Date:   Tue, 17 Jul 2018 16:13:58 +0200
From:   Dmitry Vyukov <dvyukov@...gle.com>
To:     Florian Westphal <fw@...len.de>
Cc:     Eric Dumazet <eric.dumazet@...il.com>,
        Eric Dumazet <edumazet@...gle.com>,
        Pablo Neira Ayuso <pablo@...filter.org>,
        Jozsef Kadlecsik <kadlec@...ckhole.kfki.hu>,
        netfilter-devel@...r.kernel.org, netdev <netdev@...r.kernel.org>
Subject: Re: [PATCH net] netfilter: nf_conntrack: prevent uninit-value in gc_worker

On Tue, Jul 17, 2018 at 3:59 PM, Florian Westphal <fw@...len.de> wrote:
> Dmitry Vyukov <dvyukov@...gle.com> wrote:
>> What should have been initialized it?
>
> nf_ct_refresh_acct()
>
>> I assume it should have been happened in between init_conntrack and
>> nf_conntrack_confirm, because nf_conntrack_confirm already adds to an
>> uninit timeout value.
>
> Yes.
>
>> Since we got only 3 such reports and no reproducer, I would suspect
>> that there is some race involved. Is it possible that timeout
>> initialization (presumably a call to nf_ct_refresh_acct) happens after
>> and non-atomically with the corresponding connection state update, so
>> that the call to nf_conntrack_confirm sneaks before it?
>
> Unconfirmed conntrack isn't in the hash table, so all events should
> occur in order on same cpu:
> 1. allocation (init_conntrack)
> 2. timeout initialisation (via l4 tracker, can be generic one too)
> 3. nf_conntrack_confirm (insertion in hash table)
>
> What could be possible is that another core is registering/unregistering
> the conntrack hooks in parallel, I guess in that case we could have:
>
> 1. allocation (init_conntrack)
> (other cpu: remove conntrack hooks)
> (other cpu: add conntrack hooks)
> 3. nf_conntrack_confirm (insertion in hash table)
>
> Just a theory of course.
> In any case patch looks good to me.



We also got 30 of the following reports, which look quite similar.
That bug also have 2 reproducers, but they look more or less as just
sending a packet:

# See https://goo.gl/kgGztJ for information about syzkaller reproducers.
#{"threaded":true,"repeat":true,"procs":8,"sandbox":"","fault_call":-1}
r0 = socket$inet6(0xa, 0x3, 0x20000000021)
sendto$inet6(r0, &(0x7f0000000000), 0xfedf, 0x0,
&(0x7f0000000180)={0xa, 0x0, 0x0, @local={0xfe, 0x80, [], 0xaa}},
0x1a)
openat$snapshot(0xffffffffffffff9c,
&(0x7f0000000000)='/dev/snapshot\x00', 0xa0000, 0x0)


# See https://goo.gl/kgGztJ for information about syzkaller reproducers.
#{"repeat":true,"procs":1,"sandbox":"none","fault_call":-1,"netdev":true}
r0 = socket$inet6(0xa, 0x3, 0x3c)
connect$inet6(r0, &(0x7f0000000180)={0xa, 0x0, 0x0, @remote={0xfe,
0x80, [], 0xbb}, 0x9}, 0x1c)
sendto$inet6(r0, &(0x7f0000000200)='!', 0x1, 0x8000, 0x0, 0x0)
sendmsg(r0, &(0x7f0000000040)={0x0, 0x0,
&(0x7f0000000080)=[{&(0x7f0000000300)="119a0e63c9476288b671afdbd53a5994e137381f62021d1951b627b8dda57a5d17d744648c81c5703ed8146ab1b0171f89091b1dd323ff07dbb633fb3804849f7768e586df460963245dedb4013ee555af99499e44ad420dbf65fd46fbc9ba1274429e2d5783751815828ec8cb3553110cca66460215353d19f6d8bbd8fb08ad0491634ac2fd10e2cd30bcd7fede24263a7fff16e53ea293f3551b7147c33a44ea437fb1f77f94db4e65807582990a0a5efddf12de3caea6611173f964de99645e2c02bef138b406ca0644146ae4bb91e0438f8c47beddb0ed22f56bc0851def35824ca6c7258c",
0xe7}], 0x1, &(0x7f0000003b40)}, 0x0)





