[PATCH] [18/50] hwmon: (max1111) Fix race condition causing NULL pointer

Andi Kleen
2011-07-28T23:53:33Z

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

[ upstream commit d3f684f2820a7f42acef68bea6622d9032127fb2 ]
exception

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@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>
Tested-by: Stanislav Brabec <utx@penguin.cz>
Signed-off-by: Jean Delvare <khali@linux-fr.org>
Cc: stable@kernel.org
Signed-off-by: Andi Kleen <ak@linux.intel.com>

Index: linux-2.6.35.y/drivers/hwmon/max1111.c
===================================================================
--- linux-2.6.35.y.orig/drivers/hwmon/max1111.c
+++ linux-2.6.35.y/drivers/hwmon/max1111.c
@@ -40,6 +40,8 @@ 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)
@@ -48,6 +50,9 @@ 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;
@@ -55,12 +60,15 @@ 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;

@@ -176,6 +184,8 @@ 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);

@@ -213,6 +223,7 @@ 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);