netdev - RE: Fix skb_set_peeked use-after-free bug

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Message-ID: <063D6719AE5E284EB5DD2968C1650D6D1CB727D0@AcuExch.aculab.com>
Date:	Tue, 4 Aug 2015 09:24:44 +0000
From:	David Laight <David.Laight@...LAB.COM>
To:	'Herbert Xu' <herbert@...dor.apana.org.au>
CC:	Brenden Blanco <bblanco@...mgrid.com>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	"davem@...emloft.net" <davem@...emloft.net>,
	"khlebnikov@...dex-team.ru" <khlebnikov@...dex-team.ru>
Subject: RE: Fix skb_set_peeked use-after-free bug

From: Herbert Xu
> Sent: 04 August 2015 10:21
> On Tue, Aug 04, 2015 at 09:15:13AM +0000, David Laight wrote:
> >
> > You've introduced a memory leak if skb_clone() fails.
> 
> No I have not.
> 
> > >  	nskb = skb_clone(skb, GFP_ATOMIC);
> > >  	if (!nskb)
> > > -		return -ENOMEM;
> > > +		return ERR_PTR(-ENOMEM);
> >
> > Here the original skb is still allocated.
> >
> > > -				error = skb_set_peeked(skb);
> > > -				if (error)
> > > +				skb = skb_set_peeked(skb);
> >
> > You've now lost the address of the original skb.
> 
> It doesn't matter because we will take the error path and return
> the ENOMEM error.  We must not free the skb as it's still on the
> recv queue.

In that case, what happens to the receive queue when skb_clone()
takes a copy of the skb - freeing the original one?

	David

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