ACK: [SRU][J/F/B][PATCH 1/1] video: fbdev: i740fb: Error out if 'pixclock' equals zero

[Cory Todd]

On Fri, Oct 14, 2022 at 10:04:34AM -0500, John Cabaj wrote:
> From: Zheyu Ma <zheyuma97 at gmail.com>
> 
> CVE-2022-3061
> 
> The userspace program could pass any values to the driver through
> ioctl() interface. If the driver doesn't check the value of 'pixclock',
> it may cause divide error.
> 
> Fix this by checking whether 'pixclock' is zero in the function
> i740fb_check_var().
> 
> The following log reveals it:
> 
> divide error: 0000 [#1] PREEMPT SMP KASAN PTI
> RIP: 0010:i740fb_decode_var drivers/video/fbdev/i740fb.c:444 [inline]
> RIP: 0010:i740fb_set_par+0x272f/0x3bb0 drivers/video/fbdev/i740fb.c:739
> Call Trace:
>     fb_set_var+0x604/0xeb0 drivers/video/fbdev/core/fbmem.c:1036
>     do_fb_ioctl+0x234/0x670 drivers/video/fbdev/core/fbmem.c:1112
>     fb_ioctl+0xdd/0x130 drivers/video/fbdev/core/fbmem.c:1191
>     vfs_ioctl fs/ioctl.c:51 [inline]
>     __do_sys_ioctl fs/ioctl.c:874 [inline]
> 
> Signed-off-by: Zheyu Ma <zheyuma97 at gmail.com>
> Signed-off-by: Helge Deller <deller at gmx.de>
> (cherry picked from commit 15cf0b82271b1823fb02ab8c377badba614d95d5)
> Signed-off-by: John Cabaj <john.cabaj at canonical.com>
> ---
>  drivers/video/fbdev/i740fb.c | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/drivers/video/fbdev/i740fb.c b/drivers/video/fbdev/i740fb.c
> index ad5ced4ef972..8fb4e01e1943 100644
> --- a/drivers/video/fbdev/i740fb.c
> +++ b/drivers/video/fbdev/i740fb.c
> @@ -662,6 +662,9 @@ static int i740fb_decode_var(const struct fb_var_screeninfo *var,
>  
>  static int i740fb_check_var(struct fb_var_screeninfo *var, struct fb_info *info)
>  {
> +	if (!var->pixclock)
> +		return -EINVAL;
> +
>  	switch (var->bits_per_pixel) {
>  	case 8:
>  		var->red.offset	= var->green.offset = var->blue.offset = 0;

Acked-by: Cory Todd <cory.todd at canonical.com>

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