From 84ebe1cdae56707b9aa1b40ae5aa7d817ba745f5 Mon Sep 17 00:00:00 2001 From: Jozsef Kadlecsik Date: Mon, 30 Jun 2008 12:41:30 -0700 Subject: [PATCH] netfilter: nf_conntrack_tcp: fixing to check the lower bound of valid ACK MIME-Version: 1.0 Content-Type: text/plain; charset=utf8 Content-Transfer-Encoding: 8bit Lost connections was reported by Thomas Bätzler (running 2.6.25 kernel) on the netfilter mailing list (see the thread "Weird nat/conntrack Problem with PASV FTP upload"). He provided tcpdump recordings which helped to find a long lingering bug in conntrack. In TCP connection tracking, checking the lower bound of valid ACK could lead to mark valid packets as INVALID because: - We have got a "higher or equal" inequality, but the test checked the "higher" condition only; fixed. - If the packet contains a SACK option, it could occur that the ACK value was before the left edge of our (S)ACK "window": if a previous packet from the other party intersected the right edge of the window of the receiver, we could move forward the window parameters beyond accepting a valid ack. Therefore in this patch we check the rightmost SACK edge instead of the ACK value in the lower bound of valid (S)ACK test. Signed-off-by: Jozsef Kadlecsik Signed-off-by: Patrick McHardy Signed-off-by: David S. Miller --- net/netfilter/nf_conntrack_proto_tcp.c | 13 +++++++------ 1 file changed, 7 insertions(+), 6 deletions(-) diff --git a/net/netfilter/nf_conntrack_proto_tcp.c b/net/netfilter/nf_conntrack_proto_tcp.c index ba94004fe3..271cd01d57 100644 --- a/net/netfilter/nf_conntrack_proto_tcp.c +++ b/net/netfilter/nf_conntrack_proto_tcp.c @@ -331,12 +331,13 @@ static unsigned int get_conntrack_index(const struct tcphdr *tcph) I. Upper bound for valid data: seq <= sender.td_maxend II. Lower bound for valid data: seq + len >= sender.td_end - receiver.td_maxwin - III. Upper bound for valid ack: sack <= receiver.td_end - IV. Lower bound for valid ack: ack >= receiver.td_end - MAXACKWINDOW + III. Upper bound for valid (s)ack: sack <= receiver.td_end + IV. Lower bound for valid (s)ack: sack >= receiver.td_end - MAXACKWINDOW - where sack is the highest right edge of sack block found in the packet. + where sack is the highest right edge of sack block found in the packet + or ack in the case of packet without SACK option. - The upper bound limit for a valid ack is not ignored - + The upper bound limit for a valid (s)ack is not ignored - we doesn't have to deal with fragments. */ @@ -606,12 +607,12 @@ static bool tcp_in_window(const struct nf_conn *ct, before(seq, sender->td_maxend + 1), after(end, sender->td_end - receiver->td_maxwin - 1), before(sack, receiver->td_end + 1), - after(ack, receiver->td_end - MAXACKWINDOW(sender))); + after(sack, receiver->td_end - MAXACKWINDOW(sender) - 1)); if (before(seq, sender->td_maxend + 1) && after(end, sender->td_end - receiver->td_maxwin - 1) && before(sack, receiver->td_end + 1) && - after(ack, receiver->td_end - MAXACKWINDOW(sender))) { + after(sack, receiver->td_end - MAXACKWINDOW(sender) - 1)) { /* * Take into account window scaling (RFC 1323). */ -- 2.39.5