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

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Date:	Wed, 23 Jul 2014 19:21:13 +0200
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Steffen Klassert <steffen.klassert@...unet.com>
Cc:	David Miller <davem@...emloft.net>,
	Herbert Xu <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 10:18 +0200, Steffen Klassert wrote:
> xfrm_lookup must return a dst_entry with a refcount for the caller.
> Git commit 1a1ccc96abb ("xfrm: Remove caching of xfrm_policy_sk_bundles")
> removed this refcount for the socket policy case accidentally.
> This patch restores it and sets DST_NOCACHE flag to make sure
> that the dst_entry is freed when the refcount becomes null.
> 
> Fixes: 1a1ccc96abb ("xfrm: Remove caching of xfrm_policy_sk_bundles")
> Signed-off-by: Steffen Klassert <steffen.klassert@...unet.com>
> ---
>  net/xfrm/xfrm_policy.c | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/net/xfrm/xfrm_policy.c b/net/xfrm/xfrm_policy.c
> index a8ef510..0525d78 100644
> --- a/net/xfrm/xfrm_policy.c
> +++ b/net/xfrm/xfrm_policy.c
> @@ -2097,6 +2097,8 @@ struct dst_entry *xfrm_lookup(struct net *net, struct dst_entry *dst_orig,
>  				goto no_transform;
>  			}
>  
> +			dst_hold(&xdst->u.dst);
> +			xdst->u.dst.flags |= DST_NOCACHE;
>  			route = xdst->route;
>  		}
>  	}


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.



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