linux-kernel - [PATCH] usb: appledisplay: fix use-after-free in bl_get

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Date:   Wed,  6 Nov 2019 06:36:52 +0700
From:   Phong Tran <tranmanphong@...il.com>
To:     syzbot+495dab1f175edc9c2f13@...kaller.appspotmail.com
Cc:     2pi@....nu, alex.theissen@...com, andreyknvl@...gle.com,
        gregkh@...uxfoundation.org, linux-kernel@...r.kernel.org,
        linux-usb@...r.kernel.org, syzkaller-bugs@...glegroups.com,
        linux-kernel-mentees@...ts.linuxfoundation.org,
        Phong Tran <tranmanphong@...il.com>
Subject: [PATCH] usb: appledisplay: fix use-after-free in bl_get_brightness

In context of USB disconnect, the delaywork trigger and calling
appledisplay_bl_get_brightness() and the msgdata was freed.

add the checking return value of usb_control_msg() and only update the
data while the retval is valid.

Reported-by: syzbot+495dab1f175edc9c2f13@...kaller.appspotmail.com
Reported-and-tested-by:
syzbot+495dab1f175edc9c2f13@...kaller.appspotmail.com

https://groups.google.com/d/msg/syzkaller-bugs/dRmkh2UYusY/l2a6Mg3FAQAJ

Signed-off-by: Phong Tran <tranmanphong@...il.com>
---
 drivers/usb/misc/appledisplay.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/usb/misc/appledisplay.c b/drivers/usb/misc/appledisplay.c
index ac92725458b5..3e3dfa5a3954 100644
--- a/drivers/usb/misc/appledisplay.c
+++ b/drivers/usb/misc/appledisplay.c
@@ -164,7 +164,8 @@ static int appledisplay_bl_get_brightness(struct backlight_device *bd)
 		0,
 		pdata->msgdata, 2,
 		ACD_USB_TIMEOUT);
-	brightness = pdata->msgdata[1];
+	if (retval >= 0)
+		brightness = pdata->msgdata[1];
 	mutex_unlock(&pdata->sysfslock);
 
 	if (retval < 0)
-- 
2.20.1