From:   Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To:     linux-kernel@vger.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        stable@vger.kernel.org, Pekka Korpinen <pekka.korpinen@iki.fi>,
        Stable@vger.kernel.org,
        Jonathan Cameron <Jonathan.Cameron@huawei.com>
Subject: [PATCH 4.9 053/207] iio: dac: ad5446: Fix ad5622_write() return value
Date:   Wed, 24 Nov 2021 12:55:24 +0100
Message-Id: <20211124115705.640977206@linuxfoundation.org>
In-Reply-To: <20211124115703.941380739@linuxfoundation.org>
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From: Pekka Korpinen <pekka.korpinen@iki.fi>

commit 558df982d4ead9cac628153d0d7b60feae05ddc8 upstream.

On success i2c_master_send() returns the number of bytes written. The
call from iio_write_channel_info(), however, expects the return value to
be zero on success.

This bug causes incorrect consumption of the sysfs buffer in
iio_write_channel_info(). When writing more than two characters to
out_voltage0_raw, the ad5446 write handler is called multiple times
causing unexpected behavior.

Fixes: 3ec36a2cf0d5 ("iio:ad5446: Add support for I2C based DACs")
Signed-off-by: Pekka Korpinen <pekka.korpinen@iki.fi>
Link: https://lore.kernel.org/r/20210929185755.2384-1-pekka.korpinen@iki.fi
Cc: <Stable@vger.kernel.org>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 drivers/iio/dac/ad5446.c |    9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

--- a/drivers/iio/dac/ad5446.c
+++ b/drivers/iio/dac/ad5446.c
@@ -510,8 +510,15 @@ static int ad5622_write(struct ad5446_st
 {
 	struct i2c_client *client = to_i2c_client(st->dev);
 	__be16 data = cpu_to_be16(val);
+	int ret;
 
-	return i2c_master_send(client, (char *)&data, sizeof(data));
+	ret = i2c_master_send(client, (char *)&data, sizeof(data));
+	if (ret < 0)
+		return ret;
+	if (ret != sizeof(data))
+		return -EIO;
+
+	return 0;
 }
 
 /**