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.

Fixes: 3bbec9773389 ("iio: bmc150_accel: add support for hardware fifo")
Cc: stable@vger.kernel.org
Signed-off-by: Bryam Vargas <hexlabsecurity@proton.me>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>

diff --git a/drivers/iio/accel/bmc150-accel-core.c b/drivers/iio/accel/bmc150-accel-core.c
index 2398eb7e12cdd25ce0ac988a9535c7a833eb664a..dc8a6285cf3df462de43fbcab11c19942dc2f7f3 100644 (file)
--- a/drivers/iio/accel/bmc150-accel-core.c
+++ b/drivers/iio/accel/bmc150-accel-core.c
@@ -991,6 +991,8 @@ static int __bmc150_accel_fifo_flush(struct iio_dev *indio_dev,
        if (samples && count > samples)
                count = samples;
 
+       count = min_t(u8, count, BMC150_ACCEL_FIFO_LENGTH);
+
        ret = bmc150_accel_fifo_transfer(data, (u8 *)buffer, count);
        if (ret)
                return ret;