Merge tag 'fs.idmapped.helpers.v5.13' of git://git.kernel.org/pub/scm/linux/kernel/git/brauner/linux

Pull fs mapping helper updates from Christian Brauner:
 "This adds kernel-doc to all new idmapping helpers and improves their
  naming which was triggered by a discussion with some fs developers.
  Some of the names are based on suggestions by Vivek and Al.

  Also remove the open-coded permission checking in a few places with
  simple helpers. Overall this should lead to more clarity and make it
  easier to maintain"

* tag 'fs.idmapped.helpers.v5.13' of git://git.kernel.org/pub/scm/linux/kernel/git/brauner/linux:
  fs: introduce two inode i_{u,g}id initialization helpers
  fs: introduce fsuidgid_has_mapping() helper
  fs: document and rename fsid helpers
  fs: document mapping helpers

6 files changed, 135 insertions, 20 deletions

diff --git a/fs/ext4/ialloc.c b/fs/ext4/ialloc.c
index 633ae7becd61..755a68bb7e22 100644
--- a/fs/ext4/ialloc.c
+++ b/fs/ext4/ialloc.c
@@ -970,7 +970,7 @@ struct inode *__ext4_new_inode(struct user_namespace *mnt_userns,
 		i_gid_write(inode, owner[1]);
 	} else if (test_opt(sb, GRPID)) {
 		inode->i_mode = mode;
-		inode->i_uid = fsuid_into_mnt(mnt_userns);
+		inode_fsuid_set(inode, mnt_userns);
 		inode->i_gid = dir->i_gid;
 	} else
 		inode_init_owner(mnt_userns, inode, dir, mode);
diff --git a/fs/inode.c b/fs/inode.c
index ae526fd9c0a4..9e192bea0630 100644
--- a/fs/inode.c
+++ b/fs/inode.c
@@ -2147,7 +2147,7 @@ EXPORT_SYMBOL(init_special_inode);
 void inode_init_owner(struct user_namespace *mnt_userns, struct inode *inode,
 		      const struct inode *dir, umode_t mode)
 {
-	inode->i_uid = fsuid_into_mnt(mnt_userns);
+	inode_fsuid_set(inode, mnt_userns);
 	if (dir && dir->i_mode & S_ISGID) {
 		inode->i_gid = dir->i_gid;
 
@@ -2159,7 +2159,7 @@ void inode_init_owner(struct user_namespace *mnt_userns, struct inode *inode,
 			 !capable_wrt_inode_uidgid(mnt_userns, dir, CAP_FSETID))
 			mode &= ~S_ISGID;
 	} else
-		inode->i_gid = fsgid_into_mnt(mnt_userns);
+		inode_fsgid_set(inode, mnt_userns);
 	inode->i_mode = mode;
 }
 EXPORT_SYMBOL(inode_init_owner);
diff --git a/fs/namei.c b/fs/namei.c
index 0fa000ad7e9b..79b0ff9b151e 100644
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -2824,16 +2824,14 @@ static int may_delete(struct user_namespace *mnt_userns, struct inode *dir,
 static inline int may_create(struct user_namespace *mnt_userns,
 			     struct inode *dir, struct dentry *child)
 {
-	struct user_namespace *s_user_ns;
 	audit_inode_child(dir, child, AUDIT_TYPE_CHILD_CREATE);
 	if (child->d_inode)
 		return -EEXIST;
 	if (IS_DEADDIR(dir))
 		return -ENOENT;
-	s_user_ns = dir->i_sb->s_user_ns;
-	if (!kuid_has_mapping(s_user_ns, fsuid_into_mnt(mnt_userns)) ||
-	    !kgid_has_mapping(s_user_ns, fsgid_into_mnt(mnt_userns)))
+	if (!fsuidgid_has_mapping(dir->i_sb, mnt_userns))
 		return -EOVERFLOW;
+
 	return inode_permission(mnt_userns, dir, MAY_WRITE | MAY_EXEC);
 }
 
@@ -3035,14 +3033,11 @@ static int may_o_create(struct user_namespace *mnt_userns,
 			const struct path *dir, struct dentry *dentry,
 			umode_t mode)
 {
-	struct user_namespace *s_user_ns;
 	int error = security_path_mknod(dir, dentry, mode, 0);
 	if (error)
 		return error;
 
