[linux-next] video: fbdev: fbmem: fix pointer reference to null device field

In function do_remove_conflicting_framebuffers, if device is NULL, there
will be null pointer reference. The patch add a check to the if expression.

Signed-off-by: Zhouyi Zhou <zhouzhouyi@gmail.com>
---
Dear Linux folks

I discover this bug in the PowerPC VM provided by
Open source lab of Oregon State University:

https://lkml.org/lkml/2022/2/8/1145

I found that the root cause of null device field is in offb_init_fb:
info = framebuffer_alloc(sizeof(u32) * 16, NULL);

I have tested the patch in the PowerPC VM. Hope my patch can be correct.

Many Thanks
Zhouyi
--
 drivers/video/fbdev/core/fbmem.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

On Thu, Feb 10, 2022 at 02:58:24PM +0800, Zhouyi Zhou wrote:
> In function do_remove_conflicting_framebuffers, if device is NULL, there
> will be null pointer reference. The patch add a check to the if expression.
> 
> Signed-off-by: Zhouyi Zhou <zhouzhouyi@gmail.com>
> ---
> Dear Linux folks
> 
> I discover this bug in the PowerPC VM provided by
> Open source lab of Oregon State University:
> 
> https://lkml.org/lkml/2022/2/8/1145
> 
> I found that the root cause of null device field is in offb_init_fb:
> info = framebuffer_alloc(sizeof(u32) * 16, NULL);
> 
> I have tested the patch in the PowerPC VM. Hope my patch can be correct.

This looks plausible to me, but I am quite unfamiliar with this code.

						Thanx, Paul

> Many Thanks
> Zhouyi
> --
>  drivers/video/fbdev/core/fbmem.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/video/fbdev/core/fbmem.c b/drivers/video/fbdev/core/fbmem.c
> index 34d6bb1bf82e..422b1fc01722 100644
> --- a/drivers/video/fbdev/core/fbmem.c
> +++ b/drivers/video/fbdev/core/fbmem.c
> @@ -1579,7 +1579,7 @@ static void do_remove_conflicting_framebuffers(struct apertures_struct *a,
>  			 * If it's not a platform device, at least print a warning. A
>  			 * fix would add code to remove the device from the system.
>  			 */
> -			if (dev_is_platform(device)) {
> +			if (device && dev_is_platform(device)) {
>  				registered_fb[i]->forced_out = true;
>  				platform_device_unregister(to_platform_device(device));
>  			} else {
> -- 
> 2.25.1
>

Dear Zhouyi,


Am 10.02.22 um 07:58 schrieb Zhouyi Zhou:
> In function do_remove_conflicting_framebuffers, if device is NULL, there
> will be null pointer reference. The patch add a check to the if expression.
> 
> Signed-off-by: Zhouyi Zhou <zhouzhouyi@gmail.com>
> ---
> Dear Linux folks
> 
> I discover this bug in the PowerPC VM provided by
> Open source lab of Oregon State University:
> 
> https://lkml.org/lkml/2022/2/8/1145
> 
> I found that the root cause of null device field is in offb_init_fb:
> info = framebuffer_alloc(sizeof(u32) * 16, NULL);
> 
> I have tested the patch in the PowerPC VM. Hope my patch can be correct.
> 
> Many Thanks
> Zhouyi
> --
>   drivers/video/fbdev/core/fbmem.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/video/fbdev/core/fbmem.c b/drivers/video/fbdev/core/fbmem.c
> index 34d6bb1bf82e..422b1fc01722 100644
> --- a/drivers/video/fbdev/core/fbmem.c
> +++ b/drivers/video/fbdev/core/fbmem.c
> @@ -1579,7 +1579,7 @@ static void do_remove_conflicting_framebuffers(struct apertures_struct *a,
>   			 * If it's not a platform device, at least print a warning. A
>   			 * fix would add code to remove the device from the system.
>   			 */
> -			if (dev_is_platform(device)) {
> +			if (device && dev_is_platform(device)) {
>   				registered_fb[i]->forced_out = true;
>   				platform_device_unregister(to_platform_device(device));
>   			} else {

Looks reasonable.

Acked-by: Paul Menzel <pmenzel@molgen.mpg.de>


Kind regards,

Paul


PS: Please note, this should be unrelated to my problem though, as I 
didn’t use linux-next. (Let’s continue in the other thread though.)