Affected: Linux

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 l…