-	s_user_ns = dir->dentry->d_sb->s_user_ns;
-	if (!kuid_has_mapping(s_user_ns, fsuid_into_mnt(mnt_userns)) ||
-	    !kgid_has_mapping(s_user_ns, fsgid_into_mnt(mnt_userns)))
+	if (!fsuidgid_has_mapping(dir->dentry->d_sb, mnt_userns))
 		return -EOVERFLOW;
 
 	error = inode_permission(mnt_userns, dir->dentry->d_inode,
diff --git a/fs/xfs/xfs_inode.c b/fs/xfs/xfs_inode.c
index f93370bd7b1e..2a8bdf33e6c4 100644
--- a/fs/xfs/xfs_inode.c
+++ b/fs/xfs/xfs_inode.c
@@ -812,7 +812,7 @@ xfs_init_new_inode(
 
 	if (dir && !(dir->i_mode & S_ISGID) &&
 	    (mp->m_flags & XFS_MOUNT_GRPID)) {
-		inode->i_uid = fsuid_into_mnt(mnt_userns);
+		inode_fsuid_set(inode, mnt_userns);
 		inode->i_gid = dir->i_gid;
 		inode->i_mode = mode;
 	} else {
@@ -1007,8 +1007,8 @@ xfs_create(
 	/*
 	 * Make sure that we have allocated dquot(s) on disk.
 	 */
-	error = xfs_qm_vop_dqalloc(dp, fsuid_into_mnt(mnt_userns),
-			fsgid_into_mnt(mnt_userns), prid,
+	error = xfs_qm_vop_dqalloc(dp, mapped_fsuid(mnt_userns),
+			mapped_fsgid(mnt_userns), prid,
 			XFS_QMOPT_QUOTALL | XFS_QMOPT_INHERIT,
 			&udqp, &gdqp, &pdqp);
 	if (error)
@@ -1158,8 +1158,8 @@ xfs_create_tmpfile(
 	/*
 	 * Make sure that we have allocated dquot(s) on disk.
 	 */
-	error = xfs_qm_vop_dqalloc(dp, fsuid_into_mnt(mnt_userns),
-			fsgid_into_mnt(mnt_userns), prid,
+	error = xfs_qm_vop_dqalloc(dp, mapped_fsuid(mnt_userns),
+			mapped_fsgid(mnt_userns), prid,
 			XFS_QMOPT_QUOTALL | XFS_QMOPT_INHERIT,
 			&udqp, &gdqp, &pdqp);
 	if (error)
diff --git a/fs/xfs/xfs_symlink.c b/fs/xfs/xfs_symlink.c
index 7f368b10ded1..63edb4dbed4a 100644
--- a/fs/xfs/xfs_symlink.c
+++ b/fs/xfs/xfs_symlink.c
@@ -182,8 +182,8 @@ xfs_symlink(
 	/*
 	 * Make sure that we have allocated dquot(s) on disk.
 	 */
-	error = xfs_qm_vop_dqalloc(dp, fsuid_into_mnt(mnt_userns),
-			fsgid_into_mnt(mnt_userns), prid,
+	error = xfs_qm_vop_dqalloc(dp, mapped_fsuid(mnt_userns),
+			mapped_fsgid(mnt_userns), prid,
 			XFS_QMOPT_QUOTALL | XFS_QMOPT_INHERIT,
 			&udqp, &gdqp, &pdqp);
 	if (error)
diff --git a/include/linux/fs.h b/include/linux/fs.h
index 2e80a1e79fb5..5ac7bad3f0de 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -1575,52 +1575,172 @@ static inline void i_gid_write(struct inode *inode, gid_t gid)
 	inode->i_gid = make_kgid(inode->i_sb->s_user_ns, gid);
 }
 
+/**
+ * kuid_into_mnt - map a kuid down into a mnt_userns
+ * @mnt_userns: user namespace of the relevant mount
+ * @kuid: kuid to be mapped
+ *
+ * Return: @kuid mapped according to @mnt_userns.
+ * If @kuid has no mapping INVALID_UID is returned.
+ */
 static inline kuid_t kuid_into_mnt(struct user_namespace *mnt_userns,
 				   kuid_t kuid)
 {
 	return make_kuid(mnt_userns, __kuid_val(kuid));
 }
 
+/**
+ * kgid_into_mnt - map a kgid down into a mnt_userns
+ * @mnt_userns: user namespace of the relevant mount
+ * @kgid: kgid to be mapped
+ *
+ * Return: @kgid mapped according to @mnt_userns.
+ * If @kgid has no mapping INVALID_GID is returned.
+ */
 static inline kgid_t kgid_into_mnt(struct user_namespace *mnt_userns,
 				   kgid_t kgid)
 {
 	return make_kgid(mnt_userns, __kgid_val(kgid));
 }
 
