netdev - Re: [PATCH RFC net-next] packet: always ensure that we pass hard_header_len bytes in skb

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Message-Id: <20170125.124531.1891159189679013370.davem@davemloft.net>
Date:   Wed, 25 Jan 2017 12:45:31 -0500 (EST)
From:   David Miller <davem@...emloft.net>
To:     sowmini.varadhan@...cle.com
Cc:     netdev@...r.kernel.org
Subject: Re: [PATCH RFC net-next] packet: always ensure that we pass
 hard_header_len bytes in skb_headlen() to the driver

From: Sowmini Varadhan <sowmini.varadhan@...cle.com>
Date: Tue, 24 Jan 2017 08:11:49 -0800

> @@ -2685,21 +2685,22 @@ static inline int dev_parse_header(const struct sk_buff *skb,
>  }
>  
>  /* ll_header must have at least hard_header_len allocated */
> -static inline bool dev_validate_header(const struct net_device *dev,
> +static inline int dev_validate_header(const struct net_device *dev,
>  				       char *ll_header, int len)
>  {
>  	if (likely(len >= dev->hard_header_len))
> -		return true;
> +		return len;
>  
>  	if (capable(CAP_SYS_RAWIO)) {
>  		memset(ll_header + len, 0, dev->hard_header_len - len);
> -		return true;
> +		return dev->hard_header_len;
>  	}
>  
>  	if (dev->header_ops && dev->header_ops->validate)
> -		return dev->header_ops->validate(ll_header, len);
> +		if (!dev->header_ops->validate(ll_header, len))
> +			return -1;
>  
> -	return false;
> +	return dev->hard_header_len;
>  }
>  
>  typedef int gifconf_func_t(struct net_device * dev, char __user * bufptr, int len);

This mostly looks good.  But I'm not so sure you handle the variable length header
case properly.  That's why we have the header_ops->validate() callback, to accomodate
that.

In the variable length case, you'll end up having to return something other than
just hard_header_len.  Probably you'll need to make header_ops->validate() return
that length.