netfilter: nf_conntrack_tcp: fixing to check the lower bound of valid ACK
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 <kadlec@blackhole.kfki.hu>
Signed-off-by: Patrick McHardy <kaber@trash.net>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/netfilter/nf_conntrack_proto_tcp.c b/net/netfilter/nf_conntrack_proto_tcp.c
index ba94004..271cd01 100644
--- a/net/netfilter/nf_conntrack_proto_tcp.c
+++ b/net/netfilter/nf_conntrack_proto_tcp.c
@@ -331,12 +331,13 @@
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 @@
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).
*/
