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

[Eric Dumazet <eric.dumazet@gmail.com>]

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@gmail.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@gmail.com> wrote:
> >> > On Wed, Dec 30, 2015 at 6:30 AM, Jacob Siverskog
> >> > <jacob@teenage.engineering> wrote:
> >> >> On Wed, Dec 30, 2015 at 2:26 PM, Eric Dumazet <edumazet@google.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.
> --

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 )