From: Francesco Ruggeri fruggeri@arista.com
stable inclusion from linux-4.19.154 commit b221c4a1f8778923f1984092b132fe3e176677c4
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[ Upstream commit 4f25434bccc28cf8a07876ef5142a2869a674353 ]
If the first packet conntrack sees after a re-register is an outgoing keepalive packet with no data (SEG.SEQ = SND.NXT-1), td_end is set to SND.NXT-1. When the peer correctly acknowledges SND.NXT, tcp_in_window fails check III (Upper bound for valid (s)ack: sack <= receiver.td_end) and returns false, which cascades into nf_conntrack_in setting skb->_nfct = 0 and in later conntrack iptables rules not matching. In cases where iptables are dropping packets that do not match conntrack rules this can result in idle tcp connections to time out.
v2: adjust td_end when getting the reply rather than when sending out the keepalive packet.
Fixes: f94e63801ab2 ("netfilter: conntrack: reset tcp maxwin on re-register") Signed-off-by: Francesco Ruggeri fruggeri@arista.com Signed-off-by: Pablo Neira Ayuso pablo@netfilter.org Signed-off-by: Sasha Levin sashal@kernel.org Signed-off-by: Yang Yingliang yangyingliang@huawei.com --- net/netfilter/nf_conntrack_proto_tcp.c | 19 +++++++++++++------ 1 file changed, 13 insertions(+), 6 deletions(-)
diff --git a/net/netfilter/nf_conntrack_proto_tcp.c b/net/netfilter/nf_conntrack_proto_tcp.c index fe4b198bbbf0..ba14ef107f3c 100644 --- a/net/netfilter/nf_conntrack_proto_tcp.c +++ b/net/netfilter/nf_conntrack_proto_tcp.c @@ -544,13 +544,20 @@ static bool tcp_in_window(const struct nf_conn *ct, swin = win << sender->td_scale; sender->td_maxwin = (swin == 0 ? 1 : swin); sender->td_maxend = end + sender->td_maxwin; - /* - * We haven't seen traffic in the other direction yet - * but we have to tweak window tracking to pass III - * and IV until that happens. - */ - if (receiver->td_maxwin == 0) + if (receiver->td_maxwin == 0) { + /* We haven't seen traffic in the other + * direction yet but we have to tweak window + * tracking to pass III and IV until that + * happens. + */ receiver->td_end = receiver->td_maxend = sack; + } else if (sack == receiver->td_end + 1) { + /* Likely a reply to a keepalive. + * Needed for III. + */ + receiver->td_end++; + } + } } else if (((state->state == TCP_CONNTRACK_SYN_SENT && dir == IP_CT_DIR_ORIGINAL)