netdev - Re: [PATCH] rxrpc: Reuse SKCIPHER_REQUEST_ON

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Message-ID: <CAGXu5j+PirJXbeaawd0gXc-NfWBtS4-9tR85=XTQ0+oFdC8XuA@mail.gmail.com>
Date:   Wed, 18 Jul 2018 21:29:38 -0700
From:   Kees Cook <keescook@...omium.org>
To:     Arnd Bergmann <arnd@...db.de>
Cc:     David Howells <dhowells@...hat.com>,
        Herbert Xu <herbert@...dor.apana.org.au>,
        Eric Biggers <ebiggers@...gle.com>,
        "Gustavo A. R. Silva" <gustavo@...eddedor.com>,
        "David S. Miller" <davem@...emloft.net>,
        Networking <netdev@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] rxrpc: Reuse SKCIPHER_REQUEST_ON_STACK buffer

On Mon, Jul 16, 2018 at 3:17 AM, Arnd Bergmann <arnd@...db.de> wrote:
> On Mon, Jul 16, 2018 at 5:49 AM, Kees Cook <keescook@...omium.org> wrote:
>> The use of SKCIPHER_REQUEST_ON_STACK() will trigger FRAME_WARN warnings
>> (when less than 2048) once the VLA is no longer hidden from the check:
>>
>> net/rxrpc/rxkad.c:398:1: warning: the frame size of 1152 bytes is larger than 1024 bytes [-Wframe-larger-than=]
>> net/rxrpc/rxkad.c:242:1: warning: the frame size of 1152 bytes is larger than 1024 bytes [-Wframe-larger-than=]
>>
>> This passes the initial SKCIPHER_REQUEST_ON_STACK allocation to the leaf
>> functions for reuse. Two requests allocated on the stack are not needed
>> when only one is used at a time.
>>
>> Signed-off-by: Kees Cook <keescook@...omium.org>
>
> This looks like a very nice solution to the problem.
>
> Acked-by: Arnd Bergmann <arnd@...db.de>
>
> Since the large stack usage could already cause problems in older kernels,
> should this be backported to stable kernels as well?

I don't think this hits the bar for doing a -stable patch, but if you
think I should, I can do it.

-Kees

-- 
Kees Cook
Pixel Security