linux-kernel - Re: [PATCH] [NETFILTER] bridge: rcu

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Date:	Mon, 13 Aug 2012 16:36:41 -0700
From:	Stephen Hemminger <shemminger@...tta.com>
To:	Denis Efremov <yefremov.denis@...il.com>
Cc:	Pablo Neira Ayuso <pablo@...filter.org>,
	Patrick McHardy <kaber@...sh.net>,
	netfilter-devel@...r.kernel.org, netfilter@...r.kernel.org,
	coreteam@...filter.org, linux-kernel@...r.kernel.org,
	ldv-project@...ras.ru
Subject: Re: [PATCH] [NETFILTER] bridge: rcu_deref outside read-lock section

On Tue, 14 Aug 2012 02:47:42 +0400
Denis Efremov <yefremov.denis@...il.com> wrote:

> As it noted in the comment before the br_handle_frame_finish
> function, this function should be called under rcu_read_lock.
> 
> The problem callgraph:
> br_dev_xmit -> br_nf_pre_routing_finish_bridge_slow ->
> -> br_handle_frame_finish -> br_port_get_rcu -> rcu_dereference
> 
> And in this case there is no read-lock section.
> I have put lock/unlock in br_nf_pre_routing_finish_bridge_slow,
> as the only function that calls it(for now) - is br_dev_xmit.
> 
> Found by Linux Driver Verification project (linuxtesting.org).
> 
> Signed-off-by: Denis Efremov <yefremov.denis@...il.com>
> ---
>  include/linux/netfilter_bridge.h |    6 +++++-
>  1 files changed, 5 insertions(+), 1 deletions(-)
> 
> diff --git a/include/linux/netfilter_bridge.h b/include/linux/netfilter_bridge.h
> index 31d2844..ceb048e 100644
> --- a/include/linux/netfilter_bridge.h
> +++ b/include/linux/netfilter_bridge.h
> @@ -79,6 +79,7 @@ extern int br_handle_frame_finish(struct sk_buff *skb);
>  /* Only used in br_device.c */
>  static inline int br_nf_pre_routing_finish_bridge_slow(struct sk_buff *skb)
>  {
> +	int res;
>  	struct nf_bridge_info *nf_bridge = skb->nf_bridge;
>  
>  	skb_pull(skb, ETH_HLEN);
> @@ -86,7 +87,10 @@ static inline int br_nf_pre_routing_finish_bridge_slow(struct sk_buff *skb)
>  	skb_copy_to_linear_data_offset(skb, -(ETH_HLEN-ETH_ALEN),
>  				       skb->nf_bridge->data, ETH_HLEN-ETH_ALEN);
>  	skb->dev = nf_bridge->physindev;
> -	return br_handle_frame_finish(skb);
> +	rcu_read_lock();
> +	res = br_handle_frame_finish(skb);
> +	rcu_read_unlock();
> +	return res;
>  }
>  
>  /* This is called by the IP fragmenting code and it ensures there is

Why not just move the rcu_read_lock() in br_dev_xmit earlier?
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