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SubjectRe: WARNING: CPU: 2 PID: 4277 at lib/refcount.c:186
Hi Eric,

I applied your patch and I no longer observed the warning. Thanks! I
will let you know if any further problems show up during fuzzing.

Regards,
Shankara

On Sun, Sep 10, 2017 at 11:34 PM, Eric Dumazet <eric.dumazet@gmail.com> wrote:
> On Fri, 2017-09-08 at 11:46 -0700, Eric Dumazet wrote:
>> On Fri, 2017-09-08 at 10:21 -0700, Cong Wang wrote:
>> > (Cc'ing netdev)
>> >
>> > On Fri, Sep 8, 2017 at 5:59 AM, Shankara Pailoor <sp3485@columbia.edu> wrote:
>> > > Hi,
>> > >
>> > > I found a warning while fuzzing with Syzkaller on linux 4.13-rc7 on
>> > > x86_64. The full stack trace is below:
>> > >
>> > > WARNING: CPU: 2 PID: 4277 at lib/refcount.c:186
>> > > refcount_sub_and_test+0x167/0x1b0 lib/refcount.c:186
>> > > Kernel panic - not syncing: panic_on_warn set ...
>> > >
>> > > CPU: 2 PID: 4277 Comm: syz-executor0 Not tainted 4.13.0-rc7 #3
>> > > Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS
>> > > Ubuntu-1.8.2-1ubuntu1 04/01/2014
>> > > Call Trace:
>> > > <IRQ>
>> > > __dump_stack lib/dump_stack.c:16 [inline]
>> > > dump_stack+0xf7/0x1aa lib/dump_stack.c:52
>> > > panic+0x1ae/0x3a7 kernel/panic.c:180
>> > > __warn+0x1c4/0x1d9 kernel/panic.c:541
>> > > report_bug+0x211/0x2d0 lib/bug.c:183
>> > > fixup_bug+0x40/0x90 arch/x86/kernel/traps.c:190
>> > > do_trap_no_signal arch/x86/kernel/traps.c:224 [inline]
>> > > do_trap+0x260/0x390 arch/x86/kernel/traps.c:273
>> > > do_error_trap+0x118/0x340 arch/x86/kernel/traps.c:310
>> > > do_invalid_op+0x1b/0x20 arch/x86/kernel/traps.c:323
>> > > invalid_op+0x18/0x20 arch/x86/entry/entry_64.S:846
>> > > RIP: 0010:refcount_sub_and_test+0x167/0x1b0 lib/refcount.c:186
>> > > RSP: 0018:ffff88006e006b60 EFLAGS: 00010286
>> > > RAX: 0000000000000026 RBX: 0000000000000000 RCX: 0000000000000000
>> > > RDX: 0000000000000026 RSI: 1ffff1000dc00d2c RDI: ffffed000dc00d60
>> > > RBP: ffff88006e006bf0 R08: 0000000000000001 R09: 0000000000000000
>> > > R10: 0000000000000000 R11: 0000000000000000 R12: 1ffff1000dc00d6d
>> > > R13: 00000000ffffffff R14: 0000000000000001 R15: ffff88006ce9d340
>> > > refcount_dec_and_test+0x1a/0x20 lib/refcount.c:211
>> > > reqsk_put+0x71/0x2b0 include/net/request_sock.h:123
>> > > tcp_v4_rcv+0x259e/0x2e20 net/ipv4/tcp_ipv4.c:1729
>> > > ip_local_deliver_finish+0x2e2/0xba0 net/ipv4/ip_input.c:216
>> > > NF_HOOK include/linux/netfilter.h:248 [inline]
>> > > ip_local_deliver+0x1ce/0x6d0 net/ipv4/ip_input.c:257
>> > > dst_input include/net/dst.h:477 [inline]
>> > > ip_rcv_finish+0x8db/0x19c0 net/ipv4/ip_input.c:397
>> > > NF_HOOK include/linux/netfilter.h:248 [inline]
>> > > ip_rcv+0xc3f/0x17d0 net/ipv4/ip_input.c:488
>> > > __netif_receive_skb_core+0x1fb7/0x31f0 net/core/dev.c:4298
>> > > __netif_receive_skb+0x2c/0x1b0 net/core/dev.c:4336
>> > > process_backlog+0x1c5/0x6d0 net/core/dev.c:5102
>> > > napi_poll net/core/dev.c:5499 [inline]
>> > > net_rx_action+0x6d3/0x14a0 net/core/dev.c:5565
>> > > __do_softirq+0x2cb/0xb2d kernel/softirq.c:284
>> > > do_softirq_own_stack+0x1c/0x30 arch/x86/entry/entry_64.S:898
>> > > </IRQ>
>> > > do_softirq.part.16+0x63/0x80 kernel/softirq.c:328
>> > > do_softirq kernel/softirq.c:176 [inline]
>> > > __local_bh_enable_ip+0x84/0x90 kernel/softirq.c:181
