netdev - Re: [PATCH net] 6lowpan: fix double free in lowpan_frag

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Date: Fri, 6 Oct 2023 07:07:34 +0300
From: Dan Carpenter <dan.carpenter@...aro.org>
To: Alexander Aring <aahringo@...hat.com>
Cc: Alexander Aring <alex.aring@...il.com>,
	Stefan Schmidt <stefan@...enfreihafen.org>,
	Miquel Raynal <miquel.raynal@...tlin.com>,
	"David S. Miller" <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>,
	Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>,
	Angus Chen <angus.chen@...uarmicro.com>,
	Luis Chamberlain <mcgrof@...nel.org>,
	Joel Granados <joel.granados@...il.com>, linux-wpan@...r.kernel.org,
	netdev@...r.kernel.org, kernel-janitors@...r.kernel.org
Subject: Re: [PATCH net] 6lowpan: fix double free in lowpan_frag_rcv()

On Thu, Oct 05, 2023 at 06:10:13PM -0400, Alexander Aring wrote:
> Hi,
> 
> On Wed, Oct 4, 2023 at 5:22 AM Dan Carpenter <dan.carpenter@...aro.org> wrote:
> >
> > The skb() is freed by the caller in lowpan_invoke_rx_handlers() so this
> > free is a double free.
> >
> 
> lowpan_frag_rcv() does not call lowpan_invoke_rx_handlers(), it calls
> lowpan_invoke_frag_rx_handlers(), or is there something I overlooked
> here?

Actually now that I look at it more closely this isn't a bug.

The way I was looking at it was that it was the other way around.
lowpan_invoke_rx_handlers() is the caller.  But actually this returns
-1.  lowpan_invoke_rx_handlers() will pass the freed skb to
lowpan_rx_handlers_result() but the -1 gets translated to RX_DROP in
lowpan_rx_h_frag() then it just returns NET_RX_DROP.  It's a no-op and
not a double free.

Sorry!

regards,
dan carpenter