regmap: debugfs: fix possbile NULL pointer dereference

commit 2c98e0c1 upstream.

If 'map->dev' is NULL and there will lead dev_name() to be NULL pointer
dereference. So before dev_name(), we need to have check of the map->dev
pionter.

We also should make sure that the 'name' pointer shouldn't be NULL for
debugfs_create_dir(). So here using one default "dummy" debugfs name when
the 'name' pointer and 'map->dev' are both NULL.
Signed-off-by: Xiubo Li <Li.Xiubo@freescale.com>
Signed-off-by: Mark Brown <broonie@kernel.org>
[lizf: Backported to 3.4: dev_name() is passed to debugfs_create_dir() in 3.4]
Signed-off-by: Zefan Li <lizefan@huawei.com>

drivers/base/regmap/regmap-debugfs.c

@@ -244,7 +244,12 @@ static const struct file_operations regmap_access_fops = {
 
 void regmap_debugfs_init(struct regmap *map)
 {
-	map->debugfs = debugfs_create_dir(dev_name(map->dev),
+	const char *devname = "dummy";
+
+	if (map->dev)
+		devname = dev_name(map->dev);
+
+	map->debugfs = debugfs_create_dir(devname,
 					  regmap_debugfs_root);
 	if (!map->debugfs) {
 		dev_warn(map->dev, "Failed to create debugfs directory\n");