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

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Message-ID: <CAEnXRPsH-eTwwd7FvODL+0Qu9CLY-uGYT9z81cH-by5baEdbhg@mail.gmail.com>
Date:	Mon, 4 Jan 2016 10:10:34 +0100
From:	Jacob Siverskog <jacob@...nage.engineering>
To:	Cong Wang <xiyou.wangcong@...il.com>
Cc:	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

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
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