[PATCH] driver core: access dev->driver under dev->mutex in dev_uevent

[ashishsangwan2]

From: Ashish Sangwan <a.sangwan@xxxxxxxxxxx>

We have hit a race condition while parallely accessing device's uevent
and rmmoding device's driver. In dev_uevent() first dev->driver is checked if
present which becomes true but before calling add_uevent_var 
dev->driver is set to NULL and driver is freed in __device_release_driver().
This results in either NULL pointer derefrence or invalid virtual address
access. Fix this race by accessing dev->driver under dev->mutex.

Signed-off-by: Ashish Sangwan <a.sangwan@xxxxxxxxxxx>
Signed-off-by: Namjae Jeon <namjae.jeon@xxxxxxxxxxx>
---
 drivers/base/core.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/drivers/base/core.c b/drivers/base/core.c
index 97e2baf..f8e854a 100644
--- a/drivers/base/core.c
+++ b/drivers/base/core.c
@@ -326,8 +326,15 @@ static int dev_uevent(struct kset *kset, struct kobject *kobj,
 	if (dev->type && dev->type->name)
 		add_uevent_var(env, "DEVTYPE=%s", dev->type->name);
 
+	/*
+	 * dev->driver is set NULL under dev->mutex so it should be checked
+	 * after acquiring dev->mutex. This prevents a race between 
+	 * __device_release_driver and dev_uevent.
+	 */
+	device_lock(dev);
 	if (dev->driver)
 		add_uevent_var(env, "DRIVER=%s", dev->driver->name);
+	device_unlock(dev);
 
 	/* Add common DT information about the device */
 	of_device_uevent(dev, env);
-- 
1.7.11.4

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