[PATCH 10/28] xfs: hide metadata inodes from everyone because they are special

Darrick J. Wong
2024-10-11T00:51:00Z

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>
---
fs/xfs/scrub/tempfile.c | 8 ++++++++
fs/xfs/xfs_iops.c | 15 ++++++++++++++-
2 files changed, 22 insertions(+), 1 deletion(-)

diff --git a/fs/xfs/scrub/tempfile.c b/fs/xfs/scrub/tempfile.c
index 177f922acfaf1b..3c5a1d77fefae9 100644
--- 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 ee79cf161312ca..33b51ea9bd210c 100644
--- 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_metadata_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