kernfs: allow creating kernfs objects with arbitrary uid/gid

This change allows creating kernfs files and directories with arbitrary
uid/gid instead of always using GLOBAL_ROOT_UID/GID by extending
kernfs_create_dir_ns() and kernfs_create_file_ns() with uid/gid arguments.
The "simple" kernfs_create_file() and kernfs_create_dir() are left alone
and always create objects belonging to the global root.

When creating symlinks ownership (uid/gid) is taken from the target kernfs
object.

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, 19 insertions, 9 deletions

diff --git a/include/linux/kernfs.h b/include/linux/kernfs.h
index ab25c8b6d9e3..814643f7ee52 100644
--- a/include/linux/kernfs.h
+++ b/include/linux/kernfs.h
@@ -15,6 +15,7 @@
 #include <linux/lockdep.h>
 #include <linux/rbtree.h>
 #include <linux/atomic.h>
+#include <linux/uidgid.h>
 #include <linux/wait.h>
 
 struct file;
@@ -325,12 +326,14 @@ void kernfs_destroy_root(struct kernfs_root *root);
 
 struct kernfs_node *kernfs_create_dir_ns(struct kernfs_node *parent,
 					 const char *name, umode_t mode,
+					 kuid_t uid, kgid_t gid,
 					 void *priv, const void *ns);
 struct kernfs_node *kernfs_create_empty_dir(struct kernfs_node *parent,
 					    const char *name);
 struct kernfs_node *__kernfs_create_file(struct kernfs_node *parent,
-					 const char *name,
-					 umode_t mode, loff_t size,
+					 const char *name, umode_t mode,
+					 kuid_t uid, kgid_t gid,
+					 loff_t size,
 					 const struct kernfs_ops *ops,
 					 void *priv, const void *ns,
 					 struct lock_class_key *key);
@@ -415,12 +418,14 @@ static inline void kernfs_destroy_root(struct kernfs_root *root) { }
 
 static inline struct kernfs_node *
 kernfs_create_dir_ns(struct kernfs_node *parent, const char *name,
-		     umode_t mode, void *priv, const void *ns)
+		     umode_t mode, kuid_t uid, kgid_t gid,
+		     void *priv, const void *ns)
 { return ERR_PTR(-ENOSYS); }
 
 static inline struct kernfs_node *
 __kernfs_create_file(struct kernfs_node *parent, const char *name,
-		     umode_t mode, loff_t size, const struct kernfs_ops *ops,
+		     umode_t mode, kuid_t uid, kgid_t gid,
+		     loff_t size, const struct kernfs_ops *ops,
 		     void *priv, const void *ns, struct lock_class_key *key)
 { return ERR_PTR(-ENOSYS); }
 
@@ -498,12 +503,15 @@ static inline struct kernfs_node *
 kernfs_create_dir(struct kernfs_node *parent, const char *name, umode_t mode,
 		  void *priv)
 {
-	return kernfs_create_dir_ns(parent, name, mode, priv, NULL);
+	return kernfs_create_dir_ns(parent, name, mode,
+				    GLOBAL_ROOT_UID, GLOBAL_ROOT_GID,
+				    priv, NULL);
 }
 
 static inline struct kernfs_node *
 kernfs_create_file_ns(struct kernfs_node *parent, const char *name,
-		      umode_t mode, loff_t size, const struct kernfs_ops *ops,
+		      umode_t mode, kuid_t uid, kgid_t gid,
+		      loff_t size, const struct kernfs_ops *ops,
 		      void *priv, const void *ns)
 {
 	struct lock_class_key *key = NULL;
@@ -511,15 +519,17 @@ kernfs_create_file_ns(struct kernfs_node *parent, const char *name,
 #ifdef CONFIG_DEBUG_LOCK_ALLOC
 	key = (struct lock_class_key *)&ops->lockdep_key;
 #endif
-	return __kernfs_create_file(parent, name, mode, size, ops, priv, ns,
-				    key);
+	return __kernfs_create_file(parent, name, mode, uid, gid,
+				    size, ops, priv, ns, key);
 }
 
 static inline struct kernfs_node *
 kernfs_create_file(struct kernfs_node *parent, const char *name, umode_t mode,
 		   loff_t size, const struct kernfs_ops *ops, void *priv)
 {
-	return kernfs_create_file_ns(parent, name, mode, size, ops, priv, NULL);
+	return kernfs_create_file_ns(parent, name, mode,
+				     GLOBAL_ROOT_UID, GLOBAL_ROOT_GID,
+				     size, ops, priv, NULL);
 }
 
 static inline int kernfs_remove_by_name(struct kernfs_node *parent,