xfs: don't return XFS_ATTR_PARENT attributes via listxattr

Parent pointers are internal filesystem metadata.  They're not intended
to be directly visible to userspace, so filter them out of
xfs_xattr_put_listent so that they don't appear in listxattr.
Signed-off-by: Allison Henderson <allison.henderson@oracle.com>
Inspired-by: Andrey Albershteyn <aalbersh@redhat.com>
Reviewed-by: Darrick J. Wong <djwong@kernel.org>
[djwong: change this to XFS_ATTR_PRIVATE_NSP_MASK per fsverity patchset]
Signed-off-by: Darrick J. Wong <djwong@kernel.org>
Reviewed-by: Christoph Hellwig <hch@lst.de>

fs/xfs/libxfs/xfs_da_format.h

@@ -726,6 +726,9 @@ struct xfs_attr3_leafblock {
 					 XFS_ATTR_SECURE | \
 					 XFS_ATTR_PARENT)
 
+/* Private attr namespaces not exposed to userspace */
+#define XFS_ATTR_PRIVATE_NSP_MASK	(XFS_ATTR_PARENT)
+
 #define XFS_ATTR_ONDISK_MASK	(XFS_ATTR_NSP_ONDISK_MASK | \
 				 XFS_ATTR_LOCAL | \
 				 XFS_ATTR_INCOMPLETE)

fs/xfs/xfs_xattr.c

@@ -229,6 +229,10 @@ xfs_xattr_put_listent(
 
 	ASSERT(context->count >= 0);
 
+	/* Don't expose private xattr namespaces. */
+	if (flags & XFS_ATTR_PRIVATE_NSP_MASK)
+		return;
+
 	if (flags & XFS_ATTR_ROOT) {
 #ifdef CONFIG_XFS_POSIX_ACL
 		if (namelen == SGI_ACL_FILE_SIZE &&