>> > > local_bh_enable include/linux/bottom_half.h:31 [inline]
>> > > rcu_read_unlock_bh include/linux/rcupdate.h:705 [inline]
>> > > ip_finish_output2+0x8ad/0x1360 net/ipv4/ip_output.c:231
>> > > ip_finish_output+0x74e/0xb80 net/ipv4/ip_output.c:317
>> > > NF_HOOK_COND include/linux/netfilter.h:237 [inline]
>> > > ip_output+0x1cc/0x850 net/ipv4/ip_output.c:405
>> > > dst_output include/net/dst.h:471 [inline]
>> > > ip_local_out+0x95/0x160 net/ipv4/ip_output.c:124
>> > > ip_queue_xmit+0x8c6/0x1810 net/ipv4/ip_output.c:504
>> > > tcp_transmit_skb+0x1963/0x3320 net/ipv4/tcp_output.c:1123
>> > > tcp_send_ack.part.35+0x38c/0x620 net/ipv4/tcp_output.c:3575
>> > > tcp_send_ack+0x49/0x60 net/ipv4/tcp_output.c:3545
>> > > tcp_rcv_synsent_state_process net/ipv4/tcp_input.c:5795 [inline]
>> > > tcp_rcv_state_process+0x4876/0x4b60 net/ipv4/tcp_input.c:5930
>> > > tcp_v4_do_rcv+0x58a/0x820 net/ipv4/tcp_ipv4.c:1483
>> > > sk_backlog_rcv include/net/sock.h:907 [inline]
>> > > __release_sock+0x124/0x360 net/core/sock.c:2223
>> > > release_sock+0xa4/0x2a0 net/core/sock.c:2715
>> > > inet_wait_for_connect net/ipv4/af_inet.c:557 [inline]
>> > > __inet_stream_connect+0x671/0xf00 net/ipv4/af_inet.c:643
>> > > inet_stream_connect+0x58/0xa0 net/ipv4/af_inet.c:682
>> > > SYSC_connect+0x204/0x470 net/socket.c:1628
>> > > SyS_connect+0x24/0x30 net/socket.c:1609
>> > > entry_SYSCALL_64_fastpath+0x18/0xad
>> > > RIP: 0033:0x451e59
>> > > RSP: 002b:00007f474843fc08 EFLAGS: 00000216 ORIG_RAX: 000000000000002a
>> > > RAX: ffffffffffffffda RBX: 0000000000718000 RCX: 0000000000451e59
>> > > RDX: 0000000000000010 RSI: 0000000020002000 RDI: 0000000000000007
>> > > RBP: 0000000000000046 R08: 0000000000000000 R09: 0000000000000000
>> > > R10: 0000000000000000 R11: 0000000000000216 R12: 0000000000000000
>> > > R13: 00007ffc040a0f8f R14: 00007f47484409c0 R15: 0000000000000000
>> > >
>> > >
>> > >
>> > >
>> > > I found that the following program is able to reproduce the warning:
>> > >
>> > >
>> > > Pastebin: https://pastebin.com/B75BdYKz
>> > >
>> > > Here are my configs: https://pastebin.com/zRYCXbak
>> > >
>> > > Regards,
>> > > Shankara
>> > >
>>
>> Sweet, thanks for the report, I will have a look.
>>
>> It seems one reqsk_put(req); is missing, but that would lead to a memory
>> leak, not a double reqsk_put(req) :/
>
> OK, it seems the following patch should fix the issue, can you try it ?
>
> (not compiled yet, I will test this tomorrow)
>
> I will have to double check this wont bring other problems :/
>
> Thanks.
>
> diff --git a/net/ipv4/inet_connection_sock.c b/net/ipv4/inet_connection_sock.c
> index 4089c013cb03b12e31ddffbb7ae903542c012ae0..b9c64b40a83af1e151f553ba0e624fae5060ffd0 100644
> --- a/net/ipv4/inet_connection_sock.c
> +++ b/net/ipv4/inet_connection_sock.c
> @@ -916,7 +916,6 @@ static void inet_child_forget(struct sock *sk, struct request_sock *req,
> tcp_sk(child)->fastopen_rsk = NULL;
> }
> inet_csk_destroy_sock(child);
> - reqsk_put(req);
> }
>
> struct sock *inet_csk_reqsk_queue_add(struct sock *sk,
> @@ -987,6 +986,7 @@ void inet_csk_listen_stop(struct sock *sk)
> sock_hold(child);
>
> inet_child_forget(sk, req, child);
> + reqsk_put(req);
> bh_unlock_sock(child);
> local_bh_enable();
> sock_put(child);
>
>

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