iio: accel: bmc150: clamp the device-reported FIFO frame count

Overview

In the Linux kernel, the following vulnerability has been resolved:

iio: accel: bmc150: clamp the device-reported FIFO frame count

__bmc150_accel_fifo_flush() copies the number of samples the device reports in its hardware FIFO into an on-stack buffer

u16 buffer[BMC150_ACCEL_FIFO_LENGTH * 3];

which is sized for at most BMC150_ACCEL_FIFO_LENGTH (32) samples. The frame count is read from the FIFO_STATUS register and only masked to its 7 valid bits:

count = val & 0x7F;

so it can be 0..127. The only other limit applied to it is the optional caller-supplied sample budget:

if (samples && count > samples)
	count = samples;

which does not constrain count on the flush-all path (samples == 0), and leaves it well above 32 whenever samples is larger. count samples are then transferred into buffer[]:

bmc150_accel_fifo_transfer(data, (u8 *)buffer, count);

bmc150_accel_fifo_transfer() reads count * 6 bytes through regmap, so a malfunctioning, malicious or counterfeit accelerometer (or an attacker tampering with the I2C/SPI bus) that reports up to 127 frames writes up to 762 bytes into the 192-byte buffer: a stack out-of-bounds write of up to 570 bytes that clobbers the stack canary, saved registers and the return address.

Clamp count to BMC150_ACCEL_FIFO_LENGTH, the number of samples buffer[] is sized for, before the transfer, mirroring the watermark clamp already done in bmc150_accel_set_watermark(). A well-formed flush reports at most BMC150_ACCEL_FIFO_LENGTH frames, so legitimate devices are unaffected.

Affected

• Linux >= 3bbec9773389112330954a6a64422eaa78d546c1 < b5a9f521e0a49a0266200fd535b32a9668ecb33b
• Linux >= 3bbec9773389112330954a6a64422eaa78d546c1 < 2fe0531dd73eff1de0f2584cb77716d645e548d5
• Linux >= 3bbec9773389112330954a6a64422eaa78d546c1 < d0e6d924a5484e005cae5aff6a0aa07a22f3c9ff
• Linux >= 3bbec9773389112330954a6a64422eaa78d546c1 < bfffc98f3de92e0f76be7c7b72e63ac1776a6dbc
• Linux >= 3bbec9773389112330954a6a64422eaa78d546c1 < 89f4a4ca0ac3a933c750569a771c079a290b0721
• Linux >= 3bbec9773389112330954a6a64422eaa78d546c1 < 3e766526827acd542bcd36c20c4d5f397e0f6521
• Linux >= 3bbec9773389112330954a6a64422eaa78d546c1 < 35a3cd8fd65e15029eb90f1e510045b1bb071175
• Linux >= 3bbec9773389112330954a6a64422eaa78d546c1 < ce0e1cae26096fe959a0da5563a6d6d5a801d5fb
• Linux 4.1

Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.