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

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Date:	Tue, 5 Jan 2016 12:07:29 +0100
From:	Jacob Siverskog <jacob@...nage.engineering>
To:	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

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)
>
>

Sure. Since I don't have a good way to trigger the initial issue, I
can't really know if there is a difference with your patch. However,
normal usage seems to work as expected with your patch. I've tried to
reproduce the initial issue with and without your patch repeatedly for
hours and have not seen any crash in any of the runs so far.
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