Google Android Broadcom Wi-fi Driver Information Disclosure Vulnerability(CVE-2017-0633)

2017-05-27T00:00:00
ID SSV:93160
Type seebug
Reporter Root
Modified 2017-05-27T00:00:00

Description

An information disclosure vulnerability in the Broadcom Wi-Fi driver could enable a local malicious component to access data outside of its permission levels. This issue is rated as Moderate because it first requires compromising a privileged process. Product: Android. Versions: Kernel-3.10, Kernel-3.18. Android ID: A-36000515. References: B-RB#117131.

Broadcom produces Wi-Fi HardMAC SoCs which are used to handle the PHY and MAC layer processing. These chips are present in both mobile devices and Wi-Fi routers, and are capable of handling many Wi-Fi related events without delegating to the host OS. On Android devices, the "bcmdhd" driver is used in order to communicate with the Wi-Fi SoC (also referred to as "dongle").

Along with the regular flow of frames transferred between the host and the dongle, the two communicate with one another via a set of "ioctls" which can be issued to read or write dongle configuration from the host. This information is exchanged using the SDIO "control" channel (SDPCM_CONTROL_CHANNEL) rather than the regular "data" and "glom" channels (which are used to transfer frames).

When the "bcmdhd" driver wishes to send a ioctl to the dongle, it does so by calling "wldev_ioctl". This function has the following signature:

s32 wldev_ioctl(struct net_device dev, u32 cmd, void arg, u32 len, u32 set)

Where "arg" is a pointer to the argument supplied to the ioctl call, and "len" indicates the length of this argument. This function transfers the supplied buffer over SDIO to the dongle, where it is handled by the dongle's ioctl handler function.

The "bcmdhd" driver issues many such ioctls, either when accessing iovars, or when reading and writing configuration used by the dongle. However, in all of these cases, "bcmdhd" neglects to clear the unused memory in the supplied argument buffer before calling "wldev_ioctl". As a result, the buffers transferred via the ioctl calls contain uninitialised memory, including pointers and other information processed by the driver.

To demonstrate this issue, I've located the needed symbols on the Nexus 6P (NUF26K, BCM4358 version 7.112.201.1). The dongle's ioctl handler is at located at ROM address 0x19734, and the pointer to the registered ioctl handler is located in RAM address 0x214BF0. By patching the RAM address to point to a newly allocated code stub, we are able to intercept the ioctl handler on the dongle.

I've written a small code stub which instruments the ioctl handler in order to dump the contents of the buffers passed in by the host. Here's a small sample of these log dumps: (1237) ioctl - code: 262, length: 512 (1238) 0 : 6f737361 (1239) 4 : 65725f63 (1240) 8 : 65695f71 ... (1404) 148 : ffffffc0 (1405) 152 : 00cdd204 (1406) 156 : ffffffc0 (1407) 160 : 5bd4b6f0 (1408) 164 : ffffffc0 (1409) 168 : 003ee868 (1410) 172 : ffffffc0 (1411) 176 : 5bd4b7e0 (1412) 180 : ffffffc0 (1413) 184 : 5bd4b810 (1414) 188 : ffffffc0 (1415) 192 : 5bd4b790 (1416) 196 : ffffffc0 As can be seen in the log above, the buffer contains multiple pointers from the host's kernel. This issue can be addressed by clearing the unused memory in the passed in argument buffers prior to calling "wldev_ioctl".