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

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Date:   Fri, 13 Nov 2020 17:40:50 +0200
From:   Nikolay Aleksandrov <nikolay@...dia.com>
To:     Pablo Neira Ayuso <pablo@...filter.org>,
        <netfilter-devel@...r.kernel.org>
CC:     <davem@...emloft.net>, <netdev@...r.kernel.org>, <kuba@...nel.org>,
        <jeremy@...zel.net>
Subject: Re: [PATCH net-next,v3 5/9] bridge: resolve forwarding path for
 bridge devices

On 12/11/2020 02:53, Nikolay Aleksandrov wrote:
> 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@...filter.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.
> 

On a second read this sounds too vague. :) I meant that there are still similar issues in
the bridge code today which I'll take care of. For this patch what I suggested should be enough.

Thanks,
 Nik

>> +	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 = {
>>
>