[PATCH v2 (resend)] video: fbdev: fix OOB read in vga_8planes_imageblit()

[Tetsuo Handa]

Hello, Greg.

Since nobody is interested in this bug, can you directly pick up
this obvious patch without waiting for maintainer's response?

On 2020/08/31 19:37, Tetsuo Handa wrote:
> syzbot is reporting OOB read at vga_8planes_imageblit() [1], for
> "cdat[y] >> 4" can become a negative value due to "const char *cdat".
> 
> [1] https://syzkaller.appspot.com/bug?id=0d7a0da1557dcd1989e00cb3692b26d4173b4132
> 
> Reported-by: syzbot <syzbot+69fbd3e01470f169c8c4 at syzkaller.appspotmail.com>
> Signed-off-by: Tetsuo Handa <penguin-kernel at I-love.SAKURA.ne.jp>
> ---
>  drivers/video/fbdev/vga16fb.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/video/fbdev/vga16fb.c b/drivers/video/fbdev/vga16fb.c
> index a20eeb8308ff..578d3541e3d6 100644
> --- a/drivers/video/fbdev/vga16fb.c
> +++ b/drivers/video/fbdev/vga16fb.c
> @@ -1121,7 +1121,7 @@ static void vga_8planes_imageblit(struct fb_info *info, const struct fb_image *i
>          char oldop = setop(0);
>          char oldsr = setsr(0);
>          char oldmask = selectmask();
> -        const char *cdat = image->data;
> +	const unsigned char *cdat = image->data;
>  	u32 dx = image->dx;
>          char __iomem *where;
>          int y;
>