xfs