linux-kernel - Re: [PATCH] video: fbdev: arkfb: Cast ics5342

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Message-ID: <b982d4f1-6ed8-490b-8d47-6dc5231913e7@gmx.de>
Date: Sat, 26 Apr 2025 13:32:44 +0200
From: Helge Deller <deller@....de>
To: Kees Cook <kees@...nel.org>
Cc: Javier Martinez Canillas <javierm@...hat.com>,
 Thomas Zimmermann <tzimmermann@...e.de>, Zheyu Ma <zheyuma97@...il.com>,
 Samuel Thibault <samuel.thibault@...-lyon.org>,
 Jiapeng Chong <jiapeng.chong@...ux.alibaba.com>,
 linux-fbdev@...r.kernel.org, dri-devel@...ts.freedesktop.org,
 linux-kernel@...r.kernel.org, linux-hardening@...r.kernel.org
Subject: Re: [PATCH] video: fbdev: arkfb: Cast ics5342_init() allocation type

On 4/26/25 08:23, Kees Cook wrote:
> In preparation for making the kmalloc family of allocators type aware,
> we need to make sure that the returned type from the allocation matches
> the type of the variable being assigned. (Before, the allocator would
> always return "void *", which can be implicitly cast to any pointer type.)
> 
> The assigned type is "struct dac_info *" but the returned type will be
> "struct ics5342_info *", which has a larger allocation size. This is
> by design, as struct ics5342_info contains struct dac_info as its first
> member. Cast the allocation type to match the assignment.
> 
> Signed-off-by: Kees Cook <kees@...nel.org>

Thanks Kees!
I applied your patch, but wouldn't this untested patch be cleaner and fulfill the
same purpose to match a kzalloc return type?

diff --git a/drivers/video/fbdev/arkfb.c b/drivers/video/fbdev/arkfb.c
index 7d131e3d159a..a57c8a992e11 100644
--- a/drivers/video/fbdev/arkfb.c
+++ b/drivers/video/fbdev/arkfb.c
@@ -431,7 +431,8 @@ static struct dac_ops ics5342_ops = {
  
  static struct dac_info * ics5342_init(dac_read_regs_t drr, dac_write_regs_t dwr, void *data)
  {
-       struct dac_info *info = (struct dac_info *)kzalloc(sizeof(struct ics5342_info), GFP_KERNEL);
+       struct ics5342_info *ics_info = kzalloc(sizeof(struct ics5342_info), GFP_KERNEL);
+       struct dac_info *info = &ics_info->dac;
  
         if (! info)


Helge

  ---
> Cc: Helge Deller <deller@....de>
> Cc: Javier Martinez Canillas <javierm@...hat.com>
> Cc: Thomas Zimmermann <tzimmermann@...e.de>
> Cc: Zheyu Ma <zheyuma97@...il.com>
> Cc: Samuel Thibault <samuel.thibault@...-lyon.org>
> Cc: Jiapeng Chong <jiapeng.chong@...ux.alibaba.com>
> Cc: <linux-fbdev@...r.kernel.org>
> Cc: <dri-devel@...ts.freedesktop.org>
> ---
>   drivers/video/fbdev/arkfb.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/video/fbdev/arkfb.c b/drivers/video/fbdev/arkfb.c
> index 082501feceb9..7d131e3d159a 100644
> --- a/drivers/video/fbdev/arkfb.c
> +++ b/drivers/video/fbdev/arkfb.c
> @@ -431,7 +431,7 @@ static struct dac_ops ics5342_ops = {
>   
>   static struct dac_info * ics5342_init(dac_read_regs_t drr, dac_write_regs_t dwr, void *data)
>   {
> -	struct dac_info *info = kzalloc(sizeof(struct ics5342_info), GFP_KERNEL);
> +	struct dac_info *info = (struct dac_info *)kzalloc(sizeof(struct ics5342_info), GFP_KERNEL);
>   
>   	if (! info)
>   		return NULL;