linux-kernel - Re: [PATCH v2] firewire: Remove function callback casts

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Date:   Wed, 20 May 2020 15:16:24 +0900
From:   Takashi Sakamoto <o-takashi@...amocchi.jp>
To:     Oscar Carter <oscar.carter@....com>
Cc:     Kees Cook <keescook@...omium.org>,
        Stefan Richter <stefanr@...6.in-berlin.de>,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        Clemens Ladisch <clemens@...isch.de>,
        Jaroslav Kysela <perex@...ex.cz>,
        Takashi Iwai <tiwai@...e.com>,
        kernel-hardening@...ts.openwall.com,
        linux1394-devel@...ts.sourceforge.net,
        linux-kernel@...r.kernel.org, linux-media@...r.kernel.org,
        alsa-devel@...a-project.org,
        "Lev R . Oshvang ." <levonshe@...il.com>
Subject: Re: [PATCH v2] firewire: Remove function callback casts

Hi,

On Tue, May 19, 2020 at 07:34:25PM +0200, Oscar Carter wrote:
> In an effort to enable -Wcast-function-type in the top-level Makefile to
> support Control Flow Integrity builds, remove all the function callback
> casts.
> 
> To do this, modify the "fw_iso_context_create" function prototype adding
> a new parameter for the multichannel callback. Also, fix all the
> function calls accordingly.
> 
> In the "fw_iso_context_create" function return an error code if both
> callback parameters are NULL and also set the "ctx->callback.sc"
> explicity to NULL in this case. It is not necessary set to NULL the
> "ctx->callback.mc" variable because this and "ctx->callback.sc" are an
> union and setting one implies setting the other one to the same value.
> 
> Signed-off-by: Oscar Carter <oscar.carter@....com>
> ---
> Changelog v1->v2
> -Set explicity to NULL the "ctx->callback.sc" variable and return an error
>  code in "fw_iso_context_create" function if both callback parameters are
>  NULL as Lev R. Oshvang suggested.
> -Modify the commit changelog accordingly.
> 
>  drivers/firewire/core-cdev.c        | 12 +++++++-----
>  drivers/firewire/core-iso.c         | 14 ++++++++++++--
>  drivers/firewire/net.c              |  2 +-
>  drivers/media/firewire/firedtv-fw.c |  3 ++-
>  include/linux/firewire.h            |  3 ++-
>  sound/firewire/amdtp-stream.c       |  2 +-
>  sound/firewire/isight.c             |  4 ++--
>  7 files changed, 27 insertions(+), 13 deletions(-)

I'm an author of ALSA firewire stack and thanks for the patch. I agree with
your intention to remove the cast of function callback toward CFI build.

Practically, the isochronous context with FW_ISO_CONTEXT_RECEIVE_MULTICHANNEL
is never used by in-kernel drivers. Here, I propose to leave current
kernel API (fw_iso_context_create() with fw_iso_callback_t) as is.
Alternatively, a new kernel API for the context (e.g.
fw_iso_mc_context_create() with fw_iso_mc_callback_t). This idea leaves
current drivers as is and the change is done inner firewire-core driver,
therefore existent kernel API is not changed.

Later I post two patches for the proposal. I'd like you to review it and
I'm glad to receive your comments.


Regards

Takashi Sakamoto