[PATCH net 2/3] net: core: add netdev_class_has_file_ns() helper function

[Taehee Yoo <ap420073@gmail.com>]

This helper function is to check whether the class file "/sys/class/net*"
is existing or not.
In the next patch, this helper function will be used.

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>
---
 include/linux/netdevice.h |  2 +-
 net/core/net-sysfs.c      | 13 +++++++++++++
 2 files changed, 14 insertions(+), 1 deletion(-)

diff --git a/include/linux/netdevice.h b/include/linux/netdevice.h
index 6c3f7032e8d9..e32edca79e3a 100644
--- a/include/linux/netdevice.h
+++ b/include/linux/netdevice.h
@@ -4545,7 +4545,7 @@ int netdev_class_create_file_ns(const struct class_attribute *class_attr,
 				const void *ns);
 void netdev_class_remove_file_ns(const struct class_attribute *class_attr,
 				 const void *ns);
-
+bool netdev_class_has_file_ns(const char *name, const void *ns);
 static inline int netdev_class_create_file(const struct class_attribute *class_attr)
 {
 	return netdev_class_create_file_ns(class_attr, NULL);
diff --git a/net/core/net-sysfs.c b/net/core/net-sysfs.c
index 4c826b8bf9b1..78de063201bc 100644
--- a/net/core/net-sysfs.c
+++ b/net/core/net-sysfs.c
@@ -1781,6 +1781,19 @@ void netdev_class_remove_file_ns(const struct class_attribute *class_attr,
 }
 EXPORT_SYMBOL(netdev_class_remove_file_ns);
 
+bool netdev_class_has_file_ns(const char *name, const void *ns)
+{
+	struct kernfs_node *kn;
+
+	kn = class_find_and_get_file_ns(&net_class, name, ns);
+	if (kn) {
+		kernfs_put(kn);
+		return true;
+	}
+	return false;
+}
+EXPORT_SYMBOL(netdev_class_has_file_ns);
+
 int __init netdev_kobject_init(void)
 {
 	kobj_ns_type_register(&net_ns_type_operations);
-- 
2.17.1