iio: gyro: itg3200: fix i2c read into the wrong stack location

itg3200_read_all_channels() takes `__be16 *buf' as a parameter and
fills the i2c_msg destination as `(char *)&buf'. Since `buf' is the
parameter (a pointer), `&buf' is the address of the local pointer
slot on the stack of itg3200_read_all_channels(), not the address
of the caller's scan buffer. The (char *) cast hides the type
mismatch.

i2c_transfer() therefore writes ITG3200_SCAN_ELEMENTS * sizeof(s16)
= 8 bytes into the parameter's stack slot, which is discarded when
the function returns. The caller's scan buffer in
itg3200_trigger_handler() is never written to, so
iio_push_to_buffers_with_timestamp() pushes uninitialised stack
contents to userspace via /dev/iio:deviceX every scan -- both a
functional bug (no actual gyroscope or temperature data is
delivered through the triggered buffer) and an information leak.

The non-buffered read_raw() path is unaffected: it goes through
itg3200_read_reg_s16() which uses `&out' on a local s16 value,
where that is correct.

Drop the spurious `&' so the i2c read writes into the caller's
buffer.

Fixes: 9dbf091da0 ("iio: gyro: Add itg3200")
Cc: stable@vger.kernel.org
Signed-off-by: David Carlier <devnexen@gmail.com>
Reviewed-by: Andy Shevchenko <andriy.shevchenko@intel.com>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>

drivers/iio/gyro/itg3200_buffer.c

@@ -34,7 +34,7 @@ static int itg3200_read_all_channels(struct i2c_client *i2c, __be16 *buf)
 			.addr = i2c->addr,
 			.flags = i2c->flags | I2C_M_RD,
 			.len = ITG3200_SCAN_ELEMENTS * sizeof(s16),
-			.buf = (char *)&buf,
+			.buf = (char *)buf,
 		},
 	};