linux-kernel - Re: [PATCH] net: Fix potential NULL pointer dereference in __skb_try_recv

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Message-ID: <569FB7F0.6000000@hurleysoftware.com>
Date:	Wed, 20 Jan 2016 08:38:08 -0800
From:	Peter Hurley <peter@...leysoftware.com>
To:	Jacob Siverskog <jacob@...nage.engineering>,
	Eric Dumazet <eric.dumazet@...il.com>
Cc:	Cong Wang <xiyou.wangcong@...il.com>,
	Eric Dumazet <edumazet@...gle.com>,
	David Miller <davem@...emloft.net>,
	Rainer Weikusat <rweikusat@...ileactivedefense.com>,
	netdev <netdev@...r.kernel.org>,
	Herbert Xu <herbert@...dor.apana.org.au>,
	Konstantin Khlebnikov <khlebnikov@...dex-team.ru>,
	Al Viro <viro@...iv.linux.org.uk>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] net: Fix potential NULL pointer dereference in
 __skb_try_recv_datagram

Hi Jacob,

On 01/05/2016 06:34 AM, Jacob Siverskog wrote:
> On Tue, Jan 5, 2016 at 3:14 PM, Eric Dumazet <eric.dumazet@...il.com> wrote:
>> On Tue, 2016-01-05 at 12:07 +0100, Jacob Siverskog wrote:
>>> On Mon, Jan 4, 2016 at 4:25 PM, Eric Dumazet <eric.dumazet@...il.com> wrote:
>>>> On Mon, 2016-01-04 at 10:10 +0100, Jacob Siverskog wrote:
>>>>> On Wed, Dec 30, 2015 at 11:30 PM, Cong Wang <xiyou.wangcong@...il.com> wrote:
>>>>>> On Wed, Dec 30, 2015 at 6:30 AM, Jacob Siverskog
>>>>>> <jacob@...nage.engineering> wrote:
>>>>>>> On Wed, Dec 30, 2015 at 2:26 PM, Eric Dumazet <edumazet@...gle.com> wrote:
>>>>>>>> How often can you trigger this bug ?
>>>>>>>
>>>>>>> Ok. I don't have a good repro to trigger it unfortunately, I've seen it just a
>>>>>>> few times when bringing up/down network interfaces. Does the trace
>>>>>>> give any clue?
>>>>>>>
>>>>>>
>>>>>> A little bit. You need to help people to narrow down the problem
>>>>>> because there are too many places using skb->next and skb->prev.
>>>>>>
>>>>>> Since you mentioned it seems related to network interface flip,
>>>>>> what network interfaces are you using? What's is your TC setup?
>>>>>>
>>>>>> Thanks.
>>>>>
>>>>> The system contains only one physical network interface (TI WL1837,
>>>>> wl18xx module).
>>>>> The state prior to the crash was as follows:
>>>>> - One virtual network interface active (as STA, associated with access point)
>>>>> - Bluetooth (BLE only) active (same physical chip, co-existence,
>>>>> btwilink/st_drv modules)
>>>>>
>>>>> Actions made around the time of the crash:
>>>>> - Bluetooth disabled
>>>>> - One additional virtual network interface brought up (also as STA)
>>>>>
>>>>> I believe the crash occurred between these two actions. I just saw
>>>>> that there are some interesting events in the log prior to the crash:
>>>>> kernel: Bluetooth: Unable to push skb to HCI core(-6)
>>>>> kernel: (stc):  proto stack 4's ->recv failed
>>>>> kernel: (stc): remove_channel_from_table: id 3
>>>>> kernel: (stc): remove_channel_from_table: id 2
>>>>> kernel: (stc): remove_channel_from_table: id 4
>>>>> kernel: (stc):  all chnl_ids unregistered
>>>>> kernel: (stk) :ldisc_install = 0(stc): st_tty_close
>>>>>
>>>>> The first print is from btwilink.c. However, I can't see the
>>>>> connection between Bluetooth (BLE) and UDP/IPv6 (we're not using
>>>>> 6LoWPAN or anything similar).
>>>>>
>>>>> Thanks, Jacob
>>>>
>>>> Definitely these details are useful ;)
>>>>
>>>> Could you try :
>>>>
>>>> diff --git a/drivers/misc/ti-st/st_core.c b/drivers/misc/ti-st/st_core.c
>>>> index 6e3af8b42cdd..0c99a74fb895 100644
>>>> --- a/drivers/misc/ti-st/st_core.c
>>>> +++ b/drivers/misc/ti-st/st_core.c
>>>> @@ -912,7 +912,9 @@ void st_core_exit(struct st_data_s *st_gdata)
>>>>                 skb_queue_purge(&st_gdata->txq);
>>>>                 skb_queue_purge(&st_gdata->tx_waitq);
>>>>                 kfree_skb(st_gdata->rx_skb);
>>>> +               st_gdata->rx_skb = NULL;
>>>>                 kfree_skb(st_gdata->tx_skb);
>>>> +               st_gdata->tx_skb = NULL;
>>>>                 /* TTY ldisc cleanup */
>>>>                 err = tty_unregister_ldisc(N_TI_WL);
>>>>                 if (err)

FWIW,

You don't need that ti-st junk to get the WL1837 working; the WL1837 only
has BT channels. Unfortunately, that's really all I can say about it; sorry.

Regards,
Peter Hurley