From 356d7d88e088687b6578ca64601b0a2c9d145296 Mon Sep 17 00:00:00 2001 From: Yuchung Cheng Date: Fri, 9 Aug 2013 17:21:27 -0700 Subject: [PATCH] netfilter: nf_conntrack: fix tcp_in_window for Fast Open Currently the conntrack checks if the ending sequence of a packet falls within the observed receive window. However it does so even if it has not observe any packet from the remote yet and uses an uninitialized receive window (td_maxwin). If a connection uses Fast Open to send a SYN-data packet which is dropped afterward in the network. The subsequent SYNs retransmits will all fail this check and be discarded, leading to a connection timeout. This is because the SYN retransmit does not contain data payload so end == initial sequence number (isn) + 1 sender->td_end == isn + syn_data_len receiver->td_maxwin == 0 The fix is to only apply this check after td_maxwin is initialized. Reported-by: Michael Chan Signed-off-by: Yuchung Cheng Acked-by: Eric Dumazet Acked-by: Jozsef Kadlecsik Signed-off-by: Pablo Neira Ayuso --- net/netfilter/nf_conntrack_proto_tcp.c | 12 ++++++++---- 1 file changed, 8 insertions(+), 4 deletions(-) diff --git a/net/netfilter/nf_conntrack_proto_tcp.c b/net/netfilter/nf_conntrack_proto_tcp.c index 7dcc376eea5f..2f8010707d01 100644 --- a/net/netfilter/nf_conntrack_proto_tcp.c +++ b/net/netfilter/nf_conntrack_proto_tcp.c @@ -526,7 +526,7 @@ static bool tcp_in_window(const struct nf_conn *ct, const struct nf_conntrack_tuple *tuple = &ct->tuplehash[dir].tuple; __u32 seq, ack, sack, end, win, swin; s16 receiver_offset; - bool res; + bool res, in_recv_win; /* * Get the required data from the packet. @@ -649,14 +649,18 @@ static bool tcp_in_window(const struct nf_conn *ct, receiver->td_end, receiver->td_maxend, receiver->td_maxwin, receiver->td_scale); + /* Is the ending sequence in the receive window (if available)? */ + in_recv_win = !receiver->td_maxwin || + after(end, sender->td_end - receiver->td_maxwin - 1); + pr_debug("tcp_in_window: I=%i II=%i III=%i IV=%i\n", before(seq, sender->td_maxend + 1), - after(end, sender->td_end - receiver->td_maxwin - 1), + (in_recv_win ? 1 : 0), before(sack, receiver->td_end + 1), after(sack, receiver->td_end - MAXACKWINDOW(sender) - 1)); if (before(seq, sender->td_maxend + 1) && - after(end, sender->td_end - receiver->td_maxwin - 1) && + in_recv_win && before(sack, receiver->td_end + 1) && after(sack, receiver->td_end - MAXACKWINDOW(sender) - 1)) { /* @@ -725,7 +729,7 @@ static bool tcp_in_window(const struct nf_conn *ct, nf_log_packet(net, pf, 0, skb, NULL, NULL, NULL, "nf_ct_tcp: %s ", before(seq, sender->td_maxend + 1) ? - after(end, sender->td_end - receiver->td_maxwin - 1) ? + in_recv_win ? before(sack, receiver->td_end + 1) ? after(sack, receiver->td_end - MAXACKWINDOW(sender) - 1) ? "BUG" : "ACK is under the lower bound (possible overly delayed ACK)"