linux-kernel - Re: [PATCH] ppp: mppe: Remove VLA usage

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Message-ID: <CAK8P3a1tph9VPJnYYhBvH_1wZ79wXDvfnJt_CEruj3T-TBG1jg@mail.gmail.com>
Date:   Mon, 16 Jul 2018 13:01:34 +0200
From:   Arnd Bergmann <arnd@...db.de>
To:     Kees Cook <keescook@...omium.org>
Cc:     Paul Mackerras <paulus@...ba.org>,
        "David S. Miller" <davem@...emloft.net>,
        Herbert Xu <herbert@...dor.apana.org.au>,
        Eric Biggers <ebiggers@...gle.com>,
        "Gustavo A. R. Silva" <gustavo@...eddedor.com>,
        linux-ppp@...r.kernel.org, Networking <netdev@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] ppp: mppe: Remove VLA usage

On Mon, Jul 16, 2018 at 6:05 AM, Kees Cook <keescook@...omium.org> wrote:
> In the quest to remove all stack VLA usage from the kernel[1], this
> removes the discouraged use of AHASH_REQUEST_ON_STACK (and associated
> VLA) by switching to shash directly and keeping the associated descriptor
> allocated with the regular state on the heap.
>
> [1] https://lkml.kernel.org/r/CA+55aFzCG-zNmZwX4A2FQpadafLfEzK6CC=qPXydAacU1RqZWA@mail.gmail.com
>
> Signed-off-by: Kees Cook <keescook@...omium.org>

I had concerns at first that this approach might make it slower, but
upon reading through implementation of the shash_ahash_ implementation,
I concluded that it can only be better than before, improving both
performance and stack usage.

Acked-by: Arnd Bergmann <arnd@...db.de>