netdev - Re: [PATCH] net: ipv4: current group_info should be put after using.

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Message-ID: <20140411135027.GF15546@mguzik.redhat.com>
Date:	Fri, 11 Apr 2014 15:50:27 +0200
From:	Mateusz Guzik <mguzik@...hat.com>
To:	"Wang, Xiaoming" <xiaoming.wang@...el.com>
Cc:	davem@...emloft.net, kuznet@....inr.ac.ru, jmorris@...ei.org,
	yoshfuji@...ux-ipv6.org, kaber@...sh.net, netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org, chuansheng.liu@...el.com,
	dongxing.zhang@...el.com
Subject: Re: [PATCH] net: ipv4: current group_info should be put after using.

On Fri, Apr 11, 2014 at 10:53:21PM -0400, Wang, Xiaoming wrote:
> This is a typical refcount leak exploitable by unprivileged users.
> Current group_info had been got in ping_init_sock and
> group_info->usage increased. But the usage hasn't decreased
> anywhere in ping. This will make this group_info never freed.
> 

The patch is fine, however I had a brainfart with my last sentence about
commit message, sorry for that.

group_info *can be freed* by malicious user while still being pointed to
by something, that's the biggest problem with refcount leaks, therefore
this message needs some reworking.

I think that discussion about various consequences of refcount leak in
commit message is not necessary.

how about:

Plug a group_info refcount leak in ping_init.

group_info is only needed during initialization and the code failed to
release the reference on exit.

While here move grabbing the reference to a place where it is actually
needed.

====

Please cc: me if you resend the patch.

Thanks,
-- 
Mateusz Guzik
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