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

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Date:   Fri, 27 Jan 2017 16:58:48 -0500
From:   Sowmini Varadhan <sowmini.varadhan@...cle.com>
To:     Willem de Bruijn <willemdebruijn.kernel@...il.com>
Cc:     David Miller <davem@...emloft.net>,
        Network Development <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

On (01/27/17 15:51), Willem de Bruijn wrote:
    :
> - limit capable() check to drivers with with .validate callback  
(aka second option below)
    :
> - let privileged applications shoot themselves in the foot (change nothing).

> The second will break variable length header protocols unless
> you exhaustively search for all variable length protocols and add
> validate callbacks first.

other than ax25, are there variable length header protocols out there
without ->validate, and which need the CAP_RAW_SYSIO branch?

I realize that, to an extent, even ethernet is a protocol whose
header is > 14 with vlan, but from the google search, seems like it
was mostly ax25 that really triggered a large part of the check.

If we think that there are a large number of these (that dont have a 
->validate, to fix up things as desired) I'd just go for the "change
nothing in pf_packet" option.

As I found out many drivers like ixgbe and sunvnet have defensive checks
in the Tx path anyway, and xen_netfront can also join that group with
a few simple checks.