Re: [PATCH] net: Fix potential NULL pointer dereference in __skb_try_recv_datagram

[Jacob Siverskog]

On Tue, Jan 5, 2016 at 3:14 PM, Eric Dumazet <eric.dumazet@xxxxxxxxx> 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@xxxxxxxxx> 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@xxxxxxxxx> wrote:
>> >> > On Wed, Dec 30, 2015 at 6:30 AM, Jacob Siverskog
>> >> > <jacob@xxxxxxxxxxxxxxxxxxx> wrote:
>> >> >> On Wed, Dec 30, 2015 at 2:26 PM, Eric Dumazet <edumazet@xxxxxxxxxx> 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.
>> --
>
> You might build a kernel with KASAN support to get maybe more chances to
> trigger the bug.
>
> ( https://www.kernel.org/doc/Documentation/kasan.txt )
>

Ah. Doesn't seem to be supported on arm(32) unfortunately.
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