linux-kernel - Re: memory leak in do_ipv6

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Message-ID: <565DB363.6030702@iogearbox.net>
Date:	Tue, 01 Dec 2015 15:49:07 +0100
From:	Daniel Borkmann <daniel@...earbox.net>
To:	Eric Dumazet <eric.dumazet@...il.com>
CC:	Dmitry Vyukov <dvyukov@...gle.com>,
	"David S. Miller" <davem@...emloft.net>,
	Alexey Kuznetsov <kuznet@....inr.ac.ru>,
	James Morris <jmorris@...ei.org>,
	Hideaki YOSHIFUJI <yoshfuji@...ux-ipv6.org>,
	Patrick McHardy <kaber@...sh.net>,
	netdev <netdev@...r.kernel.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Vlad Yasevich <vyasevich@...il.com>,
	Neil Horman <nhorman@...driver.com>,
	linux-sctp@...r.kernel.org, syzkaller <syzkaller@...glegroups.com>,
	Kostya Serebryany <kcc@...gle.com>,
	Alexander Potapenko <glider@...gle.com>,
	Sasha Levin <sasha.levin@...cle.com>,
	Eric Dumazet <edumazet@...gle.com>
Subject: Re: memory leak in do_ipv6_setsockopt

On 12/01/2015 03:38 PM, Eric Dumazet wrote:
> On Tue, 2015-12-01 at 15:24 +0100, Daniel Borkmann wrote:
>> On 12/01/2015 03:16 PM, Eric Dumazet wrote:
>>> On Tue, 2015-12-01 at 15:07 +0100, Daniel Borkmann wrote:
>>>
>>>> Yeah, we miss inet6_destroy_sock() in SCTP. :-(
>>>>
>>>> Looks good to me.
>>>
>>> OK, I will send a formal (and tested ;) ) patch.
>>
>> I was shortly wondering whether there could be a use-after-free by
>> doing this after sctp_destroy_sock() due to the sctp_endpoint_destroy()
>> that would eventually drop a ref on the socket, but the endpoint holds
>> a separate ref, so we should be good.
>
> More generically ->destroy() caller must keep a reference on the socket.
>
> inet_csk_destroy_sock() for example uses sk after
>
> sk->sk_prot->destroy(sk);

Right, and later on, we might call into ->sk_destruct() when there are no
more refs (in SCTP case: sctp_destruct_sock()).

Thanks,
Daniel
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