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

[Eric Dumazet]

On Wed, 2016-01-20 at 17:17 +0100, Jacob Siverskog wrote:
> On Wed, Jan 20, 2016 at 4:48 PM, Eric Dumazet <eric.dumazet@xxxxxxxxx> wrote:
> > On Wed, 2016-01-20 at 16:06 +0100, Jacob Siverskog wrote:
> >> On Tue, Jan 5, 2016 at 3:39 PM, Eric Dumazet <eric.dumazet@xxxxxxxxx> wrote:
> >> > On Tue, 2016-01-05 at 15:34 +0100, Jacob Siverskog wrote:
> >> >> On Tue, Jan 5, 2016 at 3:14 PM, Eric Dumazet <eric.dumazet@xxxxxxxxx> wrote:
> >> >
> >> >> >
> >> >> > 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.
> >> >
> >> > Then you could at least use standard debugging features :
> >> >
> >> > CONFIG_SLAB=y
> >> > CONFIG_SLABINFO=y
> >> > CONFIG_DEBUG_SLAB=y
> >> > CONFIG_DEBUG_SLAB_LEAK=y
> >> >
> >> > (Or equivalent SLUB options)
> >> >
> >> > and
> >> >
> >> > CONFIG_DEBUG_PAGEALLOC=y
> >> >
> >> > (If arm(32) has CONFIG_ARCH_SUPPORTS_DEBUG_PAGEALLOC=y)
> >>
> >> I tried with those enabled and while toggling power on the Bluetooth
> >> interface I usually get this after a few iterations:
> >> kernel: Bluetooth: Unable to push skb to HCI core(-6)
> >
> > Well, this code seems to be quite buggy.
> >
> > I do not have time to audit it, but 5 minutes are enough to spot 2
> > issues.
> >
> > skb, once given to another queue/layer should not be accessed anymore.
> >
> 
> Ok. Unfortunately I still see the slab corruption even with your changes.

Patch was only showing potential _reads_ after free, which do not
generally corrupt memory.

As I said, a full audit is needed, and I don't have time for this.