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From:   Phong Tran <tranmanphong@gmail.com>
To:     syzbot+495dab1f175edc9c2f13@syzkaller.appspotmail.com
Cc:     2pi@mok.nu, alex.theissen@me.com, andreyknvl@google.com,
        gregkh@linuxfoundation.org, linux-kernel@vger.kernel.org,
        linux-usb@vger.kernel.org, syzkaller-bugs@googlegroups.com,
        linux-kernel-mentees@lists.linuxfoundation.org,
        Phong Tran <tranmanphong@gmail.com>
Subject: [PATCH] usb: appledisplay: fix use-after-free in bl_get_brightness
Date:   Wed,  6 Nov 2019 06:36:52 +0700
Message-Id: <20191105233652.21033-1-tranmanphong@gmail.com>
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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@syzkaller.appspotmail.com
Reported-and-tested-by:
syzbot+495dab1f175edc9c2f13@syzkaller.appspotmail.com

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

Signed-off-by: Phong Tran <tranmanphong@gmail.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