[PATCH 4.19 30/33] fbmem: add margin check to fb_check_caps()

From: George Kennedy <redacted>

commit a49145acfb975d921464b84fe00279f99827d816 upstream.

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 <redacted>
Reported-by: syzbot+e5fd3e65515b48c02a30@syzkaller.appspotmail.com
Reviewed-by: Dan Carpenter <redacted>
Cc: Dhaval Giani <redacted>
Signed-off-by: Bartlomiej Zolnierkiewicz <redacted>
Link: https://patchwork.freedesktop.org/patch/msgid/1594149963-13801-1-git-send-email-george.kennedy@oracle.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 drivers/video/fbdev/core/fbmem.c |    4 ++++
 1 file changed, 4 insertions(+)

--- a/drivers/video/fbdev/core/fbmem.c
+++ b/drivers/video/fbdev/core/fbmem.c

@@ -991,6 +991,10 @@ fb_set_var(struct fb_info *info, struct
 			goto done;
 		}
 
+		/* 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)