linux-stable.git/net/netfilter, branch v3.2.67 Linux kernel stable tree netfilter: conntrack: disable generic tracking for known protocols 2015-02-20T00:49:42+00:00 Florian Westphal fw@strlen.de 2014-09-26T09:35:42+00:00 d7cde286daad20dd171247ea47fc5ff4868591f0 commit db29a9508a9246e77087c5531e45b2c88ec6988b upstream. Given following iptables ruleset: -P FORWARD DROP -A FORWARD -m sctp --dport 9 -j ACCEPT -A FORWARD -p tcp --dport 80 -j ACCEPT -A FORWARD -p tcp -m conntrack -m state ESTABLISHED,RELATED -j ACCEPT One would assume that this allows SCTP on port 9 and TCP on port 80. Unfortunately, if the SCTP conntrack module is not loaded, this allows *all* SCTP communication, to pass though, i.e. -p sctp -j ACCEPT, which we think is a security issue. This is because on the first SCTP packet on port 9, we create a dummy "generic l4" conntrack entry without any port information (since conntrack doesn't know how to extract this information). All subsequent packets that are unknown will then be in established state since they will fallback to proto_generic and will match the 'generic' entry. Our originally proposed version [1] completely disabled generic protocol tracking, but Jozsef suggests to not track protocols for which a more suitable helper is available, hence we now mitigate the issue for in tree known ct protocol helpers only, so that at least NAT and direction information will still be preserved for others. [1] http://www.spinics.net/lists/netfilter-devel/msg33430.html Joint work with Daniel Borkmann. Signed-off-by: Florian Westphal <fw@strlen.de> Signed-off-by: Daniel Borkmann <dborkman@redhat.com> Acked-by: Jozsef Kadlecsik <kadlec@blackhole.kfki.hu> Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org> [bwh: Backported to 3.2: adjust context] Signed-off-by: Ben Hutchings <ben@decadent.org.uk> 
commit db29a9508a9246e77087c5531e45b2c88ec6988b upstream.

Given following iptables ruleset:

-P FORWARD DROP
-A FORWARD -m sctp --dport 9 -j ACCEPT
-A FORWARD -p tcp --dport 80 -j ACCEPT
-A FORWARD -p tcp -m conntrack -m state ESTABLISHED,RELATED -j ACCEPT

One would assume that this allows SCTP on port 9 and TCP on port 80.
Unfortunately, if the SCTP conntrack module is not loaded, this allows
*all* SCTP communication, to pass though, i.e. -p sctp -j ACCEPT,
which we think is a security issue.

This is because on the first SCTP packet on port 9, we create a dummy
"generic l4" conntrack entry without any port information (since
conntrack doesn't know how to extract this information).

All subsequent packets that are unknown will then be in established
state since they will fallback to proto_generic and will match the
'generic' entry.

Our originally proposed version [1] completely disabled generic protocol
tracking, but Jozsef suggests to not track protocols for which a more
suitable helper is available, hence we now mitigate the issue for in
tree known ct protocol helpers only, so that at least NAT and direction
information will still be preserved for others.

 [1] http://www.spinics.net/lists/netfilter-devel/msg33430.html

Joint work with Daniel Borkmann.

Signed-off-by: Florian Westphal <fw@strlen.de>
Signed-off-by: Daniel Borkmann <dborkman@redhat.com>
Acked-by: Jozsef Kadlecsik <kadlec@blackhole.kfki.hu>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
[bwh: Backported to 3.2: adjust context]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
netfilter: ipset: small potential read beyond the end of buffer 2015-02-20T00:49:41+00:00 Dan Carpenter dan.carpenter@oracle.com 2014-11-10T16:11:21+00:00 d64fba0de2f9cc5519398e220c5537a5a881458f commit 2196937e12b1b4ba139806d132647e1651d655df upstream. We could be reading 8 bytes into a 4 byte buffer here. It seems harmless but adding a check is the right thing to do and it silences a static checker warning. Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com> Acked-by: Jozsef Kadlecsik <kadlec@blackhole.kfki.hu> Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org> Signed-off-by: Ben Hutchings <ben@decadent.org.uk> 
commit 2196937e12b1b4ba139806d132647e1651d655df upstream.

