From: Christoph Paasch <cpaasch@xxxxxxxxxx>
When skb_ext_add(skb, SKB_EXT_MPTCP) fails in mptcp_incoming_options(),
we used to return true, letting the segment proceed through the TCP
receive path without a DSS mapping. Such segments can leave inconsistent
mapping state and trigger a mid-stream fallback to TCP, which in testing
collapsed (by artificially forcing failures in skb_ext_add) throughput
to zero.
Return false instead so the TCP input path drops the skb (see
tcp_data_queue() and step-7 processing). This is the safer choice
under memory pressure: it preserves MPTCP correctness and provides
backpressure to the sender.
Control packets remain unaffected: ACK updates and DATA_FIN handling
happen before attempting the extension allocation, and tcp_reset()
continues to ignore the return value.
With this change, MPTCP continues to work at high throughput if we
artificially inject failures into skb_ext_add.
Fixes: 6787b7e350d3 ("mptcp: avoid processing packet if a subflow reset")
Cc: stable@xxxxxxxxxxxxxxx
Signed-off-by: Christoph Paasch <cpaasch@xxxxxxxxxx>
Reviewed-by: Matthieu Baerts (NGI0) <matttbe@xxxxxxxxxx>
Signed-off-by: Matthieu Baerts (NGI0) <matttbe@xxxxxxxxxx>
---
net/mptcp/options.c | 6 ++++--
1 file changed, 4 insertions(+), 2 deletions(-)
diff --git a/net/mptcp/options.c b/net/mptcp/options.c
index 70c0ab0ecf905d282e5dc6c1b21ffc6476c8d71b..2a8ea28442b271675411d190604073f779bee7fa 100644
--- a/net/mptcp/options.c
+++ b/net/mptcp/options.c
@@ -1118,7 +1118,9 @@ static bool add_addr_hmac_valid(struct mptcp_sock *msk,
return hmac == mp_opt->ahmac;
}
-/* Return false if a subflow has been reset, else return true */
+/* Return false in case of error (or subflow has been reset),
+ * else return true.
+ */
bool mptcp_incoming_options(struct sock *sk, struct sk_buff *skb)
{
struct mptcp_subflow_context *subflow = mptcp_subflow_ctx(sk);
@@ -1222,7 +1224,7 @@ bool mptcp_incoming_options(struct sock *sk, struct sk_buff *skb)
mpext = skb_ext_add(skb, SKB_EXT_MPTCP);
if (!mpext)
- return true;
+ return false;
memset(mpext, 0, sizeof(*mpext));
--
2.50.0
