netdev - Re: BUG: null dereference in __skb_recv

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Date:	Mon, 3 Aug 2015 22:34:02 -0700
From:	Brenden Blanco <bblanco@...mgrid.com>
To:	netdev@...r.kernel.org, herbert@...dor.apana.org.au
Cc:	davem@...emloft.net, khlebnikov@...dex-team.ru
Subject: Re: BUG: null dereference in __skb_recv_datagram

> [  318.244596] BUG: unable to handle kernel NULL pointer dereference
> at 000000000000008e
> [  318.245182] IP: [<ffffffff81455e7c>] __skb_recv_datagram+0xbc/0x5a0

Replying to myself, and adding commit interested parties...

I went through the git log for the function in question, and
positively identified that the following commit introduces the crash:

738ac1e net: Clone skb before setting peeked flag

Null dereference is at line 224 of net/core/datagram.c (according to
my objdump dis-assembly):

                spin_lock_irqsave(&queue->lock, cpu_flags);
                skb_queue_walk(queue, skb) {
                        last = skb;
                        *peeked = skb->peeked;

^-----------------------------------
                        if (flags & MSG_PEEK) {
                                if (_off >= skb->len && (skb->len || _off ||
                                                         skb->peeked)) {

Beyond that, I'm probably out of my comfort zone, so if anyone has a
bright idea of a patch to try, I will gladly test it.
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