fs: port fs{g,u}id helpers to mnt_idmap

Convert to struct mnt_idmap.

Last cycle we merged the necessary infrastructure in
256c8aed2b42 ("fs: introduce dedicated idmap type for mounts").
This is just the conversion to struct mnt_idmap.

Currently we still pass around the plain namespace that was attached to a
mount. This is in general pretty convenient but it makes it easy to
conflate namespaces that are relevant on the filesystem with namespaces
that are relevent on the mount level. Especially for non-vfs developers
without detailed knowledge in this area this can be a potential source for
bugs.

Once the conversion to struct mnt_idmap is done all helpers down to the
really low-level helpers will take a struct mnt_idmap argument instead of
two namespace arguments. This way it becomes impossible to conflate the two
eliminating the possibility of any bugs. All of the vfs and all filesystems
only operate on struct mnt_idmap.

Acked-by: Dave Chinner <[email protected]>
Reviewed-by: Christoph Hellwig <[email protected]>
Signed-off-by: Christian Brauner (Microsoft) <[email protected]>

2 files changed, 20 insertions, 19 deletions

diff --git a/include/linux/fs.h b/include/linux/fs.h
index 173c5274a63a..54a95ed68322 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -1744,29 +1744,29 @@ static inline void i_gid_update(struct mnt_idmap *idmap,
 /**
  * inode_fsuid_set - initialize inode's i_uid field with callers fsuid
  * @inode: inode to initialize
- * @mnt_userns: user namespace of the mount the inode was found from
+ * @idmap: idmap of the mount the inode was found from
  *
  * Initialize the i_uid field of @inode. If the inode was found/created via
- * an idmapped mount map the caller's fsuid according to @mnt_users.
+ * an idmapped mount map the caller's fsuid according to @idmap.
  */
 static inline void inode_fsuid_set(struct inode *inode,
-				   struct user_namespace *mnt_userns)
+				   struct mnt_idmap *idmap)
 {
-	inode->i_uid = mapped_fsuid(mnt_userns, i_user_ns(inode));
+	inode->i_uid = mapped_fsuid(idmap, i_user_ns(inode));
 }
 
 /**
  * inode_fsgid_set - initialize inode's i_gid field with callers fsgid
  * @inode: inode to initialize
- * @mnt_userns: user namespace of the mount the inode was found from
+ * @idmap: idmap of the mount the inode was found from
  *
  * Initialize the i_gid field of @inode. If the inode was found/created via
- * an idmapped mount map the caller's fsgid according to @mnt_users.
+ * an idmapped mount map the caller's fsgid according to @idmap.
  */
 static inline void inode_fsgid_set(struct inode *inode,
-				   struct user_namespace *mnt_userns)
+				   struct mnt_idmap *idmap)
 {
-	inode->i_gid = mapped_fsgid(mnt_userns, i_user_ns(inode));
+	inode->i_gid = mapped_fsgid(idmap, i_user_ns(inode));
 }
 
 /**
@@ -1784,14 +1784,13 @@ static inline bool fsuidgid_has_mapping(struct super_block *sb,
 					struct mnt_idmap *idmap)
 {
 	struct user_namespace *fs_userns = sb->s_user_ns;
-	struct user_namespace *mnt_userns = mnt_idmap_owner(idmap);
 	kuid_t kuid;
 	kgid_t kgid;
 
-	kuid = mapped_fsuid(mnt_userns, fs_userns);
+	kuid = mapped_fsuid(idmap, fs_userns);
 	if (!uid_valid(kuid))
 		return false;
-	kgid = mapped_fsgid(mnt_userns, fs_userns);
+	kgid = mapped_fsgid(idmap, fs_userns);
 	if (!gid_valid(kgid))
 		return false;
 	return kuid_has_mapping(fs_userns, kuid) &&
diff --git a/include/linux/mnt_idmapping.h b/include/linux/mnt_idmapping.h
index 0ccca33a7a6d..d63e7c84a389 100644
--- a/include/linux/mnt_idmapping.h
+++ b/include/linux/mnt_idmapping.h
@@ -375,8 +375,8 @@ static inline kgid_t vfsgid_into_kgid(vfsgid_t vfsgid)
 }
 
 /**
- * mapped_fsuid - return caller's fsuid mapped up into a mnt_userns
- * @mnt_userns: the mount's idmapping
+ * mapped_fsuid - return caller's fsuid mapped according to an idmapping
+ * @idmap: the mount's idmapping
  * @fs_userns: the filesystem's idmapping
  *
  * Use this helper to initialize a new vfs or filesystem object based on
@@ -385,18 +385,19 @@ static inline kgid_t vfsgid_into_kgid(vfsgid_t vfsgid)
  * O_CREAT. Other examples include the allocation of quotas for a specific
  * user.
  *
- * Return: the caller's current fsuid mapped up according to @mnt_userns.
+ * Return: the caller's current fsuid mapped up according to @idmap.
  */
-static inline kuid_t mapped_fsuid(struct user_namespace *mnt_userns,
+static inline kuid_t mapped_fsuid(struct mnt_idmap *idmap,
 				  struct user_namespace *fs_userns)
 {
+	struct user_namespace *mnt_userns = mnt_idmap_owner(idmap);
 	return from_vfsuid(mnt_userns, fs_userns,
 			   VFSUIDT_INIT(current_fsuid()));
 }
 
 /**
- * mapped_fsgid - return caller's fsgid mapped up into a mnt_userns
- * @mnt_userns: the mount's idmapping
+ * mapped_fsgid - return caller's fsgid mapped according to an idmapping
+ * @idmap: the mount's idmapping
  * @fs_userns: the filesystem's idmapping
  *
  * Use this helper to initialize a new vfs or filesystem object based on
@@ -405,11 +406,12 @@ static inline kuid_t mapped_fsuid(struct user_namespace *mnt_userns,
  * O_CREAT. Other examples include the allocation of quotas for a specific
  * user.
  *
- * Return: the caller's current fsgid mapped up according to @mnt_userns.
+ * Return: the caller's current fsgid mapped up according to @idmap.
  */
-static inline kgid_t mapped_fsgid(struct user_namespace *mnt_userns,
+static inline kgid_t mapped_fsgid(struct mnt_idmap *idmap,
 				  struct user_namespace *fs_userns)
 {
+	struct user_namespace *mnt_userns = mnt_idmap_owner(idmap);
 	return from_vfsgid(mnt_userns, fs_userns,
 			   VFSGIDT_INIT(current_fsgid()));
 }