linux-kernel - [10/55] hwmon: (max1111) Fix race condition causing NULL pointer exception

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Message-Id: <20110806000249.880122195@clark.kroah.org>
Date:	Fri, 05 Aug 2011 17:01:40 -0700
From:	Greg KH <gregkh@...e.de>
To:	linux-kernel@...r.kernel.org, stable@...nel.org
Cc:	stable-review@...nel.org, torvalds@...ux-foundation.org,
	akpm@...ux-foundation.org, alan@...rguk.ukuu.org.uk,
	Pavel Herrmann <morpheus.ibis@...il.com>,
	Russell King <rmk+kernel@....linux.org.uk>,
	Pavel Machek <pavel@....cz>,
	Marek Vasut <marek.vasut@...il.com>,
	Cyril Hrubis <metan@....cz>, Jean Delvare <khali@...ux-fr.org>
Subject: [10/55] hwmon: (max1111) Fix race condition causing NULL pointer exception

2.6.32-longterm review patch.  If anyone has any objections, please let us know.

------------------

From: Pavel Herrmann <morpheus.ibis@...il.com>

commit d3f684f2820a7f42acef68bea6622d9032127fb2 upstream.

spi_sync call uses its spi_message parameter to keep completion information,
using a drvdata structure is not thread-safe. Use a mutex to prevent
multiple access to shared driver data.

Signed-off-by: Pavel Herrmann <morpheus.ibis@...il.com>
Acked-by: Russell King <rmk+kernel@....linux.org.uk>
Acked-by: Pavel Machek <pavel@....cz>
Acked-by: Marek Vasut <marek.vasut@...il.com>
Acked-by: Cyril Hrubis <metan@....cz>
Tested-by: Stanislav Brabec <utx@...guin.cz>
Signed-off-by: Jean Delvare <khali@...ux-fr.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@...e.de>

---
 drivers/hwmon/max1111.c |   11 +++++++++++
 1 file changed, 11 insertions(+)

--- a/drivers/hwmon/max1111.c
+++ b/drivers/hwmon/max1111.c
@@ -39,6 +39,8 @@ struct max1111_data {
 	struct spi_transfer	xfer[2];
 	uint8_t *tx_buf;
 	uint8_t *rx_buf;
+	struct mutex		drvdata_lock;
+	/* protect msg, xfer and buffers from multiple access */
 };
 
 static int max1111_read(struct device *dev, int channel)
@@ -47,6 +49,9 @@ static int max1111_read(struct device *d
 	uint8_t v1, v2;
 	int err;
 
+	/* writing to drvdata struct is not thread safe, wait on mutex */
+	mutex_lock(&data->drvdata_lock);
+
 	data->tx_buf[0] = (channel << MAX1111_CTRL_SEL_SH) |
 		MAX1111_CTRL_PD0 | MAX1111_CTRL_PD1 |
 		MAX1111_CTRL_SGL | MAX1111_CTRL_UNI | MAX1111_CTRL_STR;
@@ -54,12 +59,15 @@ static int max1111_read(struct device *d
 	err = spi_sync(data->spi, &data->msg);
 	if (err < 0) {
 		dev_err(dev, "spi_sync failed with %d\n", err);
+		mutex_unlock(&data->drvdata_lock);
 		return err;
 	}
 
 	v1 = data->rx_buf[0];
 	v2 = data->rx_buf[1];
 
+	mutex_unlock(&data->drvdata_lock);
+
 	if ((v1 & 0xc0) || (v2 & 0x3f))
 		return -EINVAL;
 
@@ -175,6 +183,8 @@ static int __devinit max1111_probe(struc
 	if (err)
 		goto err_free_data;
 
+	mutex_init(&data->drvdata_lock);
+
 	data->spi = spi;
 	spi_set_drvdata(spi, data);
 
@@ -212,6 +222,7 @@ static int __devexit max1111_remove(stru
 
 	hwmon_device_unregister(data->hwmon_dev);
 	sysfs_remove_group(&spi->dev.kobj, &max1111_attr_group);
+	mutex_destroy(&data->drvdata_lock);
 	kfree(data->rx_buf);
 	kfree(data->tx_buf);
 	kfree(data);


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