linux-kernel - Re: Question about dev_validate_header used in af

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Date:   Tue, 8 Sep 2020 04:00:13 -0700
From:   Xie He <xie.he.0141@...il.com>
To:     Willem de Bruijn <willemdebruijn.kernel@...il.com>
Cc:     Eric Dumazet <eric.dumazet@...il.com>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Linux Kernel Network Developers <netdev@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: Question about dev_validate_header used in af_packet.c

On Tue, Sep 8, 2020 at 1:41 AM Willem de Bruijn
<willemdebruijn.kernel@...il.com> wrote:
>
> The intent is to bypass such validation to be able to test device
> drivers. Note that removing that may cause someone's test to start
> failing.
>
> >  So there's no point in
> > keeping the ability to test this, either.
>
> I don't disagree in principle, but do note the failing tests. Bar any
> strong reasons for change, I'd leave as is.

OK. I got what you mean. You don't want to make people's test cases fail.

I was recently looking at some drivers, and I felt that if af_packet.c
could help me filter out the invalid RAW frames, I didn't need to
check the validity of the frames myself (in the driver when
transmitting). But now I guess I still need to check that.

I feel this makes the dev_validate_header's variable-length header
check not very useful, because drivers need to do this check again
(when transmitting) anyway.

I was thinking, after I saw dev_validate_header, that we could
eventually make it completely take over the responsibility for a
driver to validate the header when transmitting RAW frames. But now it
seems we would not be able to do this.