Re: [PATCH 12/25] iio:imu:st_lsm6dsx Fix alignment and data leak issues

[Jonathan Cameron <jic23@kernel.org>]

On Tue, 26 May 2020 09:58:38 +0200
Lorenzo Bianconi <lorenzo@kernel.org> wrote:

> > From: Jonathan Cameron <Jonathan.Cameron@huawei.com>
> > 
> > One of a class of bugs pointed out by Lars in a recent review.
> > iio_push_to_buffers_with_timestamp assumes the buffer used is aligned
> > to the size of the timestamp (8 bytes).  This is not guaranteed in
> > this driver which uses an array of smaller elements on the stack.
> > As Lars also noted this anti pattern can involve a leak of data to
> > userspace and that indeed can happen here.  We close both issues by
> > moving to a set of suitable structures in the iio_priv() data.
> > 
> > This data is allocated with kzalloc so no data can leak apart from
> > previous readings.
> > 
> > There has been a lot of churn in this driver, so likely backports
> > may be needed for stable.
> > 
> > Fixes: 290a6ce11d93 ("iio: imu: add support to lsm6dsx driver")
> > Reported-by: Lars-Peter Clausen <lars@metafoo.de>
> > Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
> > Cc: Lorenzo Bianconi <lorenzo.bianconi83@gmail.com>
> > ---
> >  drivers/iio/imu/st_lsm6dsx/st_lsm6dsx.h       |  5 ++++
> >  .../iio/imu/st_lsm6dsx/st_lsm6dsx_buffer.c    | 27 ++++++++++---------
> >  2 files changed, 20 insertions(+), 12 deletions(-)
> > 
> > diff --git a/drivers/iio/imu/st_lsm6dsx/st_lsm6dsx.h b/drivers/iio/imu/st_lsm6dsx/st_lsm6dsx.h
> > index b56df409ed0f..5bc724eadc83 100644
> > --- a/drivers/iio/imu/st_lsm6dsx/st_lsm6dsx.h
> > +++ b/drivers/iio/imu/st_lsm6dsx/st_lsm6dsx.h
> > @@ -411,6 +411,11 @@ struct st_lsm6dsx_hw {
> >  	const struct st_lsm6dsx_settings *settings;
> >  
> >  	struct iio_mount_matrix orientation;
> > +	/* Ensure natural alignment of buffer elements */
> > +	struct {
> > +		__le16 channels[3];
> > +		s64 ts;
> > +	} gyro_scan, acc_scan, ext_scan;
> >  };
> >  
> >  static __maybe_unused const struct iio_event_spec st_lsm6dsx_event = {
> > diff --git a/drivers/iio/imu/st_lsm6dsx/st_lsm6dsx_buffer.c b/drivers/iio/imu/st_lsm6dsx/st_lsm6dsx_buffer.c
> > index afd00daeefb2..9bcffbfac797 100644
> > --- a/drivers/iio/imu/st_lsm6dsx/st_lsm6dsx_buffer.c
> > +++ b/drivers/iio/imu/st_lsm6dsx/st_lsm6dsx_buffer.c
> > @@ -341,9 +341,6 @@ int st_lsm6dsx_read_fifo(struct st_lsm6dsx_hw *hw)
> >  	int err, sip, acc_sip, gyro_sip, ts_sip, ext_sip, read_len, offset;
> >  	u16 fifo_len, pattern_len = hw->sip * ST_LSM6DSX_SAMPLE_SIZE;
> >  	u16 fifo_diff_mask = hw->settings->fifo_ops.fifo_diff.mask;
> > -	u8 gyro_buff[ST_LSM6DSX_IIO_BUFF_SIZE];
> > -	u8 acc_buff[ST_LSM6DSX_IIO_BUFF_SIZE];
> > -	u8 ext_buff[ST_LSM6DSX_IIO_BUFF_SIZE];
> >  	bool reset_ts = false;
> >  	__le16 fifo_status;
> >  	s64 ts = 0;
> > @@ -404,18 +401,21 @@ int st_lsm6dsx_read_fifo(struct st_lsm6dsx_hw *hw)
> >  
> >  		while (acc_sip > 0 || gyro_sip > 0 || ext_sip > 0) {
> >  			if (gyro_sip > 0 && !(sip % gyro_sensor->decimator)) {
> > -				memcpy(gyro_buff, &hw->buff[offset],
> > -				       ST_LSM6DSX_SAMPLE_SIZE);
> > +				memcpy(hw->gyro_scan.channels,
> > +				       &hw->buff[offset],
> > +				       sizeof(hw->gyro_scan.channels));
> >  				offset += ST_LSM6DSX_SAMPLE_SIZE;  
> 
> what about doing?
> 
> offset += sizeof(hw->gyro_scan.channels)
> 
> it seems easier to follow, what do you think?
> 
> >  			}
> >  			if (acc_sip > 0 && !(sip % acc_sensor->decimator)) {
> > -				memcpy(acc_buff, &hw->buff[offset],
> > -				       ST_LSM6DSX_SAMPLE_SIZE);
> > +				memcpy(hw->acc_scan.channels,
> > +				       &hw->buff[offset],
> > +				       sizeof(hw->acc_scan.channels));
> >  				offset += ST_LSM6DSX_SAMPLE_SIZE;  
> 
> same here
> 
> >  			}
> >  			if (ext_sip > 0 && !(sip % ext_sensor->decimator)) {
> > -				memcpy(ext_buff, &hw->buff[offset],
> > -				       ST_LSM6DSX_SAMPLE_SIZE);
> > +				memcpy(hw->ext_scan.channels,
> > +				       &hw->buff[offset],
> > +				       sizeof(hw->ext_scan.channels));
> >  				offset += ST_LSM6DSX_SAMPLE_SIZE;  
> 
> same here

Agreed.  I also missed the tagged path needs alignment.  For that one I did it
directly on the stack.  Please take a look at v2 and let me know if it looks
right to you.

Thanks,

Jonathan

> 
> Regards,
> Lorenzo
> 
> >  			}
> >  
> > @@ -446,19 +446,22 @@ int st_lsm6dsx_read_fifo(struct st_lsm6dsx_hw *hw)
> >  			if (gyro_sip > 0 && !(sip % gyro_sensor->decimator)) {
> >  				iio_push_to_buffers_with_timestamp(
> >  					hw->iio_devs[ST_LSM6DSX_ID_GYRO],
> > -					gyro_buff, gyro_sensor->ts_ref + ts);
> > +					&hw->gyro_scan,
> > +					gyro_sensor->ts_ref + ts);
> >  				gyro_sip--;
> >  			}
> >  			if (acc_sip > 0 && !(sip % acc_sensor->decimator)) {
> >  				iio_push_to_buffers_with_timestamp(
> >  					hw->iio_devs[ST_LSM6DSX_ID_ACC],
> > -					acc_buff, acc_sensor->ts_ref + ts);
> > +					&hw->acc_scan,
> > +					acc_sensor->ts_ref + ts);
> >  				acc_sip--;
> >  			}
> >  			if (ext_sip > 0 && !(sip % ext_sensor->decimator)) {
> >  				iio_push_to_buffers_with_timestamp(
> >  					hw->iio_devs[ST_LSM6DSX_ID_EXT0],
> > -					ext_buff, ext_sensor->ts_ref + ts);
> > +					&hw->ext_scan,
> > +					ext_sensor->ts_ref + ts);
> >  				ext_sip--;
> >  			}
> >  			sip++;
> > -- 
> > 2.26.2
> >