mptcp: safety check before fallback

Recently, some fallback have been initiated, while the connection was
not supposed to fallback.

Add a safety check with a warning to detect when an wrong attempt to
fallback is being done. This should help detecting any future issues
quicker.

Acked-by: Paolo Abeni <pabeni@redhat.com>
Signed-off-by: Matthieu Baerts (NGI0) <matttbe@kernel.org>
Link: https://patch.msgid.link/20250224-net-mptcp-misc-fixes-v1-3-f550f636b435@kernel.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

diff --git a/net/mptcp/protocol.h b/net/mptcp/protocol.h
index f6a207958459db5bd39f91ed7431b5a766669f92..ad21925af061263d908bd9faddffaef979f46c93 100644 (file)
--- 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);
 }