sysfs: add sysfs_file_change_owner()

Add helpers to change the owner of a sysfs files.
This function will be used to correctly account for kobject ownership
changes, e.g. when moving network devices between network namespaces.

Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Christian Brauner <christian.brauner@ubuntu.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/fs/sysfs/file.c b/fs/sysfs/file.c
index 130fc6fbcc038b8e429cffd6f34859dac4d99ea4..4ca936ca3ba4475ddeaea3749d82b881ededb7d1 100644 (file)
--- a/fs/sysfs/file.c
+++ b/fs/sysfs/file.c
@@ -558,3 +558,50 @@ void sysfs_remove_bin_file(struct kobject *kobj,
        kernfs_remove_by_name(kobj->sd, attr->attr.name);
 }
 EXPORT_SYMBOL_GPL(sysfs_remove_bin_file);
+
+static int internal_change_owner(struct kernfs_node *kn, kuid_t kuid,
+                                kgid_t kgid)
+{
+       struct iattr newattrs = {
+               .ia_valid = ATTR_UID | ATTR_GID,
+               .ia_uid = kuid,
+               .ia_gid = kgid,
+       };
+       return kernfs_setattr(kn, &newattrs);
+}
+
+/**
+ *     sysfs_file_change_owner - change owner of a sysfs file.
+ *     @kobj:  object.
+ *     @name:  name of the file to change.
+ *     @kuid:  new owner's kuid
+ *     @kgid:  new owner's kgid
+ *
+ * This function looks up the sysfs entry @name under @kobj and changes the
+ * ownership to @kuid/@kgid.
+ *
+ * Returns 0 on success or error code on failure.
+ */
+int sysfs_file_change_owner(struct kobject *kobj, const char *name, kuid_t kuid,
+                           kgid_t kgid)
+{
+       struct kernfs_node *kn;
+       int error;
+
+       if (!name)
+               return -EINVAL;
+
+       if (!kobj->state_in_sysfs)
+               return -EINVAL;
+
+       kn = kernfs_find_and_get(kobj->sd, name);
+       if (!kn)
+               return -ENOENT;
+
+       error = internal_change_owner(kn, kuid, kgid);
+
+       kernfs_put(kn);
+
+       return error;
+}
+EXPORT_SYMBOL_GPL(sysfs_file_change_owner);

diff --git a/include/linux/sysfs.h b/include/linux/sysfs.h
index fa7ee503fb76326d181d844aad22700bd85bf7fa..a7884024a91189686d218016ade7dca96891c23a 100644 (file)
--- a/include/linux/sysfs.h
+++ b/include/linux/sysfs.h
@@ -310,6 +310,9 @@ static inline void sysfs_enable_ns(struct kernfs_node *kn)
        return kernfs_enable_ns(kn);
 }
 
+int sysfs_file_change_owner(struct kobject *kobj, const char *name, kuid_t kuid,
+                           kgid_t kgid);
+
 #else /* CONFIG_SYSFS */
 
 static inline int sysfs_create_dir_ns(struct kobject *kobj, const void *ns)
@@ -522,6 +525,13 @@ static inline void sysfs_enable_ns(struct kernfs_node *kn)
 {
 }
 
+static inline int sysfs_file_change_owner(struct kobject *kobj,
+                                         const char *name, kuid_t kuid,
+                                         kgid_t kgid)
+{
+       return 0;
+}
+
 #endif /* CONFIG_SYSFS */
 
 static inline int __must_check sysfs_create_file(struct kobject *kobj,