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Date:   Sat, 4 Jul 2020 18:08:14 +0200
From:   Oscar Carter <oscar.carter@....com>
To:     Kees Cook <keescook@...omium.org>,
        Stefan Richter <stefanr@...6.in-berlin.de>,
        Takashi Sakamoto <o-takashi@...amocchi.jp>
Cc:     kernel-hardening@...ts.openwall.com,
        linux1394-devel@...ts.sourceforge.net,
        linux-kernel@...r.kernel.org, Oscar Carter <oscar.carter@....com>
Subject: Re: [PATCH v3] firewire: Remove function callback casts

Hi,

Anyone has had time to review this patch? Any comments on this?

On Sat, May 30, 2020 at 11:08:39AM +0200, Oscar Carter wrote:
> In 1394 OHCI specification, Isochronous Receive DMA context has several
> modes. One of mode is 'BufferFill' and Linux FireWire stack uses it to
> receive isochronous packets for multiple isochronous channel as
> FW_ISO_CONTEXT_RECEIVE_MULTICHANNEL.
>
> The mode is not used by in-kernel driver, while it's available for
> userspace. The character device driver in firewire-core includes
> cast of function callback for the mode since the type of callback
> function is different from the other modes. The case is inconvenient
> to effort of Control Flow Integrity builds due to
> -Wcast-function-type warning.
>
> This commit removes the cast. A static helper function is newly added
> to initialize isochronous context for the mode. The helper function
> arranges isochronous context to assign specific callback function
> after call of existent kernel API. It's noticeable that the number of
> isochronous channel, speed, and the size of header are not required for
> the mode. The helper function is used for the mode by character device
> driver instead of direct call of existent kernel API.
>
> The same goal can be achieved (in the ioctl_create_iso_context function)
> without this helper function as follows:
> - Call the fw_iso_context_create function passing NULL to the callback
>   parameter.
> - Then setting the context->callback.sc or context->callback.mc
>   variables based on the a->type value.
>
> However using the helper function created in this patch makes code more
> clear and declarative. This way avoid the call to a function with one
> purpose to achieved another one.
>
> Co-developed-by: Takashi Sakamoto <o-takashi@...amocchi.jp>
> Signed-off-by: Takashi Sakamoto <o-takashi@...amocchi.jp>
> Co-developed-by: Stefan Richter <stefanr@...6.in-berlin.de>
> Signed-off-by: Stefan Richter <stefanr@...6.in-berlin.de>
> Signed-off-by: Oscar Carter <oscar.carter@....com>
> ---
> Hi,
>
> this is another proposal to achieved the goal of remove function callback
> cast start by me with the first [1] and second [2] versions, and followed
> by the work of Takashi Sakamoto with his first [3] and second [4] versions,
> and the code of Stefan Richter [5].
>
> The purpose of this third version is to put together all the work done
> until now following the comments of all reviewed patches.
>
> I've added the "Co-developed-by" and "Signed-off-by" tags to give credit to
> Takashi Sakamoto and Stefan Richter if there are no objections.
>
> 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.
>
> Changelog v2->v3
> -Put togeher all the work done in different patches by different authors.
> -Modify the previous work following the comments in the reviewed patches.
>
> [1] https://lore.kernel.org/lkml/20200516173934.31527-1-oscar.carter@gmx.com/
> [2] https://lore.kernel.org/lkml/20200519173425.4724-1-oscar.carter@gmx.com/
> [3] https://lore.kernel.org/lkml/20200520064726.31838-1-o-takashi@sakamocchi.jp/
> [4] https://lore.kernel.org/lkml/20200524132048.243223-1-o-takashi@sakamocchi.jp/
