[PATCH v2 1/2] iio: proximity: sx9310: reject out-of-range hardware gain values

[Arnav Kapoor <kapoorarnav43@gmail.com>]

sx9310_write_gain() passes the value from userspace to ilog2() and then
FIELD_PREP() into a 2-bit gain field without checking it, so some
values silently program a gain unrelated to the one requested, and the
write still reports success:

  - 16 and larger wrap around in the 2-bit field, e.g. 16 sets a gain
    of 1 and 32 a gain of 2;
  - 0 and negative values set the maximum gain of 8, because ilog2(0)
    is -1 and a negative int becomes a large unsigned value.

Return -EINVAL for values <= 0 and for values whose ilog2() does not
fit in the gain field. Values between the supported gains of 1, 2, 4
and 8 are still rounded down, as before, and the gain read back
reflects what was applied.

Fixes: 227c83faa2f8 ("iio: sx9310: Support hardware gain factor")
Signed-off-by: Arnav Kapoor <kapoorarnav43@gmail.com>
---
 drivers/iio/proximity/sx9310.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/drivers/iio/proximity/sx9310.c b/drivers/iio/proximity/sx9310.c
index 2585b9c6fb69..9177d6d4a0a1 100644
--- a/drivers/iio/proximity/sx9310.c
+++ b/drivers/iio/proximity/sx9310.c
@@ -665,16 +665,23 @@ static int sx9310_write_gain(struct sx_common_data *data,
 {
 	unsigned int gain, mask;
 
+	if (val <= 0)
+		return -EINVAL;
+
 	gain = ilog2(val);
 
 	switch (chan->channel) {
 	case 0:
 	case 3:
+		if (!FIELD_FIT(SX9310_REG_PROX_CTRL3_GAIN0_MASK, gain))
+			return -EINVAL;
 		mask = SX9310_REG_PROX_CTRL3_GAIN0_MASK;
 		gain = FIELD_PREP(SX9310_REG_PROX_CTRL3_GAIN0_MASK, gain);
 		break;
 	case 1:
 	case 2:
+		if (!FIELD_FIT(SX9310_REG_PROX_CTRL3_GAIN12_MASK, gain))
+			return -EINVAL;
 		mask = SX9310_REG_PROX_CTRL3_GAIN12_MASK;
 		gain = FIELD_PREP(SX9310_REG_PROX_CTRL3_GAIN12_MASK, gain);
 		break;
-- 
2.53.0