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

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Date:	Wed, 20 Jan 2016 09:02:41 -0800
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Jacob Siverskog <jacob@...nage.engineering>
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 Wed, 2016-01-20 at 17:17 +0100, Jacob Siverskog wrote:
> On Wed, Jan 20, 2016 at 4:48 PM, Eric Dumazet <eric.dumazet@...il.com> 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@...il.com> 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@...il.com> 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.