From a03ff54460817c76105f81f3aa8ef655759ccc9a Mon Sep 17 00:00:00 2001
From: Alan Stern <stern@rowland.harvard.edu>
Date: Mon, 13 May 2019 13:14:29 -0400
Subject: [PATCH] USB: Fix slab-out-of-bounds write in usb_get_bos_descriptor
Git-commit: a03ff54460817c76105f81f3aa8ef655759ccc9a
Patch-mainline: v5.2-rc3
References: bsc#1051510

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>
Acked-by: Takashi Iwai <tiwai@suse.de>

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

diff --git a/drivers/usb/core/config.c b/drivers/usb/core/config.c
index 20ff036b4c22..9d6cb709ca7b 100644
--- a/drivers/usb/core/config.c
+++ b/drivers/usb/core/config.c
@@ -932,8 +932,8 @@ int usb_get_bos_descriptor(struct usb_device *dev)
 
 	/* 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);
-- 
2.16.4