We could be reading 8 bytes into a 4 byte buffer here.  It seems
harmless but adding a check is the right thing to do and it silences a
static checker warning.

Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Acked-by: Jozsef Kadlecsik <kadlec@blackhole.kfki.hu>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
ipvs: avoid netns exit crash on ip_vs_conn_drop_conntrack 2014-11-05T20:27:49+00:00 Julian Anastasov ja@ssi.bg 2014-07-10T06:24:01+00:00 7756f3a8792b7696f3e7aed47671359af8bf549e commit 2627b7e15c5064ddd5e578e4efd948d48d531a3f upstream. commit 8f4e0a18682d91 ("IPVS netns exit causes crash in conntrack") added second ip_vs_conn_drop_conntrack call instead of just adding the needed check. As result, the first call still can cause crash on netns exit. Remove it. Signed-off-by: Julian Anastasov <ja@ssi.bg> Signed-off-by: Hans Schillstrom <hans@schillstrom.com> Signed-off-by: Simon Horman <horms@verge.net.au> Signed-off-by: Ben Hutchings <ben@decadent.org.uk> 
commit 2627b7e15c5064ddd5e578e4efd948d48d531a3f upstream.

commit 8f4e0a18682d91 ("IPVS netns exit causes crash in conntrack")
added second ip_vs_conn_drop_conntrack call instead of just adding
the needed check. As result, the first call still can cause
crash on netns exit. Remove it.

Signed-off-by: Julian Anastasov <ja@ssi.bg>
Signed-off-by: Hans Schillstrom <hans@schillstrom.com>
Signed-off-by: Simon Horman <horms@verge.net.au>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
inetpeer: get rid of ip_id_count 2014-09-13T22:41:48+00:00 Eric Dumazet edumazet@google.com 2014-06-02T12:26:03+00:00 64b5c251d5b2cee4a0f697bfb90d79263f6dd517 [ Upstream commit 73f156a6e8c1074ac6327e0abd1169e95eb66463 ] Ideally, we would need to generate IP ID using a per destination IP generator. linux kernels used inet_peer cache for this purpose, but this had a huge cost on servers disabling MTU discovery. 1) each inet_peer struct consumes 192 bytes 2) inetpeer cache uses a binary tree of inet_peer structs, with a nominal size of ~66000 elements under load. 3) lookups in this tree are hitting a lot of cache lines, as tree depth is about 20. 4) If server deals with many tcp flows, we have a high probability of not finding the inet_peer, allocating a fresh one, inserting it in the tree with same initial ip_id_count, (cf secure_ip_id()) 5) We garbage collect inet_peer aggressively. IP ID generation do not have to be 'perfect' Goal is trying to avoid duplicates in a short period of time, so that reassembly units have a chance to complete reassembly of fragments belonging to one message before receiving other fragments with a recycled ID. We simply use an array of generators, and a Jenkin hash using the dst IP as a key. ipv6_select_ident() is put back into net/ipv6/ip6_output.c where it belongs (it is only used from this file) secure_ip_id() and secure_ipv6_id() no longer are needed. Rename ip_select_ident_more() to ip_select_ident_segs() to avoid unnecessary decrement/increment of the number of segments. Signed-off-by: Eric Dumazet <edumazet@google.com> Signed-off-by: David S. Miller <davem@davemloft.net> Signed-off-by: Ben Hutchings <ben@decadent.org.uk> 
[ Upstream commit 73f156a6e8c1074ac6327e0abd1169e95eb66463 ]

Ideally, we would need to generate IP ID using a per destination IP
generator.

linux kernels used inet_peer cache for this purpose, but this had a huge
cost on servers disabling MTU discovery.

1) each inet_peer struct consumes 192 bytes

2) inetpeer cache uses a binary tree of inet_peer structs,
   with a nominal size of ~66000 elements under load.

