xfs: hide metadata inodes from everyone because they are special

Metadata inodes are private files and therefore cannot be exposed to
userspace.  This means no bulkstat, no open-by-handle, no linking them
into the directory tree, and no feeding them to LSMs.  As such, we mark
them S_PRIVATE, which stops all that.

Signed-off-by: Darrick J. Wong <djwong@kernel.org>
Reviewed-by: Christoph Hellwig <hch@lst.de>

diff --git a/fs/xfs/scrub/tempfile.c b/fs/xfs/scrub/tempfile.c
index 177f922..3c5a1d7 100644 (file)
--- a/fs/xfs/scrub/tempfile.c
+++ b/fs/xfs/scrub/tempfile.c
@@ -844,6 +844,14 @@ xrep_is_tempfile(
        const struct xfs_inode  *ip)
 {
        const struct inode      *inode = &ip->i_vnode;
+       struct xfs_mount        *mp = ip->i_mount;
+
+       /*
+        * Files in the metadata directory tree also have S_PRIVATE set and
+        * IOP_XATTR unset, so we must distinguish them separately.
+        */
+       if (xfs_has_metadir(mp) && (ip->i_diflags2 & XFS_DIFLAG2_METADATA))
+               return false;
 
        if (IS_PRIVATE(inode) && !(inode->i_opflags & IOP_XATTR))
                return true;

diff --git a/fs/xfs/xfs_iops.c b/fs/xfs/xfs_iops.c
index ee79cf1..66a726a 100644 (file)
--- a/fs/xfs/xfs_iops.c
+++ b/fs/xfs/xfs_iops.c
@@ -42,7 +42,9 @@
  * held. For regular files, the lock order is the other way around - the
  * mmap_lock is taken during the page fault, and then we lock the ilock to do
  * block mapping. Hence we need a different class for the directory ilock so
- * that lockdep can tell them apart.
+ * that lockdep can tell them apart.  Directories in the metadata directory
+ * tree get a separate class so that lockdep reports will warn us if someone
+ * ever tries to lock regular directories after locking metadata directories.
  */
 static struct lock_class_key xfs_nondir_ilock_class;
 static struct lock_class_key xfs_dir_ilock_class;
@@ -1289,6 +1291,7 @@ xfs_setup_inode(
 {
        struct inode            *inode = &ip->i_vnode;
        gfp_t                   gfp_mask;
+       bool                    is_meta = xfs_is_internal_inode(ip);
 
        inode->i_ino = ip->i_ino;
        inode->i_state |= I_NEW;
@@ -1300,6 +1303,16 @@ xfs_setup_inode(
        i_size_write(inode, ip->i_disk_size);
        xfs_diflags_to_iflags(ip, true);
 
+       /*
+        * Mark our metadata files as private so that LSMs and the ACL code
+        * don't try to add their own metadata or reason about these files,
+        * and users cannot ever obtain file handles to them.
+        */
+       if (is_meta) {
+               inode->i_flags |= S_PRIVATE;
+               inode->i_opflags &= ~IOP_XATTR;
+       }
+
        if (S_ISDIR(inode->i_mode)) {
                /*
                 * We set the i_rwsem class here to avoid potential races with