linux-kernel - Re: [PATCH] net: stmmac: Avoid VLA usage

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Message-ID: <CAGXu5jKrpEOrUVng7zrq0Em9DsAwKfidaqa2AKGrz3ZSXXLn1g@mail.gmail.com>
Date:   Wed, 2 May 2018 05:36:08 -0700
From:   Kees Cook <keescook@...omium.org>
To:     Jose Abreu <Jose.Abreu@...opsys.com>
Cc:     Giuseppe Cavallaro <peppe.cavallaro@...com>,
        Alexandre Torgue <alexandre.torgue@...com>,
        LKML <linux-kernel@...r.kernel.org>,
        Network Development <netdev@...r.kernel.org>
Subject: Re: [PATCH] net: stmmac: Avoid VLA usage

On Wed, May 2, 2018 at 1:54 AM, Jose Abreu <Jose.Abreu@...opsys.com> wrote:
> Hi Kees,
>
> On 01-05-2018 22:01, Kees Cook wrote:
>> In the quest to remove all stack VLAs from the kernel[1], this switches
>> the "status" stack buffer to use the existing small (8) upper bound on
>> how many queues can be checked for DMA, and adds a sanity-check just to
>> make sure it doesn't operate under pathological conditions.
>>
>> [1] https://urldefense.proofpoint.com/v2/url?u=http-3A__lkml.kernel.org_r_CA-2B55aFzCG-2DzNmZwX4A2FQpadafLfEzK6CC-3DqPXydAacU1RqZWA-40mail.gmail.com&d=DwIBAg&c=DPL6_X_6JkXFx7AXWqB0tg&r=WHDsc6kcWAl4i96Vm5hJ_19IJiuxx_p_Rzo2g-uHDKw&m=TBD6a7UY2VbpPmV9LOW_eHAyg8uPq1ZPDhq93VROTVE&s=4fvOST1HhWmZ4lThQe-dHCJYEXNOwey00BCXOWm8tKo&e=
>>
>> Signed-off-by: Kees Cook <keescook@...omium.org>
>>
>
> I rather prefer the variables declaration in reverse-tree order,
> but thats just a minor pick.

I can explicitly reorder the other variables, if you want?

> Reviewed-by: Jose Abreu <joabreu@...opsys.com>

Thanks!

> PS: Is VLA warning switch in gcc already active? Because I didn't
> see this warning in my builds.

It is not. A bunch of people have been building with KCFLAGS=-Wvla to
find the VLAs and sending patches. Once we get rid of them all, we can
add the flag to the top-level Makefile.

-Kees

-- 
Kees Cook
Pixel Security