Re: [PATCH] rxrpc: Reuse SKCIPHER_REQUEST_ON_STACK buffer

[Kees Cook]

On Mon, Jul 16, 2018 at 3:17 AM, Arnd Bergmann <arnd@xxxxxxxx> wrote:
> On Mon, Jul 16, 2018 at 5:49 AM, Kees Cook <keescook@xxxxxxxxxxxx> 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@xxxxxxxxxxxx>
>
> This looks like a very nice solution to the problem.
>
> Acked-by: Arnd Bergmann <arnd@xxxxxxxx>
>
> 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