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

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Message-ID: <CAF=yD-+LS6g572Uo5oErq7uazxxPwXXo0w2p4zcHDbXxkuah6Q@mail.gmail.com>
Date:   Fri, 27 Jan 2017 10:28:16 -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

> " The AX.25 device level drivers are simply written to be robust if
>   thrown partial frames.
>    :
>   The other thing that concerns me about this added logic in general is
>   that you are also breaking test tools that want to deliberately send
>   corrupt frames to certain classes of interface."
>
> But how does the driver (even a robust one!) compute the L2 dst/src if the
> application has not even passed down the minimum (which is 21 for ax25?)

Perhaps the goal is to test that the driver gracefully handles such
packets. I can only speculate.

> Would it make sense to only do the CAP_SYS_RAWIO branch if the
> driver declares itself to have variable length L2 headers, via, e.g.,
> some priv flag?

At the time, the comments were not specific to AX25. Again, we should
probably put that bypass behind a flag, enabling validating in the common case.

> BTW the http://comments.gmane.org/gmane.linux.network/401064 referred
> to in commit 2793a23 is not accessible any more, not sure if its contents
> were the same as the link you just shared.

It is. I looked it up in my email archive. Too bad that that seems to
be the only way.