[PATCH 4.4 03/57] driver core: platform: fix race condition with driver_override

[Greg Kroah-Hartman]

4.4-stable review patch.  If anyone has any objections, please let me know.

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

From: Adrian Salido <sali...@google.com>

commit 6265539776a0810b7ce6398c27866ddb9c6bd154 upstream.

The driver_override implementation is susceptible to race condition when
different threads are reading vs storing a different driver override.
Add locking to avoid race condition.

Fixes: 3d713e0e382e ("driver core: platform: add device binding path 
'driver_override'")
Cc: sta...@vger.kernel.org
Signed-off-by: Adrian Salido <sali...@google.com>
Signed-off-by: Greg Kroah-Hartman <gre...@linuxfoundation.org>

---
 drivers/base/platform.c |   11 +++++++++--
 1 file changed, 9 insertions(+), 2 deletions(-)

--- a/drivers/base/platform.c
+++ b/drivers/base/platform.c
@@ -807,7 +807,7 @@ static ssize_t driver_override_store(str
                                     const char *buf, size_t count)
 {
        struct platform_device *pdev = to_platform_device(dev);
-       char *driver_override, *old = pdev->driver_override, *cp;
+       char *driver_override, *old, *cp;
 
        if (count > PATH_MAX)
                return -EINVAL;
@@ -820,12 +820,15 @@ static ssize_t driver_override_store(str
        if (cp)
                *cp = '\0';
 
+       device_lock(dev);
+       old = pdev->driver_override;
        if (strlen(driver_override)) {
                pdev->driver_override = driver_override;
        } else {
                kfree(driver_override);
                pdev->driver_override = NULL;
        }
+       device_unlock(dev);
 
        kfree(old);
 
@@ -836,8 +839,12 @@ static ssize_t driver_override_show(stru
                                    struct device_attribute *attr, char *buf)
 {
        struct platform_device *pdev = to_platform_device(dev);
+       ssize_t len;
 
-       return sprintf(buf, "%s\n", pdev->driver_override);
+       device_lock(dev);
+       len = sprintf(buf, "%s\n", pdev->driver_override);
+       device_unlock(dev);
+       return len;
 }
 static DEVICE_ATTR_RW(driver_override);