Since commit 41d73ec0 (netfilter: nf_conntrack: make sequence
number adjustments usuable without NAT), the sequence number extension
is dynamically allocated.

Instead of dying, give a WARN splash, in case of wrong usage of the
seqadj code, e.g. when forgetting to allocate via nfct_seqadj_ext_add().

Wrong usage have been seen in the IPVS code path.
Signed-off-by: NJesper Dangaard Brouer <brouer@redhat.com>
Acked-by: NJulian Anastasov <ja@ssi.bg>
Signed-off-by: NSimon Horman <horms@verge.net.au>

In commit 41d73ec0, sequence number adjustments were moved to a
separate file. Unfortunately, the sequence numbers that are stored
in the nf_ct_seqadj structure are expressed in host byte order. The
necessary ntohl call was removed when the call to adjust_tcp_sequence
was collapsed into nf_ct_seqadj_set. This broke the FTP NAT helper.
Fix it by adding back the byte order conversions.
Reported-by: NDawid Stawiarski <dawid.stawiarski@netart.pl>
Signed-off-by: NPhil Oester <kernel@linuxace.com>
Signed-off-by: NPablo Neira Ayuso <pablo@netfilter.org>

Add a SYNPROXY for netfilter. The code is split into two parts, the synproxy
core with common functions and an address family specific target.

The SYNPROXY receives the connection request from the client, responds with
a SYN/ACK containing a SYN cookie and announcing a zero window and checks
whether the final ACK from the client contains a valid cookie.

It then establishes a connection to the original destination and, if
successful, sends a window update to the client with the window size
announced by the server.

Support for timestamps, SACK, window scaling and MSS options can be
statically configured as target parameters if the features of the server
are known. If timestamps are used, the timestamp value sent back to
the client in the SYN/ACK will be different from the real timestamp of
the server. In order to now break PAWS, the timestamps are translated in
the direction server->client.
Signed-off-by: NPatrick McHardy <kaber@trash.net>
Tested-by: NMartin Topholm <mph@one.com>
Signed-off-by: NJesper Dangaard Brouer <brouer@redhat.com>
Signed-off-by: NPablo Neira Ayuso <pablo@netfilter.org>

Split out sequence number adjustments from NAT and move them to the conntrack
core to make them usable for SYN proxying. The sequence number adjustment
information is moved to a seperate extend. The extend is added to new
conntracks when a NAT mapping is set up for a connection using a helper.

As a side effect, this saves 24 bytes per connection with NAT in the common
case that a connection does not have a helper assigned.
Signed-off-by: NPatrick McHardy <kaber@trash.net>
Tested-by: NMartin Topholm <mph@one.com>
Signed-off-by: NJesper Dangaard Brouer <brouer@redhat.com>
Signed-off-by: NPablo Neira Ayuso <pablo@netfilter.org>