linux-kernel - [PATCH 3.16.y-ckt 11/17] USB: cdc-acm: more sanity checking

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Date:	Tue, 12 Apr 2016 19:07:58 +0100
From:	Luis Henriques <luis.henriques@...onical.com>
To:	linux-kernel@...r.kernel.org, stable@...r.kernel.org,
	kernel-team@...ts.ubuntu.com
Cc:	Oliver Neukum <ONeukum@...e.com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Moritz Muehlenhoff <jmm@...til.org>,
	Luis Henriques <luis.henriques@...onical.com>
Subject: [PATCH 3.16.y-ckt 11/17] USB: cdc-acm: more sanity checking

3.16.7-ckt27 -stable review patch.  If anyone has any objections, please let me know.

---8<------------------------------------------------------------

From: Oliver Neukum <oneukum@...e.com>

commit 8835ba4a39cf53f705417b3b3a94eb067673f2c9 upstream.

An attack has become available which pretends to be a quirky
device circumventing normal sanity checks and crashes the kernel
by an insufficient number of interfaces. This patch adds a check
to the code path for quirky devices.

Signed-off-by: Oliver Neukum <ONeukum@...e.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc: Moritz Muehlenhoff <jmm@...til.org>
Signed-off-by: Luis Henriques <luis.henriques@...onical.com>
---
 drivers/usb/class/cdc-acm.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/drivers/usb/class/cdc-acm.c b/drivers/usb/class/cdc-acm.c
index 332be4c5745c..54061a3bc5e9 100644
--- a/drivers/usb/class/cdc-acm.c
+++ b/drivers/usb/class/cdc-acm.c
@@ -1104,6 +1104,9 @@ static int acm_probe(struct usb_interface *intf,
 	if (quirks == NO_UNION_NORMAL) {
 		data_interface = usb_ifnum_to_if(usb_dev, 1);
 		control_interface = usb_ifnum_to_if(usb_dev, 0);
+		/* we would crash */
+		if (!data_interface || !control_interface)
+			return -ENODEV;
 		goto skip_normal_probe;
 	}