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[v2] MAX1111: Fix Race condition causing NULL pointer exception

Message ID 1307131203-10845-1-git-send-email-morpheus.ibis@gmail.com (mailing list archive)
State New, archived
Headers show

Commit Message

Pavel Herrmann June 3, 2011, 8 p.m. UTC 
spi_sync call uses its spi_message parameter to keep completion information,
having this structure static is not thread-safe, potentially causing one
thread having pointers to memory on or above other threads stack. use mutex
to prevent multiple access

Signed-off-by: Pavel Herrmann <morpheus.ibis@gmail.com>
Acked-by: Russell King <rmk+kernel@arm.linux.org.uk>
Acked-by: Pavel Machek <pavel@ucw.cz>
Acked-by: Marek Vasut <marek.vasut@gmail.com>
Acked-by: Cyril Hrubis <metan@ucw.cz>

---
 drivers/hwmon/max1111.c |   12 ++++++++++++
 1 files changed, 12 insertions(+), 0 deletions(-)

Comments

Greg KH June 3, 2011, 10:32 p.m. UTC | #1 
On Fri, Jun 03, 2011 at 10:00:03PM +0200, Pavel Herrmann wrote:
> spi_sync call uses its spi_message parameter to keep completion information,
> having this structure static is not thread-safe, potentially causing one
> thread having pointers to memory on or above other threads stack. use mutex
> to prevent multiple access
> 
> Signed-off-by: Pavel Herrmann <morpheus.ibis@gmail.com>
> Acked-by: Russell King <rmk+kernel@arm.linux.org.uk>
> Acked-by: Pavel Machek <pavel@ucw.cz>
> Acked-by: Marek Vasut <marek.vasut@gmail.com>
> Acked-by: Cyril Hrubis <metan@ucw.cz>
> 
> ---
>  drivers/hwmon/max1111.c |   12 ++++++++++++
>  1 files changed, 12 insertions(+), 0 deletions(-)
>


<formletter>

This is not the correct way to submit patches for inclusion in the
stable kernel tree.  Please read Documentation/stable_kernel_rules.txt
for how to do this properly.

</formletter>
diff mbox

Patch

diff --git a/drivers/hwmon/max1111.c b/drivers/hwmon/max1111.c
index 12a54aa..d872f57 100644
--- a/drivers/hwmon/max1111.c
+++ b/drivers/hwmon/max1111.c
@@ -40,6 +40,7 @@  struct max1111_data {
 	struct spi_transfer	xfer[2];
 	uint8_t *tx_buf;
 	uint8_t *rx_buf;
+	struct mutex		msg_lock_mutex;
 };
 
 static int max1111_read(struct device *dev, int channel)
@@ -48,6 +49,11 @@  static int max1111_read(struct device *dev, int channel)
 	uint8_t v1, v2;
 	int err;
 
+	/* spi_sync requires data not to be freed before function returns
+	 * for static data, any access is dangerous, use locks
+	 */
+	mutex_lock(&data->msg_lock_mutex);
+
 	data->tx_buf[0] = (channel << MAX1111_CTRL_SEL_SH) |
 		MAX1111_CTRL_PD0 | MAX1111_CTRL_PD1 |
 		MAX1111_CTRL_SGL | MAX1111_CTRL_UNI | MAX1111_CTRL_STR;
@@ -55,12 +61,15 @@  static int max1111_read(struct device *dev, int channel)
 	err = spi_sync(data->spi, &data->msg);
 	if (err < 0) {
 		dev_err(dev, "spi_sync failed with %d\n", err);
+		mutex_unlock(&data->msg_lock_mutex);
 		return err;
 	}
 
 	v1 = data->rx_buf[0];
 	v2 = data->rx_buf[1];
 
+	mutex_unlock(&data->msg_lock_mutex);
+
 	if ((v1 & 0xc0) || (v2 & 0x3f))
 		return -EINVAL;
 
@@ -176,6 +185,8 @@  static int __devinit max1111_probe(struct spi_device *spi)
 	if (err)
 		goto err_free_data;
 
+	mutex_init(&data->msg_lock_mutex);
+
 	data->spi = spi;
 	spi_set_drvdata(spi, data);
 
@@ -213,6 +224,7 @@  static int __devexit max1111_remove(struct spi_device *spi)
 
 	hwmon_device_unregister(data->hwmon_dev);
 	sysfs_remove_group(&spi->dev.kobj, &max1111_attr_group);
+	mutex_destroy(data->msg_lock_mutex);
 	kfree(data->rx_buf);
 	kfree(data->tx_buf);
 	kfree(data);