From: Tetsuo Handa <penguin-kernel@i-love.sakura.ne.jp>
Date: Mon, 31 Aug 2020 10:37:00 +0000 (+0900)
Subject: video: fbdev: fix OOB read in vga_8planes_imageblit()
X-Git-Tag: v4.4.237~23
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=80bca1ca2f1c6cb2f48c2bf3060567337d197f56;p=thirdparty%2Fkernel%2Fstable.git

video: fbdev: fix OOB read in vga_8planes_imageblit()

commit bd018a6a75cebb511bb55a0e7690024be975fe93 upstream.

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>
---

diff --git a/drivers/video/fbdev/vga16fb.c b/drivers/video/fbdev/vga16fb.c
index 283d335a759fe..1acdb41a8a7c3 100644
--- a/drivers/video/fbdev/vga16fb.c
+++ b/drivers/video/fbdev/vga16fb.c
@@ -1122,7 +1122,7 @@ 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;