[PATCH 6.18 079/122] mptcp: only reset subflow errors when propagated

Greg Kroah-Hartman
2026-02-04T15:32:20Z

From: Matthieu Baerts (NGI0) <matttbe@kernel.org>

commit dccf46179ddd6c04c14be8ed584dc54665f53f0e upstream.

Some subflow socket errors need to be reported to the MPTCP socket: the
initial subflow connect (MP_CAPABLE), and the ones from the fallback
sockets. The others are not propagated.

The issue is that sock_error() was used to retrieve the error, which was
also resetting the sk_err field. Because of that, when notifying the
userspace about subflow close events later on from the MPTCP worker, the
ssk->sk_err field was always 0.

Now, the error (sk_err) is only reset when propagating it to the msk.

Fixes: 15cc10453398 ("mptcp: deliver ssk errors to msk")
Cc: stable@vger.kernel.org
Reviewed-by: Geliang Tang <geliang@kernel.org>
Signed-off-by: Matthieu Baerts (NGI0) <matttbe@kernel.org>
Link: https://patch.msgid.link/20260127-net-mptcp-dup-nl-events-v1-3-7f71e1bc4feb@kernel.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
net/mptcp/protocol.c | 9 +++++----
1 file changed, 5 insertions(+), 4 deletions(-)

--- a/net/mptcp/protocol.c
+++ b/net/mptcp/protocol.c
@@ -784,11 +784,8 @@ static bool __mptcp_ofo_queue(struct mpt

static bool __mptcp_subflow_error_report(struct sock *sk, struct sock *ssk)
{
- int err = sock_error(ssk);
int ssk_state;
-
- if (!err)
- return false;
+ int err;

/* only propagate errors on fallen-back sockets or
* on MPC connect
@@ -796,6 +793,10 @@ static bool __mptcp_subflow_error_report
if (sk->sk_state != TCP_SYN_SENT && !__mptcp_check_fallback(mptcp_sk(sk)))
return false;

+ err = sock_error(ssk);
+ if (!err)
+ return false;
+
/* We need to propagate only transition to CLOSE state.
* Orphaned socket will see such state change via
* subflow_sched_work_if_closed() and that path will properly