcp_established_options

[Matthieu Baerts <matttbe@kernel.org>]

Hello,

On 04/05/2026 11:51, Matthieu Baerts (NGI0) wrote:
> Just to let syzbot testing it.

Sorry for the noise: I forgot to add the syzbot instruction... (and I
forgot to remove the MPTCP ML from the sendmail.to option).

Hopefully now the following is correct:
#syz test

diff --git a/net/mptcp/options.c b/net/mptcp/options.c
index 8a1c5698983c..24903a12a4e0 100644
--- a/net/mptcp/options.c
+++ b/net/mptcp/options.c
@@ -583,6 +583,8 @@ static bool mptcp_established_options_dss(struct sock *sk, struct sk_buff *skb,
 				map_size += TCPOLEN_MPTCP_DSS_CHECKSUM;
 
 			opts->ext_copy = *mpext;
+		} else {
+			opts->ext_copy.use_map = 0;
 		}
 
 		dss_size = map_size;