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

Convert to struct mnt_idmap.

Last cycle we merged the necessary infrastructure in
256c8aed ("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: NDave Chinner <dchinner@redhat.com>
Reviewed-by: NChristoph Hellwig <hch@lst.de>
Signed-off-by: NChristian Brauner (Microsoft) <brauner@kernel.org>

fs/ext4/ialloc.c

@@ -943,7 +943,6 @@ struct inode *__ext4_new_inode(struct mnt_idmap *idmap,
 	ext4_group_t flex_group;
 	struct ext4_group_info *grp = NULL;
 	bool encrypt = false;
-	struct user_namespace *mnt_userns = mnt_idmap_owner(idmap);
 
 	/* Cannot create files in a deleted directory */
 	if (!dir || !dir->i_nlink)
@@ -973,7 +972,7 @@ struct inode *__ext4_new_inode(struct mnt_idmap *idmap,
 		i_gid_write(inode, owner[1]);
 	} else if (test_opt(sb, GRPID)) {
 		inode->i_mode = mode;
-		inode_fsuid_set(inode, mnt_userns);
+		inode_fsuid_set(inode, idmap);
 		inode->i_gid = dir->i_gid;
 	} else
 		inode_init_owner(idmap, inode, dir, mode);

fs/inode.c

@@ -2293,9 +2293,7 @@ EXPORT_SYMBOL(init_special_inode);
 void inode_init_owner(struct mnt_idmap *idmap, struct inode *inode,
 		      const struct inode *dir, umode_t mode)
 {
-	struct user_namespace *mnt_userns = mnt_idmap_owner(idmap);
-
-	inode_fsuid_set(inode, mnt_userns);
+	inode_fsuid_set(inode, idmap);
 	if (dir && dir->i_mode & S_ISGID) {
 		inode->i_gid = dir->i_gid;
 
@@ -2303,7 +2301,7 @@ void inode_init_owner(struct mnt_idmap *idmap, struct inode *inode,
 		if (S_ISDIR(mode))
 			mode |= S_ISGID;
 	} else
-		inode_fsgid_set(inode, mnt_userns);
+		inode_fsgid_set(inode, idmap);
 	inode->i_mode = mode;
 }
 EXPORT_SYMBOL(inode_init_owner);

fs/xfs/xfs_inode.c

@@ -788,7 +788,6 @@ xfs_init_new_inode(
 	bool			init_xattrs,
 	struct xfs_inode	**ipp)
 {
-	struct user_namespace	*mnt_userns = mnt_idmap_owner(idmap);
 	struct inode		*dir = pip ? VFS_I(pip) : NULL;
 	struct xfs_mount	*mp = tp->t_mountp;
 	struct xfs_inode	*ip;
@@ -824,7 +823,7 @@ xfs_init_new_inode(
 	ip->i_projid = prid;
 
 	if (dir && !(dir->i_mode & S_ISGID) && xfs_has_grpid(mp)) {
-		inode_fsuid_set(inode, mnt_userns);
+		inode_fsuid_set(inode, idmap);
 		inode->i_gid = dir->i_gid;
 		inode->i_mode = mode;
 	} else {
@@ -955,7 +954,6 @@ xfs_create(
 	bool			init_xattrs,
 	xfs_inode_t		**ipp)
 {
-	struct user_namespace	*mnt_userns = mnt_idmap_owner(idmap);
 	int			is_dir = S_ISDIR(mode);
 	struct xfs_mount	*mp = dp->i_mount;
 	struct xfs_inode	*ip = NULL;
@@ -980,8 +978,8 @@ xfs_create(
 	/*
 	 * Make sure that we have allocated dquot(s) on disk.
 	 */
-	error = xfs_qm_vop_dqalloc(dp, mapped_fsuid(mnt_userns, &init_user_ns),
-			mapped_fsgid(mnt_userns, &init_user_ns), prid,
+	error = xfs_qm_vop_dqalloc(dp, mapped_fsuid(idmap, &init_user_ns),
+			mapped_fsgid(idmap, &init_user_ns), prid,
 			XFS_QMOPT_QUOTALL | XFS_QMOPT_INHERIT,
 			&udqp, &gdqp, &pdqp);
 	if (error)
@@ -1109,7 +1107,6 @@ xfs_create_tmpfile(
 	umode_t			mode,
 	struct xfs_inode	**ipp)
 {
-	struct user_namespace	*mnt_userns = mnt_idmap_owner(idmap);
 	struct xfs_mount	*mp = dp->i_mount;
 	struct xfs_inode	*ip = NULL;
 	struct xfs_trans	*tp = NULL;
@@ -1130,8 +1127,8 @@ xfs_create_tmpfile(
 	/*
 	 * Make sure that we have allocated dquot(s) on disk.
 	 */
-	error = xfs_qm_vop_dqalloc(dp, mapped_fsuid(mnt_userns, &init_user_ns),
-			mapped_fsgid(mnt_userns, &init_user_ns), prid,
+	error = xfs_qm_vop_dqalloc(dp, mapped_fsuid(idmap, &init_user_ns),
+			mapped_fsgid(idmap, &init_user_ns), prid,
 			XFS_QMOPT_QUOTALL | XFS_QMOPT_INHERIT,
 			&udqp, &gdqp, &pdqp);
 	if (error)

fs/xfs/xfs_symlink.c

@@ -151,7 +151,6 @@ xfs_symlink(
 	umode_t			mode,
 	struct xfs_inode	**ipp)
 {
-	struct user_namespace	*mnt_userns = mnt_idmap_owner(idmap);
 	struct xfs_mount	*mp = dp->i_mount;
 	struct xfs_trans	*tp = NULL;
 	struct xfs_inode	*ip = NULL;
@@ -194,8 +193,8 @@ xfs_symlink(
 	/*
 	 * Make sure that we have allocated dquot(s) on disk.
 	 */
-	error = xfs_qm_vop_dqalloc(dp, mapped_fsuid(mnt_userns, &init_user_ns),
-			mapped_fsgid(mnt_userns, &init_user_ns), prid,
+	error = xfs_qm_vop_dqalloc(dp, mapped_fsuid(idmap, &init_user_ns),
+			mapped_fsgid(idmap, &init_user_ns), prid,
 			XFS_QMOPT_QUOTALL | XFS_QMOPT_INHERIT,
 			&udqp, &gdqp, &pdqp);
 	if (error)

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) &&

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()));
 }