netdev - Re: [PATCH] rxrpc: Reuse SKCIPHER_REQUEST_ON

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Date:   Mon, 16 Jul 2018 12:17:50 +0200
From:   Arnd Bergmann <arnd@...db.de>
To:     Kees Cook <keescook@...omium.org>
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 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?

      Arnd