netdev - Re: [PATCH nf] netfilter: drop template ct when conntrack is skipped.

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Date:   Thu, 22 Mar 2018 12:56:28 +0100
From:   Pablo Neira Ayuso <pablo@...filter.org>
To:     Paolo Abeni <pabeni@...hat.com>
Cc:     netdev@...r.kernel.org, Florian Westphal <fw@...len.de>,
        netfilter-devel@...r.kernel.org, coreteam@...filter.org,
        syzbot+0346441ae0545cfcea3a@...kaller.appspotmail.com,
        syzkaller-bugs@...glegroups.com
Subject: Re: [PATCH nf] netfilter: drop template ct when conntrack is skipped.

On Thu, Mar 22, 2018 at 11:08:50AM +0100, Paolo Abeni wrote:
> 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
> splat:
> 
> 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
>   entry_SYSCALL_64_after_hwframe+0x42/0xb7
> 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
> nf_conntrack_in().

Applied, thanks.