[PATCH v4] bridge: fix bridge netlink RCU usage

[PATCH v4] bridge: fix bridge netlink RCU usage

[Johannes Berg]

From: Johannes Berg <johannes.berg@intel.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@intel.com>
---
 net/bridge/br_netlink.c | 14 ++++++++------
 1 file changed, 8 insertions(+), 6 deletions(-)

diff --git a/net/bridge/br_netlink.c b/net/bridge/br_netlink.c
index 3de0eefe2b82..c72083968768 100644
--- a/net/bridge/br_netlink.c
+++ b/net/bridge/br_netlink.c
@@ -81,17 +81,19 @@ static size_t br_get_link_af_size_filtered(const struct net_device *dev,
 	struct net_port_vlans *pv;
 	int num_vlan_infos;
 
+	rcu_read_lock();
 	if (br_port_exists(dev))
-		pv = nbp_get_vlan_info(br_port_get_rtnl(dev));
+		pv = nbp_get_vlan_info(br_port_get_rcu(dev));
 	else if (dev->priv_flags & IFF_EBRIDGE)
 		pv = br_get_vlan_info((struct net_bridge *)netdev_priv(dev));
 	else
-		return 0;
-
-	if (!pv)
-		return 0;
+		pv = NULL;
+	if (pv)
+		num_vlan_infos = br_get_num_vlan_infos(pv, filter_mask);
+	else
+		num_vlan_infos = 0;
+	rcu_read_unlock();
 
-	num_vlan_infos = br_get_num_vlan_infos(pv, filter_mask);
 	if (!num_vlan_infos)
 		return 0;
 
-- 
2.1.4

Re: [PATCH v4] bridge: fix bridge netlink RCU usage

[roopa]

On 3/3/15, 7:02 AM, Johannes Berg wrote:
> From: Johannes Berg <johannes.berg@intel.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@intel.com>
> ---
>   net/bridge/br_netlink.c | 14 ++++++++------
>   1 file changed, 8 insertions(+), 6 deletions(-)
>
> diff --git a/net/bridge/br_netlink.c b/net/bridge/br_netlink.c
> index 3de0eefe2b82..c72083968768 100644
> --- a/net/bridge/br_netlink.c
> +++ b/net/bridge/br_netlink.c
> @@ -81,17 +81,19 @@ static size_t br_get_link_af_size_filtered(const struct net_device *dev,
>   	struct net_port_vlans *pv;
>   	int num_vlan_infos;
>   
> +	rcu_read_lock();
>   	if (br_port_exists(dev))
> -		pv = nbp_get_vlan_info(br_port_get_rtnl(dev));
> +		pv = nbp_get_vlan_info(br_port_get_rcu(dev));
>   	else if (dev->priv_flags & IFF_EBRIDGE)
>   		pv = br_get_vlan_info((struct net_bridge *)netdev_priv(dev));
>   	else
> -		return 0;
> -
> -	if (!pv)
> -		return 0;
> +		pv = NULL;
> +	if (pv)
> +		num_vlan_infos = br_get_num_vlan_infos(pv, filter_mask);
> +	else
> +		num_vlan_infos = 0;
> +	rcu_read_unlock();
>   
> -	num_vlan_infos = br_get_num_vlan_infos(pv, filter_mask);
>   	if (!num_vlan_infos)
>   		return 0;
>   
Acked-by: Roopa Prabhu <roopa@cumulusnetworks.com>

The patch may have to be marked with prefix 'net-next' ?. (unless dave 
infers it from the thread)

Thanks again!

Re: [PATCH v4] bridge: fix bridge netlink RCU usage

[David Miller]

From: Johannes Berg <johannes@sipsolutions.net>
Date: Tue,  3 Mar 2015 16:02:16 +0100

> From: Johannes Berg <johannes.berg@intel.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@intel.com>

Applied to net-next, thanks Johannes.