netdev - Re: [PATCH 1/2] xfrm: Fix refcount imbalance in xfrm

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Message-ID: <1406156078.3363.20.camel@edumazet-glaptop2.roam.corp.google.com>
Date:	Thu, 24 Jul 2014 00:54:38 +0200
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	David Miller <davem@...emloft.net>
Cc:	steffen.klassert@...unet.com, herbert@...dor.apana.org.au,
	netdev@...r.kernel.org
Subject: Re: [PATCH 1/2] xfrm: Fix refcount imbalance in xfrm_lookup

On Wed, 2014-07-23 at 15:09 -0700, David Miller wrote:
> From: Eric Dumazet <eric.dumazet@...il.com>

> > Hmm... are you sure ?
> > 
> > Before 1a1ccc96abb we did a dst_hold() because we kept the dst in
> > xfrm_policy_sk_bundles. So keeping a reference count was mandatory.
> > 
> > But after, I don't understand why it is needed at all.
> 
> It should be needed.
> 
> We create a new bundle here, from scratch, based upon the socket
> policy.
> 
> Such new bundles make routes with dst refcount == 0.
> 
> All callers expect that the route given back to them is either
> the original 'dst' passed into xfrm_lookup() unmolested, or a
> new 'dst' having a refcount taken for this caller.
> 
> That's why all call sites expect that they can just go
> "dst_release(dst)" and these objects it works.
> 
> So, if we returned 'dst' with refcount == 0 it would not work.

OK, I understood, thanks !


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