1 files changed, 81 insertions, 2 deletions

diff --git a/drivers/base/devcoredump.c b/drivers/base/devcoredump.c
index f1a3353f3494..1ba4af7f2f21 100644
--- a/drivers/base/devcoredump.c
+++ b/drivers/base/devcoredump.c
@@ -29,6 +29,47 @@ struct devcd_entry {
 	struct device devcd_dev;
 	void *data;
 	size_t datalen;
+	/*
+	 * Here, mutex is required to serialize the calls to del_wk work between
+	 * user/kernel space which happens when devcd is added with device_add()
+	 * and that sends uevent to user space. User space reads the uevents,
+	 * and calls to devcd_data_write() which try to modify the work which is
+	 * not even initialized/queued from devcoredump.
+	 *
+	 *
+	 *
+	 *        cpu0(X)                                 cpu1(Y)
+	 *
+	 *        dev_coredump() uevent sent to user space
+	 *        device_add()  ======================> user space process Y reads the
+	 *                                              uevents writes to devcd fd
+	 *                                              which results into writes to
+	 *
+	 *                                             devcd_data_write()
+	 *                                               mod_delayed_work()
+	 *                                                 try_to_grab_pending()
+	 *                                                   del_timer()
+	 *                                                     debug_assert_init()
+	 *       INIT_DELAYED_WORK()
+	 *       schedule_delayed_work()
+	 *
+	 *
+	 * Also, mutex alone would not be enough to avoid scheduling of
+	 * del_wk work after it get flush from a call to devcd_free()
+	 * mentioned as below.
+	 *
+	 *	disabled_store()
+	 *        devcd_free()
+	 *          mutex_lock()             devcd_data_write()
+	 *          flush_delayed_work()
+	 *          mutex_unlock()
+	 *                                   mutex_lock()
+	 *                                   mod_delayed_work()
+	 *                                   mutex_unlock()
+	 * So, delete_work flag is required.
+	 */
+	struct mutex mutex;
+	bool delete_work;
 	struct module *owner;
 	ssize_t (*read)(char *buffer, loff_t offset, size_t count,
 			void *data, size_t datalen);
@@ -88,7 +129,12 @@ static ssize_t devcd_data_write(struct file *filp, struct kobject *kobj,
 	struct device *dev = kobj_to_dev(kobj);
 	struct devcd_entry *devcd = dev_to_devcd(dev);
 
-	mod_delayed_work(system_wq, &devcd->del_wk, 0);
+	mutex_lock(&devcd->mutex);
+	if (!devcd->delete_work) {
+		devcd->delete_work = true;
+		mod_delayed_work(system_wq, &devcd->del_wk, 0);
+	}
+	mutex_unlock(&devcd->mutex);
 
 	return count;
 }
@@ -116,7 +162,12 @@ static int devcd_free(struct device *dev, void *data)
 {
 	struct devcd_entry *devcd = dev_to_devcd(dev);
 
+	mutex_lock(&devcd->mutex);
+	if (!devcd->delete_work)
+		devcd->delete_work = true;
+
 	flush_delayed_work(&devcd->del_wk);
+	mutex_unlock(&devcd->mutex);
 	return 0;
 }
 
@@ -126,6 +177,30 @@ static ssize_t disabled_show(struct class *class, struct class_attribute *attr,
 	return sprintf(buf, "%d\n", devcd_disabled);
 }
 
+/*
+ *
+ *	disabled_store()                                	worker()
+ *	 class_for_each_device(&devcd_class,
+ *		NULL, NULL, devcd_free)
+ *         ...
+ *         ...
+ *	   while ((dev = class_dev_iter_next(&iter))
+ *                                                             devcd_del()
+ *                                                               device_del()
+ *                                                                 put_device() <- last reference
+ *             error = fn(dev, data)                           devcd_dev_release()
+ *             devcd_free(dev, data)                           kfree(devcd)
+ *             mutex_lock(&devcd->mutex);
+ *
+ *
+ * In the above diagram, It looks like disabled_store() would be racing with parallely
+ * running devcd_del() and result in memory abort while acquiring devcd->mutex which
+ * is called after kfree of devcd memory  after dropping its last reference with
+ * put_device(). However, this will not happens as fn(dev, data) runs
+ * with its own reference to device via klist_node so it is not its last reference.
+ * so, above situation would not occur.
+ */
+
 static ssize_t disabled_store(struct class *class, struct class_attribute *attr,
 			      const char *buf, size_t count)
 {
@@ -291,13 +366,16 @@ void dev_coredumpm(struct device *dev, struct module *owner,
 	devcd->read = read;
 	devcd->free = free;
 	devcd->failing_dev = get_device(dev);
+	devcd->delete_work = false;
 
+	mutex_init(&devcd->mutex);
 	device_initialize(&devcd->devcd_dev);
 
 	dev_set_name(&devcd->devcd_dev, "devcd%d",
 		     atomic_inc_return(&devcd_count));
 	devcd->devcd_dev.class = &devcd_class;
 
+	mutex_lock(&devcd->mutex);
 	if (device_add(&devcd->devcd_dev))
 		goto put_device;
 
@@ -311,10 +389,11 @@ void dev_coredumpm(struct device *dev, struct module *owner,
 
 	INIT_DELAYED_WORK(&devcd->del_wk, devcd_del);
 	schedule_delayed_work(&devcd->del_wk, DEVCD_TIMEOUT);
-
+	mutex_unlock(&devcd->mutex);
 	return;
  put_device:
 	put_device(&devcd->devcd_dev);
+	mutex_unlock(&devcd->mutex);
  put_module:
 	module_put(owner);
  free: