[PATCH] iio: dac: mcp47feb02: reject out-of-range raw values

[David Carlier <devnexen@gmail.com>]

mcp47feb02_write_raw() writes the user supplied raw value to the DAC
register without checking it against the chip resolution. The parts
are 8, 10 or 12 bit, and the bits above the resolution are not
implemented, so writing 300 to out_voltage0_raw on an 8-bit part sets
the output to code 44 instead of failing, and -1 is written as 0xffff.

The out-of-range value is also cached in dac_data, so it is written
back on resume and stored to EEPROM by store_eeprom.

Return -EINVAL for values outside [0, 2^resolution - 1].

Found by code inspection. Build tested with W=1 (=m and =y) only;
no hardware was available for runtime testing.

Fixes: bf394cc80369 ("iio: dac: adding support for Microchip MCP47FEB02")
Cc: stable@vger.kernel.org
Assisted-by: LLM
Signed-off-by: David Carlier <devnexen@gmail.com>
---
 drivers/iio/dac/mcp47feb02-core.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/drivers/iio/dac/mcp47feb02-core.c b/drivers/iio/dac/mcp47feb02-core.c
index 88bffbab0854..1a0e80b5db87 100644
--- a/drivers/iio/dac/mcp47feb02-core.c
+++ b/drivers/iio/dac/mcp47feb02-core.c
@@ -696,6 +696,9 @@ static int mcp47feb02_write_raw(struct iio_dev *indio_dev, struct iio_chan_spec
 
 	switch (mask) {
 	case IIO_CHAN_INFO_RAW:
+		if (val < 0 || val >= BIT(data->chip_features->resolution))
+			return -EINVAL;
+
 		ret = regmap_write(data->regmap, REG_ADDR(ch->address), val);
 		if (ret)
 			return ret;
-- 
2.55.0