Merge branch 'mptcp-misc-fixes'

Matthieu Baerts says:

====================
mptcp: misc. fixes

Here are two unrelated fixes, plus an extra patch:

- Patch 1: prevent a warning by removing an unneeded and incorrect small
  optimisation in the path-manager. A fix for v5.10.

- Patch 2: reset a subflow when MPTCP opts have been dropped after
  having correctly added a new path. A fix for v5.19.

- Patch 3: add a safety check to prevent issues like the one fixed by
  the second patch.
====================

Link: https://patch.msgid.link/20250224-net-mptcp-misc-fixes-v1-0-f550f636b435@kernel.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

3 files changed, 3 insertions, 19 deletions

diff --git a/net/mptcp/pm_netlink.c b/net/mptcp/pm_netlink.c
index 572d160edca3..c0e47f4f7b1a 100644
--- a/net/mptcp/pm_netlink.c
+++ b/net/mptcp/pm_netlink.c
@@ -1514,11 +1514,6 @@ static int mptcp_nl_remove_subflow_and_signal_addr(struct net *net,
 		if (mptcp_pm_is_userspace(msk))
 			goto next;
 
-		if (list_empty(&msk->conn_list)) {
-			mptcp_pm_remove_anno_addr(msk, addr, false);
-			goto next;
-		}
-
 		lock_sock(sk);
 		remove_subflow = mptcp_lookup_subflow_by_saddr(&msk->conn_list, addr);
 		mptcp_pm_remove_anno_addr(msk, addr, remove_subflow &&
diff --git a/net/mptcp/protocol.h b/net/mptcp/protocol.h
index f6a207958459..ad21925af061 100644
--- a/net/mptcp/protocol.h
+++ b/net/mptcp/protocol.h
@@ -1199,6 +1199,8 @@ static inline void __mptcp_do_fallback(struct mptcp_sock *msk)
 		pr_debug("TCP fallback already done (msk=%p)\n", msk);
 		return;
 	}
+	if (WARN_ON_ONCE(!READ_ONCE(msk->allow_infinite_fallback)))
+		return;
 	set_bit(MPTCP_FALLBACK_DONE, &msk->flags);
 }
 
diff --git a/net/mptcp/subflow.c b/net/mptcp/subflow.c
index dfcbef9c4624..9f18217dddc8 100644
--- a/net/mptcp/subflow.c
+++ b/net/mptcp/subflow.c
@@ -1142,7 +1142,6 @@ static enum mapping_status get_mapping_status(struct sock *ssk,
 	if (data_len == 0) {
 		pr_debug("infinite mapping received\n");
 		MPTCP_INC_STATS(sock_net(ssk), MPTCP_MIB_INFINITEMAPRX);
-		subflow->map_data_len = 0;
 		return MAPPING_INVALID;
 	}
 
@@ -1286,18 +1285,6 @@ static void subflow_sched_work_if_closed(struct mptcp_sock *msk, struct sock *ss
 		mptcp_schedule_work(sk);
 }
 
-static bool subflow_can_fallback(struct mptcp_subflow_context *subflow)
-{
-	struct mptcp_sock *msk = mptcp_sk(subflow->conn);
-
-	if (subflow->mp_join)
-		return false;
-	else if (READ_ONCE(msk->csum_enabled))
-		return !subflow->valid_csum_seen;
-	else
-		return READ_ONCE(msk->allow_infinite_fallback);
-}
-
 static void mptcp_subflow_fail(struct mptcp_sock *msk, struct sock *ssk)
 {
 	struct mptcp_subflow_context *subflow = mptcp_subflow_ctx(ssk);
@@ -1393,7 +1380,7 @@ fallback:
 			return true;
 		}
 
-		if (!subflow_can_fallback(subflow) && subflow->map_data_len) {
+		if (!READ_ONCE(msk->allow_infinite_fallback)) {
 			/* fatal protocol error, close the socket.
 			 * subflow_error_report() will introduce the appropriate barriers
 			 */