+/**
+ * i_uid_into_mnt - map an inode's i_uid down into a mnt_userns
+ * @mnt_userns: user namespace of the mount the inode was found from
+ * @inode: inode to map
+ *
+ * Return: the inode's i_uid mapped down according to @mnt_userns.
+ * If the inode's i_uid has no mapping INVALID_UID is returned.
+ */
 static inline kuid_t i_uid_into_mnt(struct user_namespace *mnt_userns,
 				    const struct inode *inode)
 {
 	return kuid_into_mnt(mnt_userns, inode->i_uid);
 }
 
+/**
+ * i_gid_into_mnt - map an inode's i_gid down into a mnt_userns
+ * @mnt_userns: user namespace of the mount the inode was found from
+ * @inode: inode to map
+ *
+ * Return: the inode's i_gid mapped down according to @mnt_userns.
+ * If the inode's i_gid has no mapping INVALID_GID is returned.
+ */
 static inline kgid_t i_gid_into_mnt(struct user_namespace *mnt_userns,
 				    const struct inode *inode)
 {
 	return kgid_into_mnt(mnt_userns, inode->i_gid);
 }
 
+/**
+ * kuid_from_mnt - map a kuid up into a mnt_userns
+ * @mnt_userns: user namespace of the relevant mount
+ * @kuid: kuid to be mapped
+ *
+ * Return: @kuid mapped up according to @mnt_userns.
+ * If @kuid has no mapping INVALID_UID is returned.
+ */
 static inline kuid_t kuid_from_mnt(struct user_namespace *mnt_userns,
 				   kuid_t kuid)
 {
 	return KUIDT_INIT(from_kuid(mnt_userns, kuid));
 }
 
+/**
+ * kgid_from_mnt - map a kgid up into a mnt_userns
+ * @mnt_userns: user namespace of the relevant mount
+ * @kgid: kgid to be mapped
+ *
+ * Return: @kgid mapped up according to @mnt_userns.
+ * If @kgid has no mapping INVALID_GID is returned.
+ */
 static inline kgid_t kgid_from_mnt(struct user_namespace *mnt_userns,
 				   kgid_t kgid)
 {
 	return KGIDT_INIT(from_kgid(mnt_userns, kgid));
 }
 
-static inline kuid_t fsuid_into_mnt(struct user_namespace *mnt_userns)
+/**
+ * mapped_fsuid - return caller's fsuid mapped up into a mnt_userns
+ * @mnt_userns: user namespace of the relevant mount
+ *
+ * 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
+ * a newly allocated inode triggered by a creation event such as mkdir or
+ * 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.
+ */
+static inline kuid_t mapped_fsuid(struct user_namespace *mnt_userns)
 {
 	return kuid_from_mnt(mnt_userns, current_fsuid());
 }
 
-static inline kgid_t fsgid_into_mnt(struct user_namespace *mnt_userns)
+/**
+ * mapped_fsgid - return caller's fsgid mapped up into a mnt_userns
+ * @mnt_userns: user namespace of the relevant mount
+ *
+ * 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
+ * a newly allocated inode triggered by a creation event such as mkdir or
+ * 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.
+ */
+static inline kgid_t mapped_fsgid(struct user_namespace *mnt_userns)
 {
 	return kgid_from_mnt(mnt_userns, current_fsgid());
 }
 
+/**
+ * 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
+ *
+ * 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.
+ */
+static inline void inode_fsuid_set(struct inode *inode,
+				   struct user_namespace *mnt_userns)
+{
+	inode->i_uid = mapped_fsuid(mnt_userns);
+}
+
+/**
+ * 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
+ *
+ * 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.
+ */
+static inline void inode_fsgid_set(struct inode *inode,
+				   struct user_namespace *mnt_userns)
+{
+	inode->i_gid = mapped_fsgid(mnt_userns);
+}
+
+/**
+ * fsuidgid_has_mapping() - check whether caller's fsuid/fsgid is mapped
+ * @sb: the superblock we want a mapping in
+ * @mnt_userns: user namespace of the relevant mount
+ *
+ * Check whether the caller's fsuid and fsgid have a valid mapping in the
+ * s_user_ns of the superblock @sb. If the caller is on an idmapped mount map
+ * the caller's fsuid and fsgid according to the @mnt_userns first.
+ *
+ * Return: true if fsuid and fsgid is mapped, false if not.
+ */
+static inline bool fsuidgid_has_mapping(struct super_block *sb,
+					struct user_namespace *mnt_userns)
+{
+	struct user_namespace *s_user_ns = sb->s_user_ns;
+
+	return kuid_has_mapping(s_user_ns, mapped_fsuid(mnt_userns)) &&
+	       kgid_has_mapping(s_user_ns, mapped_fsgid(mnt_userns));
+}
+
 extern struct timespec64 current_time(struct inode *inode);
 
 /*