[PATCH 1/1] fbmem: add margin check to fb_check_caps()

[PATCH 1/1] fbmem: add margin check to fb_check_caps()

[George Kennedy]

A fb_ioctl() FBIOPUT_VSCREENINFO call with invalid xres setting
or yres setting in struct fb_var_screeninfo will result in a
KASAN: vmalloc-out-of-bounds failure in bitfill_aligned() as
the margins are being cleared. The margins are cleared in
chunks and if the xres setting or yres setting is a value of
zero upto the chunk size, the failure will occur.

Add a margin check to validate xres and yres settings.

Signed-off-by: George Kennedy <george.kennedy@oracle.com>
Suggested-by: Dan Carpenter <dan.carpenter@oracle.com>
Reported-by: syzbot+e5fd3e65515b48c02a30@syzkaller.appspotmail.com
---
 drivers/video/fbdev/core/fbmem.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/drivers/video/fbdev/core/fbmem.c b/drivers/video/fbdev/core/fbmem.c
index 30e73ec..cd50302 100644
--- a/drivers/video/fbdev/core/fbmem.c
+++ b/drivers/video/fbdev/core/fbmem.c
@@ -1007,6 +1007,10 @@ static int fb_check_caps(struct fb_info *info, struct fb_var_screeninfo *var,
 		return 0;
 	}
 
+	/* bitfill_aligned() assumes that it's at least 8x8 */
+	if (var->xres < 8 || var->yres < 8)
+		return -EINVAL;
+
 	ret = info->fbops->fb_check_var(var, info);
 
 	if (ret)
-- 
1.8.3.1

Re: [PATCH 1/1] fbmem: add margin check to fb_check_caps()

[Dan Carpenter]

On Tue, Jul 07, 2020 at 03:26:03PM -0400, George Kennedy wrote:
> A fb_ioctl() FBIOPUT_VSCREENINFO call with invalid xres setting
> or yres setting in struct fb_var_screeninfo will result in a
> KASAN: vmalloc-out-of-bounds failure in bitfill_aligned() as
> the margins are being cleared. The margins are cleared in
> chunks and if the xres setting or yres setting is a value of
> zero upto the chunk size, the failure will occur.
> 
> Add a margin check to validate xres and yres settings.
> 
> Signed-off-by: George Kennedy <george.kennedy@oracle.com>
> Suggested-by: Dan Carpenter <dan.carpenter@oracle.com>

Suggested-by is perhaps a bit strong.  Let's change that to:

Reviewed-by: Dan Carpenter <dan.carpenter@oracle.com>

regards,
dan carpenter

Re: [PATCH 1/1] fbmem: add margin check to fb_check_caps()

[Bartlomiej Zolnierkiewicz]

[ added dri-devel ML to Cc: ]

On 7/7/20 9:47 PM, Dan Carpenter wrote:
> On Tue, Jul 07, 2020 at 03:26:03PM -0400, George Kennedy wrote:
>> A fb_ioctl() FBIOPUT_VSCREENINFO call with invalid xres setting
>> or yres setting in struct fb_var_screeninfo will result in a
>> KASAN: vmalloc-out-of-bounds failure in bitfill_aligned() as
>> the margins are being cleared. The margins are cleared in
>> chunks and if the xres setting or yres setting is a value of
>> zero upto the chunk size, the failure will occur.
>>
>> Add a margin check to validate xres and yres settings.
>>
>> Signed-off-by: George Kennedy <george.kennedy@oracle.com>
>> Suggested-by: Dan Carpenter <dan.carpenter@oracle.com>
> 
> Suggested-by is perhaps a bit strong.  Let's change that to:
> 
> Reviewed-by: Dan Carpenter <dan.carpenter@oracle.com>

Applied to drm-misc-next tree, thanks and sorry for the delay.

Best regards,
--
Bartlomiej Zolnierkiewicz
Samsung R&D Institute Poland
Samsung Electronics