[PATCH RESEND net 1/3] class: add class_find_and_get_file_ns() helper function

[Taehee Yoo <ap420073@gmail.com>]

The new helper function is to find and get a class file.
This function is useful for checking whether the class file is existing
or not. This function will be used by networking stack to
check "/sys/class/net/*" file.

Reported-by: syzbot+830c6dbfc71edc4f0b8f@syzkaller.appspotmail.com
Fixes: b76cdba9cdb2 ("[PATCH] bonding: add sysfs functionality to bonding (large)")
Signed-off-by: Taehee Yoo <ap420073@gmail.com>
---
 drivers/base/class.c         | 12 ++++++++++++
 include/linux/device/class.h |  4 +++-
 2 files changed, 15 insertions(+), 1 deletion(-)

diff --git a/drivers/base/class.c b/drivers/base/class.c
index bcd410e6d70a..dedf41f32f0d 100644
--- a/drivers/base/class.c
+++ b/drivers/base/class.c
@@ -105,6 +105,17 @@ void class_remove_file_ns(struct class *cls, const struct class_attribute *attr,
 		sysfs_remove_file_ns(&cls->p->subsys.kobj, &attr->attr, ns);
 }
 
+struct kernfs_node *class_find_and_get_file_ns(struct class *cls,
+					       const char *name,
+					       const void *ns)
+{
+	struct kernfs_node *kn = NULL;
+
+	if (cls)
+		kn = kernfs_find_and_get_ns(cls->p->subsys.kobj.sd, name, ns);
+	return kn;
+}
+
 static struct class *class_get(struct class *cls)
 {
 	if (cls)
@@ -580,6 +591,7 @@ int __init classes_init(void)
 
 EXPORT_SYMBOL_GPL(class_create_file_ns);
 EXPORT_SYMBOL_GPL(class_remove_file_ns);
+EXPORT_SYMBOL_GPL(class_find_and_get_file_ns);
 EXPORT_SYMBOL_GPL(class_unregister);
 EXPORT_SYMBOL_GPL(class_destroy);
 
diff --git a/include/linux/device/class.h b/include/linux/device/class.h
index e8d470c457d1..230cf2ce6d3f 100644
--- a/include/linux/device/class.h
+++ b/include/linux/device/class.h
@@ -209,7 +209,9 @@ extern int __must_check class_create_file_ns(struct class *class,
 extern void class_remove_file_ns(struct class *class,
 				 const struct class_attribute *attr,
 				 const void *ns);
-
+struct kernfs_node *class_find_and_get_file_ns(struct class *cls,
+					       const char *name,
+					       const void *ns);
 static inline int __must_check class_create_file(struct class *class,
 					const struct class_attribute *attr)
 {
-- 
2.17.1