linux-hardening - Re: [PATCH][next] firewire: cdev: Fix function cast error

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Date:   Fri, 24 Sep 2021 05:47:47 -0700
From:   Kees Cook <keescook@...omium.org>
To:     "Gustavo A. R. Silva" <gustavoars@...nel.org>,
        Stefan Richter <stefanr@...6.in-berlin.de>
CC:     linux1394-devel@...ts.sourceforge.net,
        linux-kernel@...r.kernel.org, linux-hardening@...r.kernel.org
Subject: Re: [PATCH][next] firewire: cdev: Fix function cast error



On September 24, 2021 3:57:33 AM PDT, "Gustavo A. R. Silva" <gustavoars@...nel.org> wrote:
>Fix the following function cast error when building with
>-Wcast-function-type:
>
>drivers/firewire/core-cdev.c: In function ‘ioctl_create_iso_context’:
>drivers/firewire/core-cdev.c:985:8: error: cast between incompatible function types from ‘void (*)(struct fw_iso_context *, dma_addr_t,  void *)’ {aka ‘void (*)(struct fw_iso_context *, long long unsigned int,  void *)’} to ‘void (*)(struct fw_iso_context *, u32,  size_t,  void *, void *)’ {aka ‘void (*)(struct fw_iso_context *, unsigned int,  long unsigned int,  void *, void *)’} [-Werror=cast-function-type]
>  985 |   cb = (fw_iso_callback_t)iso_mc_callback;
>      |        ^
>cc1: all warnings being treated as errors
>
>This helps with the ongoing efforts to globally enable -Wcast-function-type,
>so when Control Flow Integrity checking lands in the kernel, incompatible
>function type casting doesn't interfere with it.
>
>Link: https://github.com/KSPP/linux/issues/20
>Link: https://github.com/KSPP/linux/issues/102
>Signed-off-by: Gustavo A. R. Silva <gustavoars@...nel.org>

I thought this looked familiar...

https://lore.kernel.org/lkml/20200530090839.7895-1-oscar.carter@gmx.com/

I think someone just needs to pick this up since it got past review, etc.

-Kees


>---
> drivers/firewire/core-cdev.c | 13 ++++++++-----
> 1 file changed, 8 insertions(+), 5 deletions(-)
>
>diff --git a/drivers/firewire/core-cdev.c b/drivers/firewire/core-cdev.c
>index fb6c651214f3..fd2923599667 100644
>--- a/drivers/firewire/core-cdev.c
>+++ b/drivers/firewire/core-cdev.c
>@@ -957,7 +957,10 @@ 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 callback {
>+		fw_iso_callback_t sc;
>+		fw_iso_mc_callback_t mc;
>+	} cb;
> 	int ret;
> 
> 	BUILD_BUG_ON(FW_CDEV_ISO_CONTEXT_TRANSMIT != FW_ISO_CONTEXT_TRANSMIT ||
>@@ -970,7 +973,7 @@ 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:
>@@ -978,11 +981,11 @@ 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:
>@@ -990,7 +993,7 @@ static int ioctl_create_iso_context(struct client *client, union ioctl_arg *arg)
> 	}
> 
> 	context = fw_iso_context_create(client->device->card, a->type,
>-			a->channel, a->speed, a->header_size, cb, client);
>+			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)