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netfilter: nf_conntrack_tcp: fixing to check the lower bound of valid ACK

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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>
This commit is contained in:
Jozsef Kadlecsik 2008-06-30 12:41:30 -07:00 committed by David S. Miller
parent d420895efb
commit 84ebe1cdae
1 changed files with 7 additions and 6 deletions
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13
net/netfilter/nf_conntrack_proto_tcp.c
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@ -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).
*/