iio:light:st_uvis25: Fix timestamp alignment and prevent data leak.

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 suitable structure in the iio_priv()

This data is allocated with kzalloc() so no data can leak apart
from previous readings.

A local unsigned int variable is used for the regmap call so it
is clear there is no potential issue with writing into the padding
of the structure.

Fixes: 3025c8688c1e ("iio: light: add support for UVIS25 sensor")
Reported-by: Lars-Peter Clausen <lars@metafoo.de>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Reviewed-by: Alexandru Ardelean <alexandru.ardelean@analog.com>
Acked-by: Lorenzo Bianconi <lorenzo@kernel.org>
Cc: <Stable@vger.kernel.org>
Link: https://lore.kernel.org/r/20200920112742.170751-3-jic23@kernel.org

diff --git a/drivers/iio/light/st_uvis25.h b/drivers/iio/light/st_uvis25.h
index 78bc56aad1299f3feb659304a1341f3ea4839413..283086887caf5d4f750e7b79f01c8bf91a982aa3 100644 (file)
--- a/drivers/iio/light/st_uvis25.h
+++ b/drivers/iio/light/st_uvis25.h
@@ -27,6 +27,11 @@ struct st_uvis25_hw {
        struct iio_trigger *trig;
        bool enabled;
        int irq;
+       /* Ensure timestamp is naturally aligned */
+       struct {
+               u8 chan;
+               s64 ts __aligned(8);
+       } scan;
 };
 
 extern const struct dev_pm_ops st_uvis25_pm_ops;

diff --git a/drivers/iio/light/st_uvis25_core.c b/drivers/iio/light/st_uvis25_core.c
index a18a82e6bbf5d6f76876b1c9ca2cbe5a64def8bf..1055594b22764e5ec7f7df5d0a80163a0150d300 100644 (file)
--- a/drivers/iio/light/st_uvis25_core.c
+++ b/drivers/iio/light/st_uvis25_core.c
@@ -232,17 +232,19 @@ static const struct iio_buffer_setup_ops st_uvis25_buffer_ops = {
 
 static irqreturn_t st_uvis25_buffer_handler_thread(int irq, void *p)
 {
-       u8 buffer[ALIGN(sizeof(u8), sizeof(s64)) + sizeof(s64)];
        struct iio_poll_func *pf = p;
        struct iio_dev *iio_dev = pf->indio_dev;
        struct st_uvis25_hw *hw = iio_priv(iio_dev);
+       unsigned int val;
        int err;
 
-       err = regmap_read(hw->regmap, ST_UVIS25_REG_OUT_ADDR, (int *)buffer);
+       err = regmap_read(hw->regmap, ST_UVIS25_REG_OUT_ADDR, &val);
        if (err < 0)
                goto out;
 
-       iio_push_to_buffers_with_timestamp(iio_dev, buffer,
+       hw->scan.chan = val;
+
+       iio_push_to_buffers_with_timestamp(iio_dev, &hw->scan,
                                           iio_get_time_ns(iio_dev));
 
 out: