Merge branch 'mptcp-misc-fixes-involving-fallback-to-tcp'

Matthieu Baerts says:

====================
mptcp: misc. fixes involving fallback to TCP

- Patch 1: better handle DSS corruptions from a bugged peer: reducing
  warnings, doing a fallback or a reset depending on the subflow state.
  For >= v5.7.

- Patch 2: fix DSS corruption due to large pmtu xmit, where MPTCP was
  not taken into account. For >= v5.6.

- Patch 3: fallback when MPTCP opts are dropped after the first data
  packet, instead of resetting the connection. For >= v5.6.

- Patch 4: restrict the removal of a subflow to other closing states, a
  better fix, for a recent one. For >= v5.10.
====================

Link: https://patch.msgid.link/20241008-net-mptcp-fallback-fixes-v1-0-c6fb8e93e551@kernel.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

1 files changed, 21 insertions, 3 deletions

diff --git a/net/mptcp/protocol.c b/net/mptcp/protocol.c
index c2317919fc14..6d0e201c3eb2 100644
--- a/net/mptcp/protocol.c
+++ b/net/mptcp/protocol.c
@@ -620,6 +620,18 @@ static bool mptcp_check_data_fin(struct sock *sk)
 	return ret;
 }
 
+static void mptcp_dss_corruption(struct mptcp_sock *msk, struct sock *ssk)
+{
+	if (READ_ONCE(msk->allow_infinite_fallback)) {
+		MPTCP_INC_STATS(sock_net(ssk),
+				MPTCP_MIB_DSSCORRUPTIONFALLBACK);
+		mptcp_do_fallback(ssk);
+	} else {
+		MPTCP_INC_STATS(sock_net(ssk), MPTCP_MIB_DSSCORRUPTIONRESET);
+		mptcp_subflow_reset(ssk);
+	}
+}
+
 static bool __mptcp_move_skbs_from_subflow(struct mptcp_sock *msk,
 					   struct sock *ssk,
 					   unsigned int *bytes)
@@ -692,10 +704,16 @@ static bool __mptcp_move_skbs_from_subflow(struct mptcp_sock *msk,
 				moved += len;
 			seq += len;
 
-			if (WARN_ON_ONCE(map_remaining < len))
-				break;
+			if (unlikely(map_remaining < len)) {
+				DEBUG_NET_WARN_ON_ONCE(1);
+				mptcp_dss_corruption(msk, ssk);
+			}
 		} else {
-			WARN_ON_ONCE(!fin);
+			if (unlikely(!fin)) {
+				DEBUG_NET_WARN_ON_ONCE(1);
+				mptcp_dss_corruption(msk, ssk);
+			}
+
 			sk_eat_skb(ssk, skb);
 			done = true;
 		}