[PATCH 1/4] xfs: hide private inodes from bulkstat and handle functions

Darrick J. Wong
2024-03-27T01:57:01Z

We're about to start adding functionality that uses internal inodes that
are private to XFS. What this means is that userspace should never be
able to access any information about these files, and should not be able
to open these files by handle.

To prevent users from ever finding the file or mis-interactions with the
security apparatus, set S_PRIVATE on the inode. Don't allow bulkstat,
open-by-handle, or linking of S_PRIVATE files into the directory tree.
This should keep private inodes actually private.

Signed-off-by: Darrick J. Wong <djwong@kernel.org>
---
fs/xfs/xfs_export.c | 2 +-
fs/xfs/xfs_iops.c | 3 +++
fs/xfs/xfs_itable.c | 8 ++++++++
3 files changed, 12 insertions(+), 1 deletion(-)

diff --git a/fs/xfs/xfs_export.c b/fs/xfs/xfs_export.c
index 7cd09c3a82cb5..4b03221351c0f 100644
--- a/fs/xfs/xfs_export.c
+++ b/fs/xfs/xfs_export.c
@@ -160,7 +160,7 @@ xfs_nfs_get_inode(
}
}

- if (VFS_I(ip)->i_generation != generation) {
+ if (VFS_I(ip)->i_generation != generation || IS_PRIVATE(VFS_I(ip))) {
xfs_irele(ip);
return ERR_PTR(-ESTALE);
}
diff --git a/fs/xfs/xfs_iops.c b/fs/xfs/xfs_iops.c
index 55ed2d1023d67..7f0c840f0fd2f 100644
--- a/fs/xfs/xfs_iops.c
+++ b/fs/xfs/xfs_iops.c
@@ -365,6 +365,9 @@ xfs_vn_link(
if (unlikely(error))
return error;

+ if (IS_PRIVATE(inode))
+ return -EPERM;
+
error = xfs_link(XFS_I(dir), XFS_I(inode), &name);
if (unlikely(error))
return error;
diff --git a/fs/xfs/xfs_itable.c b/fs/xfs/xfs_itable.c
index 95fc31b9f87d6..c0757ab994957 100644
--- a/fs/xfs/xfs_itable.c
+++ b/fs/xfs/xfs_itable.c
@@ -97,6 +97,14 @@ xfs_bulkstat_one_int(
vfsuid = i_uid_into_vfsuid(idmap, inode);
vfsgid = i_gid_into_vfsgid(idmap, inode);

+ /* If this is a private inode, don't leak its details to userspace. */
+ if (IS_PRIVATE(inode)) {
+ xfs_iunlock(ip, XFS_ILOCK_SHARED);
+ xfs_irele(ip);
+ error = -EINVAL;
+ goto out_advance;
+ }
+
/* xfs_iget returns the following without needing
* further change.
*/