3) lookups in this tree are hitting a lot of cache lines, as tree depth
   is about 20.

4) If server deals with many tcp flows, we have a high probability of
   not finding the inet_peer, allocating a fresh one, inserting it in
   the tree with same initial ip_id_count, (cf secure_ip_id())

5) We garbage collect inet_peer aggressively.

IP ID generation do not have to be 'perfect'

Goal is trying to avoid duplicates in a short period of time,
so that reassembly units have a chance to complete reassembly of
fragments belonging to one message before receiving other fragments
with a recycled ID.

We simply use an array of generators, and a Jenkin hash using the dst IP
as a key.

ipv6_select_ident() is put back into net/ipv6/ip6_output.c where it
belongs (it is only used from this file)

secure_ip_id() and secure_ipv6_id() no longer are needed.

Rename ip_select_ident_more() to ip_select_ident_segs() to avoid
unnecessary decrement/increment of the number of segments.

Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
ipvs: stop tot_stats estimator only under CONFIG_SYSCTL 2014-08-06T17:07:41+00:00 Julian Anastasov ja@ssi.bg 2014-07-16T08:26:47+00:00 25cc3a3e96212b82c5e079e115857da49a1ccc47 [ Upstream commit 9802d21e7a0b0d2167ef745edc1f4ea7a0fc6ea3 ] The tot_stats estimator is started only when CONFIG_SYSCTL is defined. But it is stopped without checking CONFIG_SYSCTL. Fix the crash by moving ip_vs_stop_estimator into ip_vs_control_net_cleanup_sysctl. The change is needed after commit 14e405461e664b ("IPVS: Add __ip_vs_control_{init,cleanup}_sysctl()") from 2.6.39. Reported-by: Jet Chen <jet.chen@intel.com> Tested-by: Jet Chen <jet.chen@intel.com> Signed-off-by: Julian Anastasov <ja@ssi.bg> Signed-off-by: Simon Horman <horms@verge.net.au> Signed-off-by: Ben Hutchings <ben@decadent.org.uk> 
[ Upstream commit 9802d21e7a0b0d2167ef745edc1f4ea7a0fc6ea3 ]

The tot_stats estimator is started only when CONFIG_SYSCTL
is defined. But it is stopped without checking CONFIG_SYSCTL.
Fix the crash by moving ip_vs_stop_estimator into
ip_vs_control_net_cleanup_sysctl.

The change is needed after commit 14e405461e664b
("IPVS: Add __ip_vs_control_{init,cleanup}_sysctl()") from 2.6.39.

Reported-by: Jet Chen <jet.chen@intel.com>
Tested-by: Jet Chen <jet.chen@intel.com>
Signed-off-by: Julian Anastasov <ja@ssi.bg>
Signed-off-by: Simon Horman <horms@verge.net.au>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
netfilter: nf_conntrack_dccp: fix skb_header_pointer API usages 2014-04-09T01:20:44+00:00 Daniel Borkmann dborkman@redhat.com 2014-01-05T23:57:54+00:00 5b866eaa34e4ddc312c927030fde5f6a6184ddc5 commit b22f5126a24b3b2f15448c3f2a254fc10cbc2b92 upstream. Some occurences in the netfilter tree use skb_header_pointer() in the following way ... struct dccp_hdr _dh, *dh; ... skb_header_pointer(skb, dataoff, sizeof(_dh), &dh); ... where dh itself is a pointer that is being passed as the copy buffer. Instead, we need to use &_dh as the forth argument so that we're copying the data into an actual buffer that sits on the stack. Currently, we probably could overwrite memory on the stack (e.g. with a possibly mal-formed DCCP packet), but unintentionally, as we only want the buffer to be placed into _dh variable. Fixes: 2bc780499aa3 ("[NETFILTER]: nf_conntrack: add DCCP protocol support") Signed-off-by: Daniel Borkmann <dborkman@redhat.com> Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org> Signed-off-by: Ben Hutchings <ben@decadent.org.uk> 
commit b22f5126a24b3b2f15448c3f2a254fc10cbc2b92 upstream.

