From bd018a6a75cebb511bb55a0e7690024be975fe93 Mon Sep 17 00:00:00 2001
From: Tetsuo Handa <penguin-kernel@i-love.sakura.ne.jp>
Date: Mon, 31 Aug 2020 19:37:00 +0900
Subject: [PATCH] video: fbdev: fix OOB read in vga_8planes_imageblit()
Git-commit: bd018a6a75cebb511bb55a0e7690024be975fe93
Patch-mainline: v5.9-rc5
References: git-fixes

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@syzkaller.appspotmail.com>
Signed-off-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Cc: stable <stable@vger.kernel.org>
Link: https://lore.kernel.org/r/90b55ec3-d5b0-3307-9f7c-7ff5c5fd6ad3@i-love.sakura.ne.jp
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Acked-by: Takashi Iwai <tiwai@suse.de>

---
 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;
-- 
2.16.4