Re: [PATCH v4 13/14] rxrpc: Prepare to remove VLA usage for SKCIPHER_REQUEST_ON_STACK

[Arnd Bergmann]

On Wed, Jul 11, 2018 at 10:36 PM, Kees Cook <keescook@xxxxxxxxxxxx> wrote:
> Two uses 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 bumps the affected objects by 20% to silence the warnings while
> still providing coverage is anything grows even more.
>
> Signed-off-by: Kees Cook <keescook@xxxxxxxxxxxx>

(adding David Howells to cc)

I don't think these are in a fast path, it should be possible to just use
skcipher_alloc_req() instead of SKCIPHER_REQUEST_ON_STACK() here.
>From what I can tell, neither of the two are called in atomic context, so
you should be able to use a GFP_KERNEL allocation.

      Arnd