fs: port higher-level mapping helpers

Enable the mapped_fs{g,u}id() helpers to support filesystems mounted
with an idmapping. Apart from core mapping helpers that use
mapped_fs{g,u}id() to initialize struct inode's i_{g,u}id fields xfs is
the only place that uses these low-level helpers directly.

The patch only extends the helpers to be able to take the filesystem
idmapping into account. Since we don't actually yet pass the
filesystem's idmapping in no functional changes happen. This will happen
in a final patch.

Link: https://lore.kernel.org/r/20211123114227.3124056-9-brauner@kernel.org (v1)
Link: https://lore.kernel.org/r/20211130121032.3753852-9-brauner@kernel.org (v2)
Link: https://lore.kernel.org/r/20211203111707.3901969-9-brauner@kernel.org
Cc: Seth Forshee <sforshee@digitalocean.com>
Cc: Christoph Hellwig <hch@lst.de>
Cc: Al Viro <viro@zeniv.linux.org.uk>
CC: linux-fsdevel@vger.kernel.org
Reviewed-by: Amir Goldstein <amir73il@gmail.com>
Reviewed-by: Seth Forshee <sforshee@digitalocean.com>
Signed-off-by: Christian Brauner <christian.brauner@ubuntu.com>

fs/xfs/xfs_inode.c

@@ -988,8 +988,8 @@ xfs_create(
 	/*
 	 * Make sure that we have allocated dquot(s) on disk.
 	 */
-	error = xfs_qm_vop_dqalloc(dp, mapped_fsuid(mnt_userns),
-			mapped_fsgid(mnt_userns), prid,
+	error = xfs_qm_vop_dqalloc(dp, mapped_fsuid(mnt_userns, &init_user_ns),
+			mapped_fsgid(mnt_userns, &init_user_ns), prid,
 			XFS_QMOPT_QUOTALL | XFS_QMOPT_INHERIT,
 			&udqp, &gdqp, &pdqp);
 	if (error)
@@ -1142,8 +1142,8 @@ xfs_create_tmpfile(
 	/*
 	 * Make sure that we have allocated dquot(s) on disk.
 	 */
-	error = xfs_qm_vop_dqalloc(dp, mapped_fsuid(mnt_userns),
-			mapped_fsgid(mnt_userns), prid,
+	error = xfs_qm_vop_dqalloc(dp, mapped_fsuid(mnt_userns, &init_user_ns),
+			mapped_fsgid(mnt_userns, &init_user_ns), prid,
 			XFS_QMOPT_QUOTALL | XFS_QMOPT_INHERIT,
 			&udqp, &gdqp, &pdqp);
 	if (error)

fs/xfs/xfs_symlink.c

@@ -184,8 +184,8 @@ xfs_symlink(
 	/*
 	 * Make sure that we have allocated dquot(s) on disk.
 	 */
-	error = xfs_qm_vop_dqalloc(dp, mapped_fsuid(mnt_userns),
-			mapped_fsgid(mnt_userns), prid,
+	error = xfs_qm_vop_dqalloc(dp, mapped_fsuid(mnt_userns, &init_user_ns),
+			mapped_fsgid(mnt_userns, &init_user_ns), prid,
 			XFS_QMOPT_QUOTALL | XFS_QMOPT_INHERIT,
 			&udqp, &gdqp, &pdqp);
 	if (error)

include/linux/fs.h

@@ -1664,7 +1664,7 @@ static inline kgid_t i_gid_into_mnt(struct user_namespace *mnt_userns,
 static inline void inode_fsuid_set(struct inode *inode,
 				   struct user_namespace *mnt_userns)
 {
-	inode->i_uid = mapped_fsuid(mnt_userns);
+	inode->i_uid = mapped_fsuid(mnt_userns, &init_user_ns);
 }
 
 /**
@@ -1678,7 +1678,7 @@ static inline void inode_fsuid_set(struct inode *inode,
 static inline void inode_fsgid_set(struct inode *inode,
 				   struct user_namespace *mnt_userns)
 {
-	inode->i_gid = mapped_fsgid(mnt_userns);
+	inode->i_gid = mapped_fsgid(mnt_userns, &init_user_ns);
 }
 
 /**
@@ -1699,10 +1699,10 @@ static inline bool fsuidgid_has_mapping(struct super_block *sb,
 	kuid_t kuid;
 	kgid_t kgid;
 
-	kuid = mapped_fsuid(mnt_userns);
+	kuid = mapped_fsuid(mnt_userns, &init_user_ns);
 	if (!uid_valid(kuid))
 		return false;
-	kgid = mapped_fsgid(mnt_userns);
+	kgid = mapped_fsgid(mnt_userns, &init_user_ns);
 	if (!gid_valid(kgid))
 		return false;
 	return kuid_has_mapping(fs_userns, kuid) &&

include/linux/mnt_idmapping.h

@@ -196,6 +196,7 @@ static inline kgid_t mapped_kgid_user(struct user_namespace *mnt_userns,
 /**
  * mapped_fsuid - return caller's fsuid mapped up into a mnt_userns
  * @mnt_userns: the mount's idmapping
+ * @fs_userns: the filesystem's idmapping
  *
  * Use this helper to initialize a new vfs or filesystem object based on
  * the caller's fsuid. A common example is initializing the i_uid field of
@@ -205,14 +206,16 @@ static inline kgid_t mapped_kgid_user(struct user_namespace *mnt_userns,
  *
  * Return: the caller's current fsuid mapped up according to @mnt_userns.
  */
-static inline kuid_t mapped_fsuid(struct user_namespace *mnt_userns)
+static inline kuid_t mapped_fsuid(struct user_namespace *mnt_userns,
+				  struct user_namespace *fs_userns)
 {
-	return mapped_kuid_user(mnt_userns, &init_user_ns, current_fsuid());
+	return mapped_kuid_user(mnt_userns, fs_userns, current_fsuid());
 }
 
 /**
  * mapped_fsgid - return caller's fsgid mapped up into a mnt_userns
  * @mnt_userns: the mount's idmapping
+ * @fs_userns: the filesystem's idmapping
  *
  * Use this helper to initialize a new vfs or filesystem object based on
  * the caller's fsgid. A common example is initializing the i_gid field of
@@ -222,9 +225,10 @@ static inline kuid_t mapped_fsuid(struct user_namespace *mnt_userns)
  *
  * Return: the caller's current fsgid mapped up according to @mnt_userns.
  */
-static inline kgid_t mapped_fsgid(struct user_namespace *mnt_userns)
+static inline kgid_t mapped_fsgid(struct user_namespace *mnt_userns,
+				  struct user_namespace *fs_userns)
 {
-	return mapped_kgid_user(mnt_userns, &init_user_ns, current_fsgid());
+	return mapped_kgid_user(mnt_userns, fs_userns, current_fsgid());
 }
 
 #endif /* _LINUX_MNT_IDMAPPING_H */