==================================================================
BUG: KMSAN: uninit-value in ____nf_conntrack_find
net/netfilter/nf_conntrack_core.c:539 [inline]
BUG: KMSAN: uninit-value in __nf_conntrack_find_get+0xc15/0x2190
net/netfilter/nf_conntrack_core.c:573
CPU: 0 PID: 4610 Comm: syz-executor884 Not tainted 4.18.0-rc4+ #24
Hardware name: Google Google Compute Engine/Google Compute Engine,
BIOS Google 01/01/2011
Call Trace:
 __dump_stack lib/dump_stack.c:77 [inline]
 dump_stack+0x185/0x1e0 lib/dump_stack.c:113
 kmsan_report+0x195/0x2c0 mm/kmsan/kmsan.c:1092
 __msan_warning_32+0x7d/0xe0 mm/kmsan/kmsan_instr.c:640
 ____nf_conntrack_find net/netfilter/nf_conntrack_core.c:539 [inline]
 __nf_conntrack_find_get+0xc15/0x2190 net/netfilter/nf_conntrack_core.c:573
 resolve_normal_ct net/netfilter/nf_conntrack_core.c:1331 [inline]
 nf_conntrack_in+0x1674/0x2070 net/netfilter/nf_conntrack_core.c:1416
 ipv6_conntrack_local+0xc3/0xf0
net/ipv6/netfilter/nf_conntrack_l3proto_ipv6.c:179
 nf_hook_entry_hookfn include/linux/netfilter.h:119 [inline]
 nf_hook_slow+0x15d/0x3e0 net/netfilter/core.c:511
 nf_hook include/linux/netfilter.h:242 [inline]
 __ip6_local_out+0x64c/0x770 net/ipv6/output_core.c:164
 ip6_local_out+0xa4/0x1d0 net/ipv6/output_core.c:174
 ip6_send_skb net/ipv6/ip6_output.c:1696 [inline]
 ip6_push_pending_frames+0x218/0x4d0 net/ipv6/ip6_output.c:1716
 rawv6_push_pending_frames net/ipv6/raw.c:616 [inline]
 rawv6_sendmsg+0x45f0/0x5410 net/ipv6/raw.c:935
 inet_sendmsg+0x3fc/0x760 net/ipv4/af_inet.c:798
 sock_sendmsg_nosec net/socket.c:641 [inline]
 sock_sendmsg net/socket.c:651 [inline]
 __sys_sendto+0x798/0x8e0 net/socket.c:1797
 __do_sys_sendto net/socket.c:1809 [inline]
 __se_sys_sendto net/socket.c:1805 [inline]
 __x64_sys_sendto+0x1a1/0x210 net/socket.c:1805
 do_syscall_64+0x15b/0x230 arch/x86/entry/common.c:290
 entry_SYSCALL_64_after_hwframe+0x63/0xe7
RIP: 0033:0x4459c9
Code: e8 bc e7 ff ff 48 83 c4 18 c3 0f 1f 80 00 00 00 00 48 89 f8 48
89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d
01 f0 ff ff 0f 83 2b 0e fc ff c3 66 2e 0f 1f 84 00 00 00 00
RSP: 002b:00007fa03df22d98 EFLAGS: 00000212 ORIG_RAX: 000000000000002c
RAX: ffffffffffffffda RBX: 00000000006dac24 RCX: 00000000004459c9
RDX: 000000000000fedf RSI: 0000000020000000 RDI: 0000000000000004
RBP: 0000000000000000 R08: 0000000020000180 R09: 000000000000001a
R10: 0000000000000000 R11: 0000000000000212 R12: 00000000006dac20
R13: 616e732f7665642f R14: 00007fa03df239c0 R15: 0000000000000001

