Date:   Mon, 24 Jul 2017 20:21:16 -0700
From:   Kees Cook <keescook@...omium.org>
To:     Hans Liljestrand <liljestrandh@...il.com>
Cc:     "Reshetova, Elena" <elena.reshetova@...el.com>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        LKML <linux-kernel@...r.kernel.org>, LKP <lkp@...org>
Subject: Re: [lkp-robot] [x86/refcount] b631e535c6: WARNING:at_net/netlink/af_netlink.c:#netlink_sock_destruct

On Mon, Jul 24, 2017 at 6:03 AM, Hans Liljestrand
<liljestrandh@...il.com> wrote:
> On Sun, Jul 23, 2017 at 08:52:53PM -0700, Kees Cook wrote:
>>
>> Is 14afee4b6092f ("net: convert sock.sk_wmem_alloc from atomic_t to
>> refcount_t") correct? That looks like a statistics counter, not a
>> refcounter? I can't quite tell, though...
>
>
> Hmm, yes, it looks a bit weird, but it is used in a refcount fashion here:
>
> void sk_free(struct sock *sk)
> {
>         /*
>          * We subtract one from sk_wmem_alloc and can know if
>          * some packets are still in some tx queue.
>          * If not null, sock_wfree() will call __sk_free(sk) later
>          */
>         if (refcount_dec_and_test(&sk->sk_wmem_alloc))
>                 __sk_free(sk);
> }
> http://elixir.free-electrons.com/linux/v4.13-rc1/source/net/core/sock.c#L1605

Ah yeah, there it is. Hrmpf. Something is triggering WARNs, though...
I wonder if this can get examined more closely?

Also, why not atomic->refcount for sk_rmem_alloc?

