Attached the Syzkaller C reproducer.
Attachment:
repro.c
Description: Binary data
> On Oct 21, 2020, at 4:57 PM, saeed.mirzamohammadi@xxxxxxxxxx wrote:
>
> From: Saeed Mirzamohammadi <saeed.mirzamohammadi@xxxxxxxxxx>
>
> This patch fixes the issue due to:
>
> [ 89.572883] divide_error: 0000 [#1] SMP KASAN PTI
> [ 89.572897] CPU: 3 PID: 16083 Comm: repro Not tainted 5.9.0-rc7.20200930.rc1.allarch-19-g3e32d0d.syzk #5
> [ 89.572902] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 0.5.1 01/01/2011
> [ 89.572934] RIP: 0010:cirrusfb_check_var+0x84/0x1260
>
> The error happens when the pixels value is calculated before performing the sanity checks on bits_per_pixel.
> A bits_per_pixel set to zero causes divide by zero error.
>
> This patch moves the calculation after the sanity check.
>
> Signed-off-by: Saeed Mirzamohammadi <saeed.mirzamohammadi@xxxxxxxxxx>
> Tested-by: Saeed Mirzamohammadi <saeed.mirzamohammadi@xxxxxxxxxx>
> ---
> drivers/video/fbdev/cirrusfb.c | 3 ++-
> 1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/video/fbdev/cirrusfb.c b/drivers/video/fbdev/cirrusfb.c
> index 15a9ee7cd734..a7749101b094 100644
> --- a/drivers/video/fbdev/cirrusfb.c
> +++ b/drivers/video/fbdev/cirrusfb.c
> @@ -531,7 +531,7 @@ static int cirrusfb_check_var(struct fb_var_screeninfo *var,
> {
> int yres;
> /* memory size in pixels */
> - unsigned pixels = info->screen_size * 8 / var->bits_per_pixel;
> + unsigned int pixels;
> struct cirrusfb_info *cinfo = info->par;
>
> switch (var->bits_per_pixel) {
> @@ -573,6 +573,7 @@ static int cirrusfb_check_var(struct fb_var_screeninfo *var,
> return -EINVAL;
> }
>
> + pixels = info->screen_size * 8 / var->bits_per_pixel;
> if (var->xres_virtual < var->xres)
> var->xres_virtual = var->xres;
> /* use highest possible virtual resolution */
> --
> 2.27.0
>
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