[PATCH 4.14 52/94] video: fbdev: fix OOB read in vga_8planes_imageblit()

Greg Kroah-Hartman
2020-09-21T17:02:00Z

From: Tetsuo Handa <penguin-kernel@i-love.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@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>

---
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
@@ -1122,7 +1122,7 @@ 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;