fs: port acl 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 <dchinner@redhat.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Christian Brauner (Microsoft) <brauner@kernel.org>

1 files changed, 17 insertions, 16 deletions

diff --git a/fs/namei.c b/fs/namei.c
index a88017266ee5..637f8bee7132 100644
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -273,7 +273,7 @@ void putname(struct filename *name)
 
 /**
  * check_acl - perform ACL permission checking
- * @mnt_userns:	user namespace of the mount the inode was found from
+ * @idmap:	idmap of the mount the inode was found from
  * @inode:	inode to check permissions on
  * @mask:	right to check for (%MAY_READ, %MAY_WRITE, %MAY_EXEC ...)
  *
@@ -281,13 +281,13 @@ void putname(struct filename *name)
  * retrieve POSIX acls it needs to know whether it is called from a blocking or
  * non-blocking context and thus cares about the MAY_NOT_BLOCK bit.
  *
- * If the inode has been found through an idmapped mount the user namespace of
- * the vfsmount must be passed through @mnt_userns. This function will then take
- * care to map the inode according to @mnt_userns before checking permissions.
+ * If the inode has been found through an idmapped mount the idmap of
+ * the vfsmount must be passed through @idmap. This function will then take
+ * care to map the inode according to @idmap before checking permissions.
  * On non-idmapped mounts or if permission checking is to be performed on the
- * raw inode simply passs init_user_ns.
+ * raw inode simply passs @nop_mnt_idmap.
  */
-static int check_acl(struct user_namespace *mnt_userns,
+static int check_acl(struct mnt_idmap *idmap,
 		     struct inode *inode, int mask)
 {
 #ifdef CONFIG_FS_POSIX_ACL
@@ -300,14 +300,14 @@ static int check_acl(struct user_namespace *mnt_userns,
 		/* no ->get_inode_acl() calls in RCU mode... */
 		if (is_uncached_acl(acl))
 			return -ECHILD;
-	        return posix_acl_permission(mnt_userns, inode, acl, mask);
+	        return posix_acl_permission(idmap, inode, acl, mask);
 	}
 
 	acl = get_inode_acl(inode, ACL_TYPE_ACCESS);
 	if (IS_ERR(acl))
 		return PTR_ERR(acl);
 	if (acl) {
-	        int error = posix_acl_permission(mnt_userns, inode, acl, mask);
+	        int error = posix_acl_permission(idmap, inode, acl, mask);
 	        posix_acl_release(acl);
 	        return error;
 	}
@@ -318,7 +318,7 @@ static int check_acl(struct user_namespace *mnt_userns,
 
 /**
  * acl_permission_check - perform basic UNIX permission checking
- * @mnt_userns:	user namespace of the mount the inode was found from
+ * @idmap:	idmap of the mount the inode was found from
  * @inode:	inode to check permissions on
  * @mask:	right to check for (%MAY_READ, %MAY_WRITE, %MAY_EXEC ...)
  *
@@ -326,15 +326,16 @@ static int check_acl(struct user_namespace *mnt_userns,
  * function may retrieve POSIX acls it needs to know whether it is called from a
  * blocking or non-blocking context and thus cares about the MAY_NOT_BLOCK bit.
  *
- * If the inode has been found through an idmapped mount the user namespace of
- * the vfsmount must be passed through @mnt_userns. This function will then take
- * care to map the inode according to @mnt_userns before checking permissions.
+ * If the inode has been found through an idmapped mount the idmap of
+ * the vfsmount must be passed through @idmap. This function will then take
+ * care to map the inode according to @idmap before checking permissions.
  * On non-idmapped mounts or if permission checking is to be performed on the
- * raw inode simply passs init_user_ns.
+ * raw inode simply passs @nop_mnt_idmap.
  */
-static int acl_permission_check(struct user_namespace *mnt_userns,
+static int acl_permission_check(struct mnt_idmap *idmap,
 				struct inode *inode, int mask)
 {
+	struct user_namespace *mnt_userns = mnt_idmap_owner(idmap);
 	unsigned int mode = inode->i_mode;
 	vfsuid_t vfsuid;
 
@@ -348,7 +349,7 @@ static int acl_permission_check(struct user_namespace *mnt_userns,
 
 	/* Do we have ACL's? */
 	if (IS_POSIXACL(inode) && (mode & S_IRWXG)) {
-		int error = check_acl(mnt_userns, inode, mask);
+		int error = check_acl(idmap, inode, mask);
 		if (error != -EAGAIN)
 			return error;
 	}
@@ -402,7 +403,7 @@ int generic_permission(struct mnt_idmap *idmap, struct inode *inode,
 	/*
 	 * Do the basic permission checks.
 	 */
-	ret = acl_permission_check(mnt_userns, inode, mask);
+	ret = acl_permission_check(idmap, inode, mask);
 	if (ret != -EACCES)
 		return ret;