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From: Eric Dumazet <erdlkml@gmail.com>
To: Andrey Konovalov <andreyknvl@google.com>
Cc: syzkaller <syzkaller@googlegroups.com>,
	Dmitry Vyukov <dvyukov@google.com>,
	David Miller <davem@davemloft.net>,
	Tom Herbert <tom@herbertland.com>,
	Alexander Duyck <aduyck@mirantis.com>,
	Hannes Frederic Sowa <hannes@stressinduktion.org>,
	Jiri Benc <jbenc@redhat.com>,
	Sabrina Dubroca <sd@queasysnail.net>,
	netdev <netdev@vger.kernel.org>,
	LKML <linux-kernel@vger.kernel.org>
Subject: Re: net: GPF in eth_header
Date: Sat, 26 Nov 2016 12:05:08 -0800	[thread overview]
Message-ID: <CACPEyM-4dwvmEvq3uTN_8Y-YosP8qA3cYV+oxkufFOn8M+=hew@mail.gmail.com> (raw)
In-Reply-To: <CAAeHK+x48aKLcKfN2aYA1pBPr4Y4ESUvjCTu0xGPoYZuiRbaaw@mail.gmail.com>

> Hi Eric,
>
> The crash happens when the kernel tries to access shadow for nonmapped memory.
>
> The issue here is an integer overflow which happens in neigh_resolve_output().
> skb_network_offset(skb) can return negative number, but __skb_pull()
> accepts unsigned int as len.
> As a result, the least significat bit in higher 32 bits of skb->data
> gets set and we get an out-of-bounds with offset of 4 GB.
>
> I've attached a short reproducer, but you either need KASAN or to add
> a BUG_ON to see the crash.
> In this reproducer skb_network_offset() becomes negative after merging
> two ipv6 fragments.
>
> I actually see multiple places where skb_network_offset() is used as
> an argument to skb_pull().
> So I guess every place can potentially be buggy.

Well, I think the intent is to accept a negative number.

This definitely was assumed by commit e1f165032c8bade authors !

I guess they were using a 32bit kernel for their tests.

  reply	other threads:[~2016-11-26 20:05 UTC|newest]

Thread overview: 19+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2016-11-26 17:30 net: GPF in eth_header Dmitry Vyukov
2016-11-26 18:28 ` Eric Dumazet
2016-11-26 19:07   ` Andrey Konovalov
2016-11-26 20:05     ` Eric Dumazet [this message]
2016-11-26 20:34       ` Eric Dumazet
2016-11-29 10:26       ` Andrey Konovalov
2016-11-29 14:58         ` Eric Dumazet
2016-11-29 15:31           ` Andrey Konovalov
2016-11-29 16:15             ` Eric Dumazet
2016-11-28 18:50     ` Eric Dumazet
2016-11-28 19:04       ` Andrey Konovalov
2016-11-28 19:34         ` Dmitry Vyukov
2016-11-28 19:47           ` Eric Dumazet
2016-11-28 21:05             ` Eric Dumazet
2016-11-28 21:18               ` Eric Dumazet
2016-11-28 21:34                 ` Florian Westphal
2016-11-28 22:14                   ` Eric Dumazet
2016-11-28 22:19                     ` Florian Westphal
2016-11-28 23:16                       ` Eric Dumazet

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