The nipa CI is reporting frequent failures in the mptcp_connect self-tests. In the failing scenarios (TCP -> MPTCP) the involved sockets are actually plain TCP ones, as fallback for passive socket at 2whs time cause the MPTCP listener to actually create a TCP socket. The transfer is stuck due to the receiver buffer being zero. With the stronger check in place, tcp_clamp_window() can be invoked while the TCP socket has sk_rmem_alloc == 0, and the receive buffer will be zeroed, too. Check for the critical condition in tcp_prune_queue() and just drop the packet without shrinking the receiver buffer. Fixes: 1d2fbaad7cd8 ("tcp: stronger sk_rcvbuf checks") Suggested-by: Eric Dumazet Signed-off-by: Paolo Abeni --- v1 -> v2: - do not account for truesize, check for 0 rmem instead --- net/ipv4/tcp_input.c | 4 ++++ 1 file changed, 4 insertions(+) diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c index 672cbfbdcec1..81b6d3770812 100644 --- a/net/ipv4/tcp_input.c +++ b/net/ipv4/tcp_input.c @@ -5549,6 +5549,10 @@ static int tcp_prune_queue(struct sock *sk, const struct sk_buff *in_skb) { struct tcp_sock *tp = tcp_sk(sk); + /* Do nothing if our queues are empty. */ + if (!atomic_read(&sk->sk_rmem_alloc)) + return -1; + NET_INC_STATS(sock_net(sk), LINUX_MIB_PRUNECALLED); if (!tcp_can_ingest(sk, in_skb)) -- 2.50.0 The mentioned MIB is currently incremented even when a packet with an old sequence number (i.e. a zero window probe) is received, which is IMHO misleading. Explicitly restrict such MIB increment at the relevant events. Fixes: 6c758062c64d ("tcp: add LINUX_MIB_BEYOND_WINDOW") Acked-by: Eric Dumazet Signed-off-by: Paolo Abeni --- net/ipv4/tcp_input.c | 6 +++++- 1 file changed, 5 insertions(+), 1 deletion(-) diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c index 81b6d3770812..71b76e98371a 100644 --- a/net/ipv4/tcp_input.c +++ b/net/ipv4/tcp_input.c @@ -5915,7 +5915,11 @@ static bool tcp_validate_incoming(struct sock *sk, struct sk_buff *skb, if (!th->rst) { if (th->syn) goto syn_challenge; - NET_INC_STATS(sock_net(sk), LINUX_MIB_BEYOND_WINDOW); + + if (reason == SKB_DROP_REASON_TCP_INVALID_SEQUENCE || + reason == SKB_DROP_REASON_TCP_INVALID_END_SEQUENCE) + NET_INC_STATS(sock_net(sk), + LINUX_MIB_BEYOND_WINDOW); if (!tcp_oow_rate_limited(sock_net(sk), skb, LINUX_MIB_TCPACKSKIPPEDSEQ, &tp->last_oow_ack_time)) -- 2.50.0