Re: [PATCH] fbcon: Fix a NULL pointer dereference issue in fbcon_putcs

[Helge Deller <deller@gmx.de>]

On 9/16/24 03:10, Qianqiang Liu wrote:
> syzbot has found a NULL pointer dereference bug in fbcon [1].
>
> This issue is caused by ops->putcs being a NULL pointer.
> We need to check the pointer before using it.
>
> [1] https://syzkaller.appspot.com/bug?extid=3d613ae53c031502687a
>
> Cc: stable@vger.kernel.org
> Reported-and-tested-by: syzbot+3d613ae53c031502687a@syzkaller.appspotmail.com
> Signed-off-by: Qianqiang Liu <qianqiang.liu@163.com>
> ---
>   drivers/video/fbdev/core/fbcon.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/drivers/video/fbdev/core/fbcon.c b/drivers/video/fbdev/core/fbcon.c
> index 3f7333dca508..96c1262cc981 100644
> --- a/drivers/video/fbdev/core/fbcon.c
> +++ b/drivers/video/fbdev/core/fbcon.c
> @@ -1284,7 +1284,7 @@ static void fbcon_putcs(struct vc_data *vc, const u16 *s, unsigned int count,
>   	struct fbcon_display *p = &fb_display[vc->vc_num];
>   	struct fbcon_ops *ops = info->fbcon_par;
>
> -	if (!fbcon_is_inactive(vc, info))
> +	if (!fbcon_is_inactive(vc, info) && ops->putcs)

I think this patch just hides the real problem.
How could putcs have become NULL ?

Helge

>   		ops->putcs(vc, info, s, count, real_y(p, ypos), xpos,
>   			   get_color(vc, info, scr_readw(s), 1),
>   			   get_color(vc, info, scr_readw(s), 0));