netdev - Re: [PATCH v5 net] stmmac: 802.1ad tag stripping fix

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Date:   Mon, 4 Jun 2018 09:49:58 +0900
From:   Toshiaki Makita <makita.toshiaki@....ntt.co.jp>
To:     David Miller <davem@...emloft.net>, eladv6@...il.com
Cc:     Jose.Abreu@...opsys.com, f.fainelli@...il.com,
        netdev@...r.kernel.org, peppe.cavallaro@...com,
        alexandre.torgue@...com
Subject: Re: [PATCH v5 net] stmmac: 802.1ad tag stripping fix

On 2018/06/03 23:33, David Miller wrote:
> From: Elad Nachman <eladv6@...il.com>
> Date: Wed, 30 May 2018 08:48:25 +0300
> 
>>  static void stmmac_rx_vlan(struct net_device *dev, struct sk_buff *skb)
>>  {
>> -	struct ethhdr *ehdr;
>> +	struct vlan_ethhdr *veth;
>>  	u16 vlanid;
>> +	__be16 vlan_proto;
> 
> Please order local variables from longest to shortest line.
> 
>>  
>> -	if ((dev->features & NETIF_F_HW_VLAN_CTAG_RX) ==
>> -	    NETIF_F_HW_VLAN_CTAG_RX &&
>> -	    !__vlan_get_tag(skb, &vlanid)) {
>> +	if (!__vlan_get_tag(skb, &vlanid)) {
>>  		/* pop the vlan tag */
>> -		ehdr = (struct ethhdr *)skb->data;
>> -		memmove(skb->data + VLAN_HLEN, ehdr, ETH_ALEN * 2);
>> +		veth = (struct vlan_ethhdr *)skb->data;
>> +		vlan_proto = veth->h_vlan_proto;
>> +		memmove(skb->data + VLAN_HLEN, veth, ETH_ALEN * 2);
>>  		skb_pull(skb, VLAN_HLEN);
>> -		__vlan_hwaccel_put_tag(skb, htons(ETH_P_8021Q), vlanid);
>> +		__vlan_hwaccel_put_tag(skb, vlan_proto, vlanid);
>>  	}
>>  }
> 
> I can't see how it is valid to do an unconditional software VLAN
> untagging even when VLAN is disabled in the kernel config or the
> NETIF_F_* feature bits are not set.

Right. It is not valid.

> 
> At a minimum that feature test has to stay there, and when it's clear
> we let the generic VLAN code untag the packet.

Since NETIF_F_HW_VLAN_*_RX are not protocol agnostic, we need two kind
of similar checking here.

veth = (struct vlan_ethhdr *)skb->data;
vlan_proto = veth->h_vlan_proto;
if ((vlan_proto == htons(ETH_P_8021Q) &&
     dev->features & NETIF_F_HW_VLAN_CTAG_RX) ||
    (vlan_proto == htons(ETH_P_8021AD) &&
     dev->features & NETIF_F_HW_VLAN_STAG_RX) {
	vlanid = ntohs(veth->h_vlan_TCI);
	memmove(...);
	skb_pull(...);
	__vlan_hwaccel_put_tag(skb, vlan_proto, vlanid);
}

An alternative way is not to check vlan_proto or features here but
compile this code only when VLAN is enabled in the kernel config. This
can be valid only because this driver does not have NETIF_F_HW_VLAN_*_RX
in hw_features and they can not be toggled for now.

static void stmmac_rx_vlan(struct net_device *dev, struct sk_buff *skb)
{
#ifdef STMMAC_VLAN_TAG_USED
	...
	if (!__vlan_get_tag(skb, &vlanid)) {
		...
		__vlan_hwaccel_put_tag(skb, vlan_proto, vlanid);
	}
#endif
}

-- 
Toshiaki Makita