Some occurences in the netfilter tree use skb_header_pointer() in
the following way ...

  struct dccp_hdr _dh, *dh;
  ...
  skb_header_pointer(skb, dataoff, sizeof(_dh), &dh);

... where dh itself is a pointer that is being passed as the copy
buffer. Instead, we need to use &_dh as the forth argument so that
we're copying the data into an actual buffer that sits on the stack.

Currently, we probably could overwrite memory on the stack (e.g.
with a possibly mal-formed DCCP packet), but unintentionally, as
we only want the buffer to be placed into _dh variable.

Fixes: 2bc780499aa3 ("[NETFILTER]: nf_conntrack: add DCCP protocol support")
Signed-off-by: Daniel Borkmann <dborkman@redhat.com>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
netfilter: nf_ct_sip: don't drop packets with offsets pointing outside the packet 2013-11-28T14:02:00+00:00 Patrick McHardy kaber@trash.net 2013-04-05T08:13:30+00:00 bb116a889998b2385f57b4295c957c11395be049 commit 3a7b21eaf4fb3c971bdb47a98f570550ddfe4471 upstream. Some Cisco phones create huge messages that are spread over multiple packets. After calculating the offset of the SIP body, it is validated to be within the packet and the packet is dropped otherwise. This breaks operation of these phones. Since connection tracking is supposed to be passive, just let those packets pass unmodified and untracked. Signed-off-by: Patrick McHardy <kaber@trash.net> Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org> [bwh: Backported to 3.2: there is no log message to delete] Signed-off-by: Ben Hutchings <ben@decadent.org.uk> 
commit 3a7b21eaf4fb3c971bdb47a98f570550ddfe4471 upstream.

Some Cisco phones create huge messages that are spread over multiple packets.
After calculating the offset of the SIP body, it is validated to be within
the packet and the packet is dropped otherwise. This breaks operation of
these phones. Since connection tracking is supposed to be passive, just let
those packets pass unmodified and untracked.

Signed-off-by: Patrick McHardy <kaber@trash.net>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
[bwh: Backported to 3.2: there is no log message to delete]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
ip: generate unique IP identificator if local fragmentation is allowed 2013-10-26T20:06:08+00:00 Ansis Atteka aatteka@nicira.com 2013-09-18T22:29:53+00:00 dee5590a22d03d7e974ef6956747d717ef5de061 [ Upstream commit 703133de331a7a7df47f31fb9de51dc6f68a9de8 ] If local fragmentation is allowed, then ip_select_ident() and ip_select_ident_more() need to generate unique IDs to ensure correct defragmentation on the peer. For example, if IPsec (tunnel mode) has to encrypt large skbs that have local_df bit set, then all IP fragments that belonged to different ESP datagrams would have used the same identificator. If one of these IP fragments would get lost or reordered, then peer could possibly stitch together wrong IP fragments that did not belong to the same datagram. This would lead to a packet loss or data corruption. Signed-off-by: Ansis Atteka <aatteka@nicira.com> Signed-off-by: David S. Miller <davem@davemloft.net> Signed-off-by: Ben Hutchings <ben@decadent.org.uk> 
[ Upstream commit 703133de331a7a7df47f31fb9de51dc6f68a9de8 ]

If local fragmentation is allowed, then ip_select_ident() and
ip_select_ident_more() need to generate unique IDs to ensure
correct defragmentation on the peer.

For example, if IPsec (tunnel mode) has to encrypt large skbs
that have local_df bit set, then all IP fragments that belonged
to different ESP datagrams would have used the same identificator.
If one of these IP fragments would get lost or reordered, then
peer could possibly stitch together wrong IP fragments that did
not belong to the same datagram. This would lead to a packet loss
or data corruption.

