sysfs, kobject: allow creating kobject belonging to arbitrary users

Normally kobjects and their sysfs representation belong to global root,
however it is not necessarily the case for objects in separate namespaces.
For example, objects in separate network namespace logically belong to the
container's root and not global root.

This change lays groundwork for allowing network namespace objects
ownership to be transferred to container's root user by defining
get_ownership() callback in ktype structure and using it in sysfs code to
retrieve desired uid/gid when creating sysfs objects for given kobject.

Co-Developed-by: Tyler Hicks <tyhicks@canonical.com>
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>
Signed-off-by: Tyler Hicks <tyhicks@canonical.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 20 insertions, 12 deletions

diff --git a/fs/sysfs/file.c b/fs/sysfs/file.c
index 513fa691ecbd..fa46216523cf 100644
--- a/fs/sysfs/file.c
+++ b/fs/sysfs/file.c
@@ -245,7 +245,7 @@ static const struct kernfs_ops sysfs_bin_kfops_mmap = {
 
 int sysfs_add_file_mode_ns(struct kernfs_node *parent,
 			   const struct attribute *attr, bool is_bin,
-			   umode_t mode, const void *ns)
+			   umode_t mode, kuid_t uid, kgid_t gid, const void *ns)
 {
 	struct lock_class_key *key = NULL;
 	const struct kernfs_ops *ops;
@@ -302,8 +302,8 @@ int sysfs_add_file_mode_ns(struct kernfs_node *parent,
 	if (!attr->ignore_lockdep)
 		key = attr->key ?: (struct lock_class_key *)&attr->skey;
 #endif
-	kn = __kernfs_create_file(parent, attr->name,
-				  mode & 0777, GLOBAL_ROOT_UID, GLOBAL_ROOT_GID,
+
+	kn = __kernfs_create_file(parent, attr->name, mode & 0777, uid, gid,
 				  size, ops, (void *)attr, ns, key);
 	if (IS_ERR(kn)) {
 		if (PTR_ERR(kn) == -EEXIST)
@@ -313,12 +313,6 @@ int sysfs_add_file_mode_ns(struct kernfs_node *parent,
 	return 0;
 }
 
-int sysfs_add_file(struct kernfs_node *parent, const struct attribute *attr,
-		   bool is_bin)
-{
-	return sysfs_add_file_mode_ns(parent, attr, is_bin, attr->mode, NULL);
-}
-
 /**
  * sysfs_create_file_ns - create an attribute file for an object with custom ns
  * @kobj: object we're creating for
@@ -328,9 +322,14 @@ int sysfs_add_file(struct kernfs_node *parent, const struct attribute *attr,
 int sysfs_create_file_ns(struct kobject *kobj, const struct attribute *attr,
 			 const void *ns)
 {
+	kuid_t uid;
+	kgid_t gid;
+
 	BUG_ON(!kobj || !kobj->sd || !attr);
 
-	return sysfs_add_file_mode_ns(kobj->sd, attr, false, attr->mode, ns);
+	kobject_get_ownership(kobj, &uid, &gid);
+	return sysfs_add_file_mode_ns(kobj->sd, attr, false, attr->mode,
+				      uid, gid, ns);
 
 }
 EXPORT_SYMBOL_GPL(sysfs_create_file_ns);
@@ -359,6 +358,8 @@ int sysfs_add_file_to_group(struct kobject *kobj,
 		const struct attribute *attr, const char *group)
 {
 	struct kernfs_node *parent;
+	kuid_t uid;
+	kgid_t gid;
 	int error;
 
 	if (group) {
@@ -371,7 +372,9 @@ int sysfs_add_file_to_group(struct kobject *kobj,
 	if (!parent)
 		return -ENOENT;
 
-	error = sysfs_add_file(parent, attr, false);
+	kobject_get_ownership(kobj, &uid, &gid);
+	error = sysfs_add_file_mode_ns(kobj->sd, attr, false,
+				       attr->mode, uid, gid, NULL);
 	kernfs_put(parent);
 
 	return error;
@@ -487,9 +490,14 @@ EXPORT_SYMBOL_GPL(sysfs_remove_file_from_group);
 int sysfs_create_bin_file(struct kobject *kobj,
 			  const struct bin_attribute *attr)
 {
+	kuid_t uid;
+	kgid_t gid;
+
 	BUG_ON(!kobj || !kobj->sd || !attr);
 
-	return sysfs_add_file(kobj->sd, &attr->attr, true);
+	kobject_get_ownership(kobj, &uid, &gid);
+	return sysfs_add_file_mode_ns(kobj->sd, &attr->attr, true,
+				      attr->attr.mode, uid, gid, NULL);
 }
 EXPORT_SYMBOL_GPL(sysfs_create_bin_file);