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

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Message-Id: <20160226.123416.1637984479539558683.davem@davemloft.net>
Date:	Fri, 26 Feb 2016 12:34:16 -0500 (EST)
From:	David Miller <davem@...emloft.net>
To:	alan@...ux.intel.com
Cc:	hessu@....iki.fi, netdev@...r.kernel.org, willemb@...gle.com
Subject: Re: Sending short raw packets using sendmsg() broke

From: Alan Cox <alan@...ux.intel.com>
Date: Fri, 26 Feb 2016 14:44:34 +0000

> On Thu, 2016-02-25 at 15:26 -0500, David Miller wrote:
>> From: Heikki Hannikainen <hessu@....iki.fi>
>> Date: Thu, 25 Feb 2016 21:36:07 +0200 (EET)
>> 
>> > Commit 9c7077622dd9174 added a check, ll_header_truncated(), which
>> > requires that a packet transmitted using sendmsg() with PF_PACKET,
>> > SOCK_RAW must be longer than dev->hard_header_len.
>> 
>> Fixed by:
>> 
>> commit 880621c2605b82eb5af91a2c94223df6f5a3fb64
>> Author: Martin Blumenstingl <martin.blumenstingl@...glemail.com>
>> Date:   Sun Nov 22 17:46:09 2015 +0100
>> 
>>     packet: Allow packets with only a header (but no payload)
> 
> The AX.25 case the header is variable length so this still doesn't fix
> the regression as far as I can see.

Then can you suggest a way to ensure that the user has given us a fully
specified link header?  Perhaps we can have a netdev_ops callback for
this, that variable length header technologies can implement.