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Date:   Sun, 24 May 2020 17:23:01 +0200
From:   Greg KH <greg@...ah.com>
To:     Takashi Sakamoto <o-takashi@...amocchi.jp>
Cc:     oscar.carter@....com, keescook@...omium.org,
        stefanr@...6.in-berlin.de, kernel-hardening@...ts.openwall.com,
        linux1394-devel@...ts.sourceforge.net,
        linux-kernel@...r.kernel.org, clemens@...isch.de
Subject: Re: [PATCH v2] firewire-core: remove cast of function callback

On Sun, May 24, 2020 at 10:20:48PM +0900, Takashi Sakamoto 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 inline 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, 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.
> 
> Changes in v2:
>  - unexport helper function
>  - use inline for helper function
>  - arrange arguments for helper function
>  - tested by libhinoko
> 
> Reported-by: Oscar Carter <oscar.carter@....com>
> Reference: https://lore.kernel.org/lkml/20200519173425.4724-1-oscar.carter@gmx.com/
> Signed-off-by: Takashi Sakamoto <o-takashi@...amocchi.jp>
> ---
>  drivers/firewire/core-cdev.c | 40 +++++++++++++++---------------------
>  include/linux/firewire.h     | 16 +++++++++++++++
>  2 files changed, 33 insertions(+), 23 deletions(-)
> 
> diff --git a/drivers/firewire/core-cdev.c b/drivers/firewire/core-cdev.c
> index 6e291d8f3a27..7cbf6df34b43 100644
> --- a/drivers/firewire/core-cdev.c
> +++ b/drivers/firewire/core-cdev.c
> @@ -957,7 +957,6 @@ 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;
>  	int ret;
>  
>  	BUILD_BUG_ON(FW_CDEV_ISO_CONTEXT_TRANSMIT != FW_ISO_CONTEXT_TRANSMIT ||
> @@ -965,32 +964,27 @@ static int ioctl_create_iso_context(struct client *client, union ioctl_arg *arg)
>  		     FW_CDEV_ISO_CONTEXT_RECEIVE_MULTICHANNEL !=
>  					FW_ISO_CONTEXT_RECEIVE_MULTICHANNEL);
>  
> -	switch (a->type) {
> -	case FW_ISO_CONTEXT_TRANSMIT:
> -		if (a->speed > SCODE_3200 || a->channel > 63)
> -			return -EINVAL;
> -
> -		cb = iso_callback;
> -		break;
> -
> -	case FW_ISO_CONTEXT_RECEIVE:
> -		if (a->header_size < 4 || (a->header_size & 3) ||
> -		    a->channel > 63)
> -			return -EINVAL;
> -
> -		cb = iso_callback;
> -		break;
> -
> -	case FW_ISO_CONTEXT_RECEIVE_MULTICHANNEL:
> -		cb = (fw_iso_callback_t)iso_mc_callback;
> -		break;
> +	if (a->type == FW_ISO_CONTEXT_TRANSMIT ||
> +	    a->type == FW_ISO_CONTEXT_RECEIVE) {
> +		if (a->type == FW_ISO_CONTEXT_TRANSMIT) {
> +			if (a->speed > SCODE_3200 || a->channel > 63)
> +				return -EINVAL;
> +		} else {
> +			if (a->header_size < 4 || (a->header_size & 3) ||
> +			    a->channel > 63)
> +				return -EINVAL;
> +		}
>  
> -	default:
> +		context = fw_iso_context_create(client->device->card, a->type,
> +					a->channel, a->speed, a->header_size,
> +					iso_callback, client);
> +	} else if (a->type == FW_ISO_CONTEXT_RECEIVE_MULTICHANNEL) {
> +		context = fw_iso_mc_context_create(client->device->card,
> +						   iso_mc_callback, client);
> +	} else {
>  		return -EINVAL;
>  	}
>  
> -	context = fw_iso_context_create(client->device->card, a->type,
> -			a->channel, a->speed, a->header_size, cb, 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..bff08118baaf 100644
> --- a/include/linux/firewire.h
> +++ b/include/linux/firewire.h
> @@ -453,6 +453,22 @@ struct fw_iso_context {
>  struct fw_iso_context *fw_iso_context_create(struct fw_card *card,
>  		int type, int channel, int speed, size_t header_size,
>  		fw_iso_callback_t callback, void *callback_data);
> +
> +static inline 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;
> +}

Why is this in a .h file?  What's wrong with just putting it in the .c
file as a static function?  There's no need to make this an inline,
right?

thanks,

greg k-h

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