> [5] https://lore.kernel.org/lkml/20200525015532.0055f9df@kant/
>
>  drivers/firewire/core-cdev.c | 32 ++++++++++++++++++++++++++------
>  include/linux/firewire.h     | 11 +++++++----
>  2 files changed, 33 insertions(+), 10 deletions(-)
>
> diff --git a/drivers/firewire/core-cdev.c b/drivers/firewire/core-cdev.c
> index 6e291d8f3a27..f7212331f245 100644
> --- a/drivers/firewire/core-cdev.c
> +++ b/drivers/firewire/core-cdev.c
> @@ -10,6 +10,7 @@
>  #include <linux/delay.h>
>  #include <linux/device.h>
>  #include <linux/dma-mapping.h>
> +#include <linux/err.h>
>  #include <linux/errno.h>
>  #include <linux/firewire.h>
>  #include <linux/firewire-cdev.h>
> @@ -953,11 +954,25 @@ static enum dma_data_direction iso_dma_direction(struct fw_iso_context *context)
>  			return DMA_FROM_DEVICE;
>  }
>
> +static struct fw_iso_context *fw_iso_mc_context_create(struct fw_card *card,
> +						fw_iso_mc_callback_t callback,
> +						void *callback_data)
> +{
> +	struct fw_iso_context *ctx;
> +
> +	ctx = fw_iso_context_create(card, FW_ISO_CONTEXT_RECEIVE_MULTICHANNEL,
> +				    0, 0, 0, NULL, callback_data);
> +	if (!IS_ERR(ctx))
> +		ctx->callback.mc = callback;
> +
> +	return ctx;
> +}
> +
>  static int ioctl_create_iso_context(struct client *client, union ioctl_arg *arg)
>  {
>  	struct fw_cdev_create_iso_context *a = &arg->create_iso_context;
>  	struct fw_iso_context *context;
> -	fw_iso_callback_t cb;
> +	union fw_iso_callback cb;
>  	int ret;
>
>  	BUILD_BUG_ON(FW_CDEV_ISO_CONTEXT_TRANSMIT != FW_ISO_CONTEXT_TRANSMIT ||
> @@ -970,7 +985,7 @@ static int ioctl_create_iso_context(struct client *client, union ioctl_arg *arg)
>  		if (a->speed > SCODE_3200 || a->channel > 63)
>  			return -EINVAL;
>
> -		cb = iso_callback;
> +		cb.sc = iso_callback;
>  		break;
>
>  	case FW_ISO_CONTEXT_RECEIVE:
> @@ -978,19 +993,24 @@ static int ioctl_create_iso_context(struct client *client, union ioctl_arg *arg)
>  		    a->channel > 63)
>  			return -EINVAL;
>
> -		cb = iso_callback;
> +		cb.sc = iso_callback;
>  		break;
>
>  	case FW_ISO_CONTEXT_RECEIVE_MULTICHANNEL:
> -		cb = (fw_iso_callback_t)iso_mc_callback;
> +		cb.mc = iso_mc_callback;
>  		break;
>
>  	default:
>  		return -EINVAL;
>  	}
>
> -	context = fw_iso_context_create(client->device->card, a->type,
> -			a->channel, a->speed, a->header_size, cb, client);
> +	if (a->type == FW_ISO_CONTEXT_RECEIVE_MULTICHANNEL)
> +		context = fw_iso_mc_context_create(client->device->card, cb.mc,
> +						   client);
> +	else
> +		context = fw_iso_context_create(client->device->card, a->type,
> +						a->channel, a->speed,
> +						a->header_size, cb.sc, client);
>  	if (IS_ERR(context))
>  		return PTR_ERR(context);
>  	if (client->version < FW_CDEV_VERSION_AUTO_FLUSH_ISO_OVERFLOW)
> diff --git a/include/linux/firewire.h b/include/linux/firewire.h
> index aec8f30ab200..07967a450eaa 100644
> --- a/include/linux/firewire.h
> +++ b/include/linux/firewire.h
> @@ -436,6 +436,12 @@ typedef void (*fw_iso_callback_t)(struct fw_iso_context *context,
>  				  void *header, void *data);
>  typedef void (*fw_iso_mc_callback_t)(struct fw_iso_context *context,
>  				     dma_addr_t completed, void *data);
> +
> +union fw_iso_callback {
> +	fw_iso_callback_t sc;
> +	fw_iso_mc_callback_t mc;
> +};
> +
>  struct fw_iso_context {
>  	struct fw_card *card;
>  	int type;
> @@ -443,10 +449,7 @@ struct fw_iso_context {
>  	int speed;
>  	bool drop_overflow_headers;
>  	size_t header_size;
> -	union {
> -		fw_iso_callback_t sc;
> -		fw_iso_mc_callback_t mc;
> -	} callback;
> +	union fw_iso_callback callback;
>  	void *callback_data;
>  };
>
> --
> 2.20.1
>

Regards,
Oscar Carter

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