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 19:19:02 -0500
From:   Willem de Bruijn <willemdebruijn.kernel@...il.com>
To:     Sowmini Varadhan <sowmini.varadhan@...cle.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 Fri, Jan 27, 2017 at 4:58 PM, Sowmini Varadhan
<sowmini.varadhan@...cle.com> wrote:
> 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 don't know. An exhaustive search of protocols (by header_ops) may be
needed to say for sure.

If there are none, then the solution indeed is quite simple.

> 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.

Okay. I suspect that there are few, if any. But this is fragile code.