netdev - Re: Sending short raw packets using sendmsg() broke

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Date:	Fri, 26 Feb 2016 12:46:45 -0500 (EST)
From:	David Miller <davem@...emloft.net>
To:	willemdebruijn.kernel@...il.com
Cc:	alan@...ux.intel.com, hessu@....iki.fi, netdev@...r.kernel.org,
	willemb@...gle.com
Subject: Re: Sending short raw packets using sendmsg() broke

From: Willem de Bruijn <willemdebruijn.kernel@...il.com>
Date: Fri, 26 Feb 2016 12:33:13 -0500

> Right. The simplest, if hacky, fix is to add something along the lines of
> 
>   static unsigned short netdev_min_hard_header_len(struct net_device *dev)
>   {
>       if (unlikely(dev->type ==ARPHDR_AX25))
>         return AX25_KISS_HEADER_LEN;
>       else
>         return dev->hard_header_len;
>   }
> 
> Depending on how the variable encoding scheme works, a basic min
> length check may still produce buggy headers that confuse the stack or
> driver. I need to read up on AX25. If so, then extending header_ops
> with an optional validate() function is a more generic approach of
> checking header sanity.

I suspect we will need some kind of header ops for this.