Re: [PATCH net-next,v3 5/9] bridge: resolve forwarding path for bridge devices

[Nikolay Aleksandrov <nikolay@nvidia.com>]

On 11/11/2020 21:37, Pablo Neira Ayuso wrote:
> Add .ndo_fill_forward_path for bridge devices.
> 
> Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
> ---
>  include/linux/netdevice.h |  1 +
>  net/bridge/br_device.c    | 24 ++++++++++++++++++++++++
>  2 files changed, 25 insertions(+)
> 
> diff --git a/include/linux/netdevice.h b/include/linux/netdevice.h
> index ca8525a1a797..d26de9a3d382 100644
> --- a/include/linux/netdevice.h
> +++ b/include/linux/netdevice.h
> @@ -836,6 +836,7 @@ typedef u16 (*select_queue_fallback_t)(struct net_device *dev,
>  enum net_device_path_type {
>  	DEV_PATH_ETHERNET = 0,
>  	DEV_PATH_VLAN,
> +	DEV_PATH_BRIDGE,
>  };
>  
>  struct net_device_path {
> diff --git a/net/bridge/br_device.c b/net/bridge/br_device.c
> index 387403931a63..4c3a5334abe0 100644
> --- a/net/bridge/br_device.c
> +++ b/net/bridge/br_device.c
> @@ -391,6 +391,29 @@ static int br_del_slave(struct net_device *dev, struct net_device *slave_dev)
>  	return br_del_if(br, slave_dev);
>  }
>  
> +static int br_fill_forward_path(struct net_device_path_ctx *ctx,
> +				struct net_device_path *path)
> +{
> +	struct net_bridge_fdb_entry *f;
> +	struct net_bridge_port *dst;
> +	struct net_bridge *br;
> +
> +	if (netif_is_bridge_port(ctx->dev))
> +		return -1;
> +
> +	br = netdev_priv(ctx->dev);
> +	f = br_fdb_find_rcu(br, ctx->daddr, 0);
> +	if (!f || !f->dst)
> +		return -1;
> +
> +	dst = READ_ONCE(f->dst);

While this is ok, I meant that you have to test the ptr after. In theory between
the !f->dst test above and now it could've become null, so to make it future-proof
please test the null dst after deref, after the READ_ONCE(). I realize currently
there are still problems after the change but we'll fix them.

> +	path->type = DEV_PATH_BRIDGE;
> +	path->dev = dst->br->dev;
> +	ctx->dev = dst->dev;
> +
> +	return 0;
> +}
> +
>  static const struct ethtool_ops br_ethtool_ops = {
>  	.get_drvinfo		 = br_getinfo,
>  	.get_link		 = ethtool_op_get_link,
> @@ -425,6 +448,7 @@ static const struct net_device_ops br_netdev_ops = {
>  	.ndo_bridge_setlink	 = br_setlink,
>  	.ndo_bridge_dellink	 = br_dellink,
>  	.ndo_features_check	 = passthru_features_check,
> +	.ndo_fill_forward_path	 = br_fill_forward_path,
>  };
>  
>  static struct device_type br_type = {
>