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Subject[PATCH 4.15 35/72] netfilter: drop template ct when conntrack is skipped.
4.15-stable review patch.  If anyone has any objections, please let me know.


From: Paolo Abeni <>

commit aebfa52a925d701114afd6af0def35bab16d4f47 upstream.

The ipv4 nf_ct code currently skips the nf_conntrak_in() call
for fragmented packets. As a results later matches/target can end
up manipulating template ct entry instead of 'real' ones.

Exploiting the above, syzbot found a way to trigger the following

WARNING: CPU: 1 PID: 4242 at net/netfilter/xt_cluster.c:55
xt_cluster_mt+0x6c1/0x840 net/netfilter/xt_cluster.c:127
Kernel panic - not syncing: panic_on_warn set ...

CPU: 1 PID: 4242 Comm: syzkaller027971 Not tainted 4.16.0-rc2+ #243
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS
Google 01/01/2011
Call Trace:
__dump_stack lib/dump_stack.c:17 [inline]
dump_stack+0x194/0x24d lib/dump_stack.c:53
panic+0x1e4/0x41c kernel/panic.c:183
__warn+0x1dc/0x200 kernel/panic.c:547
report_bug+0x211/0x2d0 lib/bug.c:184
fixup_bug.part.11+0x37/0x80 arch/x86/kernel/traps.c:178
fixup_bug arch/x86/kernel/traps.c:247 [inline]
do_error_trap+0x2d7/0x3e0 arch/x86/kernel/traps.c:296
do_invalid_op+0x1b/0x20 arch/x86/kernel/traps.c:315
invalid_op+0x58/0x80 arch/x86/entry/entry_64.S:957
RIP: 0010:xt_cluster_hash net/netfilter/xt_cluster.c:55 [inline]
RIP: 0010:xt_cluster_mt+0x6c1/0x840 net/netfilter/xt_cluster.c:127
RSP: 0018:ffff8801d2f6f2d0 EFLAGS: 00010293
RAX: ffff8801af700540 RBX: 0000000000000000 RCX: ffffffff84a2d1e1
RDX: 0000000000000000 RSI: ffff8801d2f6f478 RDI: ffff8801cafd336a
RBP: ffff8801d2f6f2e8 R08: 0000000000000000 R09: 0000000000000001
R10: 0000000000000000 R11: 0000000000000000 R12: ffff8801b03b3d18
R13: ffff8801cafd3300 R14: dffffc0000000000 R15: ffff8801d2f6f478
ipt_do_table+0xa91/0x19b0 net/ipv4/netfilter/ip_tables.c:296
iptable_filter_hook+0x65/0x80 net/ipv4/netfilter/iptable_filter.c:41
nf_hook_entry_hookfn include/linux/netfilter.h:120 [inline]
nf_hook_slow+0xba/0x1a0 net/netfilter/core.c:483
nf_hook include/linux/netfilter.h:243 [inline]
NF_HOOK include/linux/netfilter.h:286 [inline]
raw_send_hdrinc.isra.17+0xf39/0x1880 net/ipv4/raw.c:432
raw_sendmsg+0x14cd/0x26b0 net/ipv4/raw.c:669
inet_sendmsg+0x11f/0x5e0 net/ipv4/af_inet.c:763
sock_sendmsg_nosec net/socket.c:629 [inline]
sock_sendmsg+0xca/0x110 net/socket.c:639
SYSC_sendto+0x361/0x5c0 net/socket.c:1748
SyS_sendto+0x40/0x50 net/socket.c:1716
do_syscall_64+0x280/0x940 arch/x86/entry/common.c:287
RIP: 0033:0x441b49
RSP: 002b:00007ffff5ca8b18 EFLAGS: 00000216 ORIG_RAX: 000000000000002c
RAX: ffffffffffffffda RBX: 00000000004002c8 RCX: 0000000000441b49
RDX: 0000000000000030 RSI: 0000000020ff7000 RDI: 0000000000000003
RBP: 00000000006cc018 R08: 000000002066354c R09: 0000000000000010
R10: 0000000000000000 R11: 0000000000000216 R12: 0000000000403470
R13: 0000000000403500 R14: 0000000000000000 R15: 0000000000000000
Dumping ftrace buffer:
(ftrace buffer empty)
Kernel Offset: disabled
Rebooting in 86400 seconds..

Instead of adding checks for template ct on every target/match
manipulating skb->_nfct, simply drop the template ct when skipping

Fixes: 7b4fdf77a450ec ("netfilter: don't track fragmented packets")
Signed-off-by: Paolo Abeni <>
Acked-by: Florian Westphal <>
Signed-off-by: Pablo Neira Ayuso <>
Signed-off-by: Greg Kroah-Hartman <>

net/ipv4/netfilter/nf_conntrack_l3proto_ipv4.c | 14 +++++++++++++-
1 file changed, 13 insertions(+), 1 deletion(-)

--- a/net/ipv4/netfilter/nf_conntrack_l3proto_ipv4.c
+++ b/net/ipv4/netfilter/nf_conntrack_l3proto_ipv4.c
@@ -159,8 +159,20 @@ static unsigned int ipv4_conntrack_local
ip_hdrlen(skb) < sizeof(struct iphdr))
return NF_ACCEPT;

- if (ip_is_fragment(ip_hdr(skb))) /* IP_NODEFRAG setsockopt set */
+ if (ip_is_fragment(ip_hdr(skb))) { /* IP_NODEFRAG setsockopt set */
+ enum ip_conntrack_info ctinfo;
+ struct nf_conn *tmpl;
+ tmpl = nf_ct_get(skb, &ctinfo);
+ if (tmpl && nf_ct_is_template(tmpl)) {
+ /* when skipping ct, clear templates to avoid fooling
+ * later targets/matches
+ */
+ skb->_nfct = 0;
+ nf_ct_put(tmpl);
+ }
return NF_ACCEPT;
+ }

return nf_conntrack_in(state->net, PF_INET, state->hook, skb);

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