On Thu, 22 Feb 2024 14:23:39 -0800 Kees Cook <keescook@xxxxxxxxxxxx> wrote: > Clang tripped over a FORTIFY warning in this code, and while it seems it > may be a false positive in Clang due to loop unwinding, the code in > question seems to make a lot of assumptions. Hi Kees, The assumptions are mostly characteristics of how the IIO buffers work with the scan masks defined based on indexes in the driver provided struct iio_chan_spec arrays. This driver is doing more work than it should need to as we long ago moved some of the more fiddly handling into the IIO core. > Comments added, and the > Clang warning[1] has been worked around by growing the array size. > Also there was an uninitialized 4th byte in the __be32 array that was > being sent through to iio_push_to_buffers(). That is indeed not good - the buffer should have been zero initialized. > > Link: https://github.com/ClangBuiltLinux/linux/issues/2000 [1] > Signed-off-by: Kees Cook <keescook@xxxxxxxxxxxx> > --- > Cc: Jonathan Cameron <jic23@xxxxxxxxxx> > Cc: Lars-Peter Clausen <lars@xxxxxxxxxx> > Cc: "Uwe Kleine-König" <u.kleine-koenig@xxxxxxxxxxxxxx> > Cc: Andy Shevchenko <andriy.shevchenko@xxxxxxxxxxxxxxx> > Cc: "Nuno Sá" <nuno.sa@xxxxxxxxxx> > Cc: linux-iio@xxxxxxxxxxxxxxx > --- > drivers/iio/pressure/dlhl60d.c | 11 +++++++++-- > 1 file changed, 9 insertions(+), 2 deletions(-) > > diff --git a/drivers/iio/pressure/dlhl60d.c b/drivers/iio/pressure/dlhl60d.c > index 28c8269ba65d..9bbecd0bfe88 100644 > --- a/drivers/iio/pressure/dlhl60d.c > +++ b/drivers/iio/pressure/dlhl60d.c > @@ -250,20 +250,27 @@ static irqreturn_t dlh_trigger_handler(int irq, void *private) > struct dlh_state *st = iio_priv(indio_dev); > int ret; > unsigned int chn, i = 0; > - __be32 tmp_buf[2]; > + /* This was only an array pair of 4 bytes. */ True, which is the right size as far as I can tell. If we need this to suppress a warning then comment should say that. > + __be32 tmp_buf[4] = { }; > > ret = dlh_start_capture_and_read(st); > if (ret) > goto out; > > + /* Nothing was checking masklength vs ARRAY_SIZE(tmp_buf)? */ Not needed but no way a compiler could know that. > + if (WARN_ON_ONCE(indio_dev->masklength > ARRAY_SIZE(tmp_buf))) > + goto out; > + > for_each_set_bit(chn, indio_dev->active_scan_mask, This is all a bit pointless if not 'wrong' other than the 4th byte uninitialized part. The limit can be hard coded as 2 as that's a characteristic of this driver. For device that always read a particular set of channels they should provide indio_dev->available_scan_masks = { BIT(1) | BIT(0), 0 }; and then always push all the data making this always memcpy(&tmp_buf[0], &st->rx_buf[1], 3); mempcy(&tmp_buf[1], &st->rx_buf[1] + 3, 3); The buffer demux code in the IIO core will deal with repacking the data if only one channel is enabled. > indio_dev->masklength) { > - memcpy(tmp_buf + i, > + /* This is copying 3 bytes. What about the 4th? */ > + memcpy(&tmp_buf[i], > &st->rx_buf[1] + chn * DLH_NUM_DATA_BYTES, > DLH_NUM_DATA_BYTES); > i++; > } > > + /* How do we know the iio buffer_list has only 2 items? */ Can only include items from the channels array at indexes up to the max scan_index in there, so 0 and 1 in this case (1 might not be present if only one channel is enabled). Sizes (and alignment) are given by storagebits so 4 bytes for each. > iio_push_to_buffers(indio_dev, tmp_buf); > > out:
