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From:   Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To:     linux-kernel@vger.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        stable@vger.kernel.org, Alan Stern <stern@rowland.harvard.edu>,
        syzbot+71f1e64501a309fcc012@syzkaller.appspotmail.com
Subject: [PATCH 4.14 29/69] USB: Fix slab-out-of-bounds write in usb_get_bos_descriptor
Date:   Fri,  7 Jun 2019 17:39:10 +0200
Message-Id: <20190607153851.981453928@linuxfoundation.org>
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From: Alan Stern <stern@rowland.harvard.edu>

commit a03ff54460817c76105f81f3aa8ef655759ccc9a upstream.

The syzkaller USB fuzzer found a slab-out-of-bounds write bug in the
USB core, caused by a failure to check the actual size of a BOS
descriptor.  This patch adds a check to make sure the descriptor is at
least as large as it is supposed to be, so that the code doesn't
inadvertently access memory beyond the end of the allocated region
when assigning to dev->bos->desc->bNumDeviceCaps later on.

Signed-off-by: Alan Stern <stern@rowland.harvard.edu>
Reported-and-tested-by: syzbot+71f1e64501a309fcc012@syzkaller.appspotmail.com
CC: <stable@vger.kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
 drivers/usb/core/config.c |    4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

--- a/drivers/usb/core/config.c
+++ b/drivers/usb/core/config.c
@@ -936,8 +936,8 @@ int usb_get_bos_descriptor(struct usb_de
 
 	/* Get BOS descriptor */
 	ret = usb_get_descriptor(dev, USB_DT_BOS, 0, bos, USB_DT_BOS_SIZE);
-	if (ret < USB_DT_BOS_SIZE) {
-		dev_err(ddev, "unable to get BOS descriptor\n");
+	if (ret < USB_DT_BOS_SIZE || bos->bLength < USB_DT_BOS_SIZE) {
+		dev_err(ddev, "unable to get BOS descriptor or descriptor too short\n");
 		if (ret >= 0)
 			ret = -ENOMSG;
 		kfree(bos);