Re: [Bridge] [patch net/stable] br: fix use of ->rx_handler_data in code executed on non-rx_handler path

["Michael S. Tsirkin" <mst@redhat.com>]

On Thu, Dec 05, 2013 at 03:50:25PM +0100, Jiri Pirko wrote:
> br_stp_rcv() is reached by non-rx_handler path. That means there is no
> guarantee that dev is bridge port and therefore simple NULL check of
> ->rx_handler_data is not enough. There is need to check if dev is really
> bridge port and since only rcu read lock is held here, do it by checking
> ->rx_handler pointer.
> 
> Note that synchronize_net() in netdev_rx_handler_unregister() ensures
> this approach as valid.
> 
> Introduced originally by:
> commit f350a0a87374418635689471606454abc7beaa3a
>   "bridge: use rx_handler_data pointer to store net_bridge_port pointer"
> 
> Fixed but not in the best way by:
> commit b5ed54e94d324f17c97852296d61a143f01b227a
>   "bridge: fix RCU races with bridge port"
> 
> Reintroduced by:
> commit 716ec052d2280d511e10e90ad54a86f5b5d4dcc2
>   "bridge: fix NULL pointer deref of br_port_get_rcu"
> 
> Please apply to stable trees as well. Thanks.
> 
> Reported-by: Laine Stump <laine@redhat.com>
> Signed-off-by: Jiri Pirko <jiri@resnulli.us>

I would also add:
https://bugzilla.redhat.com/show_bug.cgi?id=1025770

> ---
>  net/bridge/br_private.h  | 12 ++++++++++++
>  net/bridge/br_stp_bpdu.c |  2 +-
>  2 files changed, 13 insertions(+), 1 deletion(-)
> 
> diff --git a/net/bridge/br_private.h b/net/bridge/br_private.h
> index 229d820..67a2d4b 100644
> --- a/net/bridge/br_private.h
> +++ b/net/bridge/br_private.h
> @@ -204,6 +204,13 @@ static inline struct net_bridge_port *br_port_get_rcu(const struct net_device *d
>  	return rcu_dereference(dev->rx_handler_data);
>  }
>  
> +static inline bool br_rx_handler_check_rcu(const struct net_device *dev);

Can't we reorder functions?
Forward-declaring it like this is ugly.

> +
> +static inline struct net_bridge_port *br_port_get_check_rcu(const struct net_device *dev)
> +{
> +	return br_rx_handler_check_rcu(dev) ? br_port_get_rcu(dev) : NULL;
> +}
> +
>  static inline struct net_bridge_port *br_port_get_rtnl(const struct net_device *dev)
>  {
>  	return br_port_exists(dev) ?
> @@ -426,6 +433,11 @@ netdev_features_t br_features_recompute(struct net_bridge *br,
>  int br_handle_frame_finish(struct sk_buff *skb);
>  rx_handler_result_t br_handle_frame(struct sk_buff **pskb);
>  
> +static inline bool br_rx_handler_check_rcu(const struct net_device *dev)
> +{
> +	return rcu_dereference(dev->rx_handler) == br_handle_frame;
> +}
> +
>  /* br_ioctl.c */
>  int br_dev_ioctl(struct net_device *dev, struct ifreq *rq, int cmd);
>  int br_ioctl_deviceless_stub(struct net *net, unsigned int cmd,
> diff --git a/net/bridge/br_stp_bpdu.c b/net/bridge/br_stp_bpdu.c
> index 8660ea3..bdb459d 100644
> --- a/net/bridge/br_stp_bpdu.c
> +++ b/net/bridge/br_stp_bpdu.c
> @@ -153,7 +153,7 @@ void br_stp_rcv(const struct stp_proto *proto, struct sk_buff *skb,
>  	if (buf[0] != 0 || buf[1] != 0 || buf[2] != 0)
>  		goto err;
>  
> -	p = br_port_get_rcu(dev);
> +	p = br_port_get_check_rcu(dev);
>  	if (!p)
>  		goto err;
>  
> -- 
> 1.8.3.1