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

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Date:	Wed, 20 Jan 2016 16:06:55 +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 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)
kernel: (stc):  proto stack 4's ->recv failed
kernel: Slab corruption (Not tainted): skbuff_head_cache start=c08a8a00, len=176
kernel: 0a0: 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6a 6b 6b a5  kkkkkkkkkkkkjkk.
kernel: Prev obj: start=c08a8940, len=176
kernel: 000: 00 00 00 00 00 00 00 00 31 73 52 00 43 17 2b 14  ........1sR.C.+.
kernel: 010: 00 00 00 00 00 00 00 00 04 00 00 00 01 00 00 00  ................
kernel: Next obj: start=c08a8ac0, len=176
kernel: 000: 00 00 00 00 00 00 00 00 01 42 f6 50 36 17 2b 14  .........B.P6.+.
kernel: 010: 00 00 00 00 00 00 00 00 04 00 00 00 01 00 00 00  ................

The "Unable to push skb" and "recv failed" lines always appear before
the corruption.

Unfortunately, the corruptions occur also with your patch.