Uninit was stored to memory at:
 kmsan_save_stack_with_flags mm/kmsan/kmsan.c:256 [inline]
 kmsan_save_stack mm/kmsan/kmsan.c:271 [inline]
 kmsan_internal_chain_origin+0x13c/0x240 mm/kmsan/kmsan.c:683
 __msan_chain_origin+0x76/0xd0 mm/kmsan/kmsan_instr.c:483
 __nf_conntrack_confirm+0x2700/0x3f70 net/netfilter/nf_conntrack_core.c:793
 nf_conntrack_confirm include/net/netfilter/nf_conntrack_core.h:71 [inline]
 ipv6_confirm+0x573/0x740 net/ipv6/netfilter/nf_conntrack_l3proto_ipv6.c:165
 nf_hook_entry_hookfn include/linux/netfilter.h:119 [inline]
 nf_hook_slow+0x15d/0x3e0 net/netfilter/core.c:511
 nf_hook include/linux/netfilter.h:242 [inline]
 NF_HOOK_COND include/linux/netfilter.h:275 [inline]
 ip6_output+0x37d/0x710 net/ipv6/ip6_output.c:171
 dst_output include/net/dst.h:444 [inline]
 ip6_local_out+0x164/0x1d0 net/ipv6/output_core.c:176
 ip6_send_skb net/ipv6/ip6_output.c:1696 [inline]
 ip6_push_pending_frames+0x218/0x4d0 net/ipv6/ip6_output.c:1716
 rawv6_push_pending_frames net/ipv6/raw.c:616 [inline]
 rawv6_sendmsg+0x45f0/0x5410 net/ipv6/raw.c:935
 inet_sendmsg+0x3fc/0x760 net/ipv4/af_inet.c:798
 sock_sendmsg_nosec net/socket.c:641 [inline]
 sock_sendmsg net/socket.c:651 [inline]
 __sys_sendto+0x798/0x8e0 net/socket.c:1797
 __do_sys_sendto net/socket.c:1809 [inline]
 __se_sys_sendto net/socket.c:1805 [inline]
 __x64_sys_sendto+0x1a1/0x210 net/socket.c:1805
 do_syscall_64+0x15b/0x230 arch/x86/entry/common.c:290
 entry_SYSCALL_64_after_hwframe+0x63/0xe7

Uninit was created at:
 kmsan_save_stack_with_flags mm/kmsan/kmsan.c:256 [inline]
 kmsan_internal_poison_shadow+0xc8/0x1d0 mm/kmsan/kmsan.c:181
 kmsan_kmalloc+0xa1/0x120 mm/kmsan/kmsan_hooks.c:91
 kmem_cache_alloc+0xad2/0xbb0 mm/slub.c:2739
 __nf_conntrack_alloc+0x166/0x670 net/netfilter/nf_conntrack_core.c:1137
 init_conntrack+0x635/0x2840 net/netfilter/nf_conntrack_core.c:1219
 resolve_normal_ct net/netfilter/nf_conntrack_core.c:1333 [inline]
 nf_conntrack_in+0x1812/0x2070 net/netfilter/nf_conntrack_core.c:1416
 ipv6_conntrack_local+0xc3/0xf0
net/ipv6/netfilter/nf_conntrack_l3proto_ipv6.c:179
 nf_hook_entry_hookfn include/linux/netfilter.h:119 [inline]
 nf_hook_slow+0x15d/0x3e0 net/netfilter/core.c:511
 nf_hook include/linux/netfilter.h:242 [inline]
 __ip6_local_out+0x64c/0x770 net/ipv6/output_core.c:164
 ip6_local_out+0xa4/0x1d0 net/ipv6/output_core.c:174
 ip6_send_skb net/ipv6/ip6_output.c:1696 [inline]
 ip6_push_pending_frames+0x218/0x4d0 net/ipv6/ip6_output.c:1716
 rawv6_push_pending_frames net/ipv6/raw.c:616 [inline]
 rawv6_sendmsg+0x45f0/0x5410 net/ipv6/raw.c:935
 inet_sendmsg+0x3fc/0x760 net/ipv4/af_inet.c:798
 sock_sendmsg_nosec net/socket.c:641 [inline]
 sock_sendmsg net/socket.c:651 [inline]
 __sys_sendto+0x798/0x8e0 net/socket.c:1797
 __do_sys_sendto net/socket.c:1809 [inline]
 __se_sys_sendto net/socket.c:1805 [inline]
 __x64_sys_sendto+0x1a1/0x210 net/socket.c:1805
 do_syscall_64+0x15b/0x230 arch/x86/entry/common.c:290
 entry_SYSCALL_64_after_hwframe+0x63/0xe7
==================================================================

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