Signed-off-by: Ansis Atteka <aatteka@nicira.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
ipvs: ip_vs_sip_fill_param() BUG: bad check of return value 2013-05-30T13:35:09+00:00 Hans Schillstrom hans@schillstrom.com 2013-04-27T18:06:14+00:00 3bda05cf930f4d93cea39f157a069472db1be266 commit f7a1dd6e3ad59f0cfd51da29dfdbfd54122c5916 upstream. The reason for this patch is crash in kmemdup caused by returning from get_callid with uniialized matchoff and matchlen. Removing Zero check of matchlen since it's done by ct_sip_get_header() BUG: unable to handle kernel paging request at ffff880457b5763f IP: [<ffffffff810df7fc>] kmemdup+0x2e/0x35 PGD 27f6067 PUD 0 Oops: 0000 [#1] PREEMPT SMP Modules linked in: xt_state xt_helper nf_conntrack_ipv6 nf_defrag_ipv6 ip6table_mangle xt_connmark xt_conntrack ip6_tables nf_conntrack_ftp ip_vs_ftp nf_nat xt_tcpudp iptable_mangle xt_mark ip_tables x_tables ip_vs_rr ip_vs_lblcr ip_vs_pe_sip ip_vs nf_conntrack_sip nf_conntrack bonding igb i2c_algo_bit i2c_core CPU 5 Pid: 0, comm: swapper/5 Not tainted 3.9.0-rc5+ #5 /S1200KP RIP: 0010:[<ffffffff810df7fc>] [<ffffffff810df7fc>] kmemdup+0x2e/0x35 RSP: 0018:ffff8803fea03648 EFLAGS: 00010282 RAX: ffff8803d61063e0 RBX: 0000000000000003 RCX: 0000000000000003 RDX: 0000000000000003 RSI: ffff880457b5763f RDI: ffff8803d61063e0 RBP: ffff8803fea03658 R08: 0000000000000008 R09: 0000000000000011 R10: 0000000000000011 R11: 00ffffffff81a8a3 R12: ffff880457b5763f R13: ffff8803d67f786a R14: ffff8803fea03730 R15: ffffffffa0098e90 FS: 0000000000000000(0000) GS:ffff8803fea00000(0000) knlGS:0000000000000000 CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 CR2: ffff880457b5763f CR3: 0000000001a0c000 CR4: 00000000001407e0 DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000 DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000400 Process swapper/5 (pid: 0, threadinfo ffff8803ee18c000, task ffff8803ee18a480) Stack: ffff8803d822a080 000000000000001c ffff8803fea036c8 ffffffffa000937a ffffffff81f0d8a0 000000038135fdd5 ffff880300000014 ffff880300110000 ffffffff150118ac ffff8803d7e8a000 ffff88031e0118ac 0000000000000000 Call Trace: <IRQ> [<ffffffffa000937a>] ip_vs_sip_fill_param+0x13a/0x187 [ip_vs_pe_sip] [<ffffffffa007b209>] ip_vs_sched_persist+0x2c6/0x9c3 [ip_vs] [<ffffffff8107dc53>] ? __lock_acquire+0x677/0x1697 [<ffffffff8100972e>] ? native_sched_clock+0x3c/0x7d [<ffffffff8100972e>] ? native_sched_clock+0x3c/0x7d [<ffffffff810649bc>] ? sched_clock_cpu+0x43/0xcf [<ffffffffa007bb1e>] ip_vs_schedule+0x181/0x4ba [ip_vs] ... Signed-off-by: Hans Schillstrom <hans@schillstrom.com> Acked-by: Julian Anastasov <ja@ssi.bg> Signed-off-by: Simon Horman <horms@verge.net.au> Signed-off-by: David S. Miller <davem@davemloft.net> Signed-off-by: Ben Hutchings <ben@decadent.org.uk> 
commit f7a1dd6e3ad59f0cfd51da29dfdbfd54122c5916 upstream.

The reason for this patch is crash in kmemdup
caused by returning from get_callid with uniialized
matchoff and matchlen.

