netdev - Re: [PATCH] bridge: fix bridge netlink RCU usage

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Date:	Tue, 03 Mar 2015 05:40:38 -0800
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Johannes Berg <johannes@...solutions.net>
Cc:	netdev@...r.kernel.org, Roopa Prabhu <roopa@...ulusnetworks.com>,
	Stephen Hemminger <stephen@...workplumber.org>,
	Johannes Berg <johannes.berg@...el.com>
Subject: Re: [PATCH] bridge: fix bridge netlink RCU usage

On Tue, 2015-03-03 at 14:29 +0100, Johannes Berg wrote:
> From: Johannes Berg <johannes.berg@...el.com>
> 
> When the STP timer fires, it can call br_ifinfo_notify(),
> which in turn ends up in the new br_get_link_af_size().
> This function is annotated to be using RTNL locking, which
> clearly isn't the case here, and thus lockdep warns:
> 
>   ===============================
>   [ INFO: suspicious RCU usage. ]
>   3.19.0+ #569 Not tainted
>   -------------------------------
>   net/bridge/br_private.h:204 suspicious rcu_dereference_protected() usage!
> 
> Fix this by doing RCU locking here.
> 
> Fixes: b7853d73e39b ("bridge: add vlan info to bridge setlink and dellink notification messages")
> Signed-off-by: Johannes Berg <johannes.berg@...el.com>
> ---
>  net/bridge/br_netlink.c | 11 +++++++----
>  1 file changed, 7 insertions(+), 4 deletions(-)
> 
> diff --git a/net/bridge/br_netlink.c b/net/bridge/br_netlink.c
> index 17e0177467f5..c63ac0d13add 100644
> --- a/net/bridge/br_netlink.c
> +++ b/net/bridge/br_netlink.c
> @@ -26,12 +26,15 @@ static size_t br_get_link_af_size(const struct net_device *dev)
>  {
>  	struct net_port_vlans *pv;
>  
> -	if (br_port_exists(dev))
> -		pv = nbp_get_vlan_info(br_port_get_rtnl(dev));
> -	else if (dev->priv_flags & IFF_EBRIDGE)
> +	if (br_port_exists(dev)) {
> +		rcu_read_lock();
> +		pv = nbp_get_vlan_info(br_port_get_rcu(dev));
> +		rcu_read_unlock();

right after this rcu_read_unlock(), you no longer are allowed to deref
pv


> +	} else if (dev->priv_flags & IFF_EBRIDGE) {
>  		pv = br_get_vlan_info((struct net_bridge *)netdev_priv(dev));
> -	else
> +	} else {
>  		return 0;
> +	}
>  
>  	if (!pv)
>  		return 0;


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