linux-kernel - [PATCH 5.8 164/177] video: fbdev: fix OOB read in vga_8planes

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Date:   Tue, 15 Sep 2020 16:13:55 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org,
        syzbot <syzbot+69fbd3e01470f169c8c4@...kaller.appspotmail.com>,
        Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
Subject: [PATCH 5.8 164/177] video: fbdev: fix OOB read in vga_8planes_imageblit()

From: Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>

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@...kaller.appspotmail.com>
Signed-off-by: Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
Cc: stable <stable@...r.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@...uxfoundation.org>

---
 drivers/video/fbdev/vga16fb.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/drivers/video/fbdev/vga16fb.c
+++ b/drivers/video/fbdev/vga16fb.c
@@ -1121,7 +1121,7 @@ static void vga_8planes_imageblit(struct
         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;