Removing Zero check of matchlen since it's done by ct_sip_get_header()

BUG: unable to handle kernel paging request at ffff880457b5763f
IP: [<ffffffff810df7fc>] kmemdup+0x2e/0x35
PGD 27f6067 PUD 0
Oops: 0000 [#1] PREEMPT SMP
Modules linked in: xt_state xt_helper nf_conntrack_ipv6 nf_defrag_ipv6 ip6table_mangle xt_connmark xt_conntrack ip6_tables nf_conntrack_ftp ip_vs_ftp nf_nat xt_tcpudp iptable_mangle xt_mark ip_tables x_tables ip_vs_rr ip_vs_lblcr ip_vs_pe_sip ip_vs nf_conntrack_sip nf_conntrack bonding igb i2c_algo_bit i2c_core
CPU 5
Pid: 0, comm: swapper/5 Not tainted 3.9.0-rc5+ #5                  /S1200KP
RIP: 0010:[<ffffffff810df7fc>]  [<ffffffff810df7fc>] kmemdup+0x2e/0x35
RSP: 0018:ffff8803fea03648  EFLAGS: 00010282
RAX: ffff8803d61063e0 RBX: 0000000000000003 RCX: 0000000000000003
RDX: 0000000000000003 RSI: ffff880457b5763f RDI: ffff8803d61063e0
RBP: ffff8803fea03658 R08: 0000000000000008 R09: 0000000000000011
R10: 0000000000000011 R11: 00ffffffff81a8a3 R12: ffff880457b5763f
R13: ffff8803d67f786a R14: ffff8803fea03730 R15: ffffffffa0098e90
FS:  0000000000000000(0000) GS:ffff8803fea00000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: ffff880457b5763f CR3: 0000000001a0c000 CR4: 00000000001407e0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000400
Process swapper/5 (pid: 0, threadinfo ffff8803ee18c000, task ffff8803ee18a480)
Stack:
 ffff8803d822a080 000000000000001c ffff8803fea036c8 ffffffffa000937a
 ffffffff81f0d8a0 000000038135fdd5 ffff880300000014 ffff880300110000
 ffffffff150118ac ffff8803d7e8a000 ffff88031e0118ac 0000000000000000
Call Trace:
 <IRQ>

 [<ffffffffa000937a>] ip_vs_sip_fill_param+0x13a/0x187 [ip_vs_pe_sip]
 [<ffffffffa007b209>] ip_vs_sched_persist+0x2c6/0x9c3 [ip_vs]
 [<ffffffff8107dc53>] ? __lock_acquire+0x677/0x1697
 [<ffffffff8100972e>] ? native_sched_clock+0x3c/0x7d
 [<ffffffff8100972e>] ? native_sched_clock+0x3c/0x7d
 [<ffffffff810649bc>] ? sched_clock_cpu+0x43/0xcf
 [<ffffffffa007bb1e>] ip_vs_schedule+0x181/0x4ba [ip_vs]
...

Signed-off-by: Hans Schillstrom <hans@schillstrom.com>
Acked-by: Julian Anastasov <ja@ssi.bg>
Signed-off-by: Simon Horman <horms@verge.net.au>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
netfilter: Validate the sequence number of dataless ACK packets as well 2012-12-06T11:20:10+00:00 Jozsef Kadlecsik kadlec@blackhole.kfki.hu 2012-08-31T09:55:54+00:00 58fd4b237523afd2a925ccc664d35f0334da4ffd commit 4a70bbfaef0361d27272629d1a250a937edcafe4 upstream. We spare nothing by not validating the sequence number of dataless ACK packets and enabling it makes harder off-path attacks. See: "Reflection scan: an Off-Path Attack on TCP" by Jan Wrobel, http://arxiv.org/abs/1201.2074 Signed-off-by: Jozsef Kadlecsik <kadlec@blackhole.kfki.hu> Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org> Signed-off-by: Ben Hutchings <ben@decadent.org.uk> 
commit 4a70bbfaef0361d27272629d1a250a937edcafe4 upstream.

We spare nothing by not validating the sequence number of dataless
ACK packets and enabling it makes harder off-path attacks.

See: "Reflection scan: an Off-Path Attack on TCP" by Jan Wrobel,
http://arxiv.org/abs/1201.2074

Signed-off-by: Jozsef Kadlecsik <kadlec@blackhole.kfki.hu>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>