linux-kernel - [PATCH] fbdev: controlfb: Add missing modes to fix out of bounds access

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Date:   Tue,  7 Nov 2017 15:05:05 +0100
From:   Geert Uytterhoeven <geert@...ux-m68k.org>
To:     Bartlomiej Zolnierkiewicz <b.zolnierkie@...sung.com>
Cc:     Dan Carpenter <dan.carpenter@...cle.com>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        linux-fbdev@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org,
        linux-kernel@...r.kernel.org,
        Geert Uytterhoeven <geert@...ux-m68k.org>
Subject: [PATCH] fbdev: controlfb: Add missing modes to fix out of bounds access

Dan's static analysis says:

    drivers/video/fbdev/controlfb.c:560 control_setup()
    error: buffer overflow 'control_mac_modes' 20 <= 21

Indeed, control_mac_modes[] has only 20 elements, while VMODE_MAX is 22,
which may lead to an out of bounds read when parsing vmode commandline
options.

The bug was introduced in v2.4.5.6, when 2 new modes were added to
macmodes.h, but control_mac_modes[] wasn't updated:

https://kernel.opensuse.org/cgit/kernel/diff/include/video/macmodes.h?h=v2.5.2&id=29f279c764808560eaceb88fef36cbc35c529aad

Augment control_mac_modes[] with the two new video modes to fix this.

Reported-by: Dan Carpenter <dan.carpenter@...cle.com>
Signed-off-by: Geert Uytterhoeven <geert@...ux-m68k.org>
---
Compile-tested only.

The 1152x768 mode should be OK.
Given the 1600x1024 mode has a lower dotclock (112 MHz) than the
supported 1280x960 mode, it's probably OK, too.
---
 drivers/video/fbdev/controlfb.h | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/drivers/video/fbdev/controlfb.h b/drivers/video/fbdev/controlfb.h
index 6026c60fc1007e00..261522fabdac89ae 100644
--- a/drivers/video/fbdev/controlfb.h
+++ b/drivers/video/fbdev/controlfb.h
@@ -141,5 +141,7 @@ static struct max_cmodes control_mac_modes[] = {
 	{{ 1, 2}},	/* 1152x870, 75Hz */
 	{{ 0, 1}},	/* 1280x960, 75Hz */
 	{{ 0, 1}},	/* 1280x1024, 75Hz */
+	{{ 1, 2}},	/* 1152x768, 60Hz */
+	{{ 0, 1}},	/* 1600x1024, 60Hz */
 };
 
-- 
2.7.4