-Kees

>
> And here:
>
>         if (refcount_sub_and_test(len, &sk->sk_wmem_alloc))
>                 __sk_free(sk);
> }
> http://elixir.free-electrons.com/linux/v4.13-rc1/source/net/core/sock.c#L1798
>
>>
>> I think this WARN is from:
>>
>> WARN_ON(refcount_read(&sk->sk_wmem_alloc));
>
>
> I looked through the commit and couldn't find any direct conversion issues.
> Although I guess it is debatable whether refcoun_t should be used in this
> kind of less conventional case.
>
> The only potential problem I noticed was that based on the following change
> (or rather the original code) it seems like sk_wmem_alloc could sometimes be
> negative. I'm not familiar enough with the code to say whether that really
> is the case.
>
> --- a/drivers/atm/fore200e.c
> +++ b/drivers/atm/fore200e.c
> @@ -924,12 +924,7 @@ fore200e_tx_irq(struct fore200e* fore200e)
>                else {
>                    dev_kfree_skb_any(entry->skb);
>                }
> -#if 1
> -               /* race fixed by the above incarnation mechanism, but... */
> -               if (atomic_read(&sk_atm(vcc)->sk_wmem_alloc) < 0) {
> -                   atomic_set(&sk_atm(vcc)->sk_wmem_alloc, 0);
> -               }
> -#endif
> +
>                /* check error condition */
>                if (*entry->status & STATUS_ERROR)
>                    atomic_inc(&vcc->stats->tx_err);
>
> But if this is actually supposed to legitimately happen and eventually
> "balance out" refcount_t might not work here. On the other hand this should
> have triggered an earlier WARN_ON already, so it doesn't seem to be the
> issue here?
>
> Regards,
> -hans
>
>
>>
>> -Kees
>>
>> On Sun, Jul 23, 2017 at 7:13 PM, kernel test robot
>> <xiaolong.ye@...el.com> wrote:
>>>
>>>
>>> FYI, we noticed the following commit:
>>>
>>> commit: b631e535c61d7ddbb7ebac545f729ca9b3b6d70e ("x86/refcount:
>>> Implement fast refcount overflow protection")
>>> https://git.kernel.org/cgit/linux/kernel/git/kees/linux.git
>>> kspp/fast-refcount/ud/v6
>>>
>>> in testcase: boot
>>>
>>> on test machine: qemu-system-x86_64 -enable-kvm -smp 2 -m 512M
>>>
>>> caused below changes (please refer to attached dmesg/kmsg for entire
>>> log/backtrace):
>>>
>>>
>>>
>>> +------------------------------------------------------------+------------+------------+
>>> |                                                            | 561ee9566e
>>> | b631e535c6 |
>>>
>>> +------------------------------------------------------------+------------+------------+
>>> | boot_successes                                             | 37
>>> | 0          |
>>> | boot_failures                                              | 0
>>> | 4          |
>>> | WARNING:at_net/netlink/af_netlink.c:#netlink_sock_destruct | 0
>>> | 4          |
>>>
>>> +------------------------------------------------------------+------------+------------+
>>>
>>>
>>>
>>> [   36.991339] WARNING: CPU: 0 PID: 280 at net/netlink/af_netlink.c:374
>>> netlink_sock_destruct+0x1ea/0x200
>>> [   36.994035] Modules linked in:
>>> [   36.994815] CPU: 0 PID: 280 Comm: sh Not tainted
>>> 4.13.0-rc1-00003-gb631e53 #1
>>> [   36.996546] task: ffff88001448c180 task.stack: ffffc900004e0000
>>> [   36.998006] RIP: 0010:netlink_sock_destruct+0x1ea/0x200
>>> [   36.999290] RSP: 0018:ffffffff82433de0 EFLAGS: 00010206
>>> [   37.000591] RAX: ffff88001448c180 RBX: ffff880016a3d000 RCX:
>>> 0000000000000000
>>> [   37.002319] RDX: 0000000000000100 RSI: 0000000000000001 RDI:
>>> ffffffff82796f48
>>> [   37.004061] RBP: ffffffff82433df0 R08: 0000000000000000 R09:
>>> 0000000000000000
>>> [   37.005780] R10: 0000000000000001 R11: 0000000000000001 R12:
>>> 0000000000000001
>>> [   37.007528] R13: ffffffff81cd4a00 R14: 96e49674e09954cf R15:
>>> 000000000000001f
>>> [   37.009261] FS:  0000000000000000(0000) GS:ffffffff82430000(0000)
>>> knlGS:0000000000000000
>>> [   37.011233] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
>>> [   37.012629] CR2: 00007f268a96e688 CR3: 00000000159ff000 CR4:
>>> 00000000000006b0
>>> [   37.014212] Call Trace:
>>> [   37.014745]  <IRQ>
>>> [   37.015201]  __sk_destruct+0x3a2/0x4c0
>>> [   37.015994]  sk_destruct+0x3f/0x70
>>> [   37.016747]  __sk_free+0x10d/0x160
>>> [   37.017479]  sk_free+0x4a/0x60
>>> [   37.018127]  deferred_put_nlk_sk+0xd9/0xf0
>>> [   37.018998]  rcu_process_callbacks+0x766/0x1cb0
>>> [   37.019944]  ? rcu_process_callbacks+0x643/0x1cb0
>>> [   37.020960]  __do_softirq+0x10c/0x6b2
>>> [   37.021749]  irq_exit+0x135/0x140
>>> [   37.022458]  smp_apic_timer_interrupt+0x3b/0x50
>>> [   37.023429]  apic_timer_interrupt+0x8e/0xa0
>>> [   37.024303] RIP: 0010:__sanitizer_cov_trace_pc+0x0/0x60
>>> [   37.025141] RSP: 0018:ffffc900004e3c10 EFLAGS: 00000246 ORIG_RAX:
>>> ffffffffffffff10
>>> [   37.026605] RAX: ffff88001448c180 RBX: ffffffff82727288 RCX:
>>> 0000000000000000
>>> [   37.028340] RDX: 0000000000000000 RSI: 0000000000000000 RDI:
>>> ffffffff82727288
>>> [   37.030077] RBP: ffffc900004e3c60 R08: 0000000000000000 R09:
>>> 0000000000000000
>>> [   37.031796] R10: 0000000000000000 R11: 0000000000000001 R12:
>>> 0000000000000000
>>> [   37.033546] R13: 0000000000000000 R14: 0000000000000000 R15:
>>> 00007f2689f93000
>>> [   37.035262]  </IRQ>
>>> [   37.035814]  ? ftrace_likely_update+0x39/0x200
>>> [   37.036925]  ? vm_normal_page+0xd7/0x1a0
>>> [   37.037886]  unmap_page_range+0x775/0x14d0
>>> [   37.038658]  unmap_single_vma+0x158/0x180
>>> [   37.039403]  unmap_vmas+0x5b/0x80
>>> [   37.040202]  exit_mmap+0x118/0x220
>>> [   37.040900]  mmput+0xd5/0x240
>>> [   37.041479]  do_exit+0xdb6/0x16d0
>>> [   37.042183]  ? entry_SYSCALL_64_fastpath+0x5/0xbd
>>> [   37.043365]  do_group_exit+0x8a/0x160
>>> [   37.044282]  SyS_exit_group+0x1d/0x20
>>> [   37.045192]  entry_SYSCALL_64_fastpath+0x1f/0xbd
>>> [   37.046321] RIP: 0033:0x7f268a676408
>>> [   37.047221] RSP: 002b:00007ffcba052ea8 EFLAGS: 00000246 ORIG_RAX:
>>> 00000000000000e7
>>> [   37.049042] RAX: ffffffffffffffda RBX: 000000000000007f RCX:
>>> 00007f268a676408
>>> [   37.050784] RDX: 000000000000007f RSI: 000000000000003c RDI:
>>> 000000000000007f
>>> [   37.052512] RBP: 00007f268a96e688 R08: 00000000000000e7 R09:
>>> ffffffffffffffa0
>>> [   37.054281] R10: 0000000000000000 R11: 0000000000000246 R12:
>>> 00007f268a96ff40
>>> [   37.056004] R13: 0000000000000001 R14: 0000000000000000 R15:
>>> 00000000ffffffff
>>> [   37.057765] Code: e8 56 14 48 ff eb ca e8 b5 42 4f ff 0f ff 0f 1f 00
>>> eb a7 e8 a9 42 4f ff 0f ff 0f 1f 80 00 00 00 00 e9 48 ff ff ff e8 96 42 4f
>>> ff <0f> ff 0f 1f 40 00 e9 e5 fe ff ff 90 66 2e 0f 1f 84 00 00 00 00
>>> [   37.062621] ---[ end trace db04ba531557bbda ]---
>>>
>>>
>>> To reproduce:
>>>
>>>         git clone https://github.com/01org/lkp-tests.git
>>>         cd lkp-tests
>>>         bin/lkp qemu -k <bzImage> job-script  # job-script is attached in
>>> this email
>>>
>>>
>>>
>>> Thanks,
>>> Xiaolong
>>
>>
>>
>>
>> --
>> Kees Cook
>> Pixel Security



-- 
Kees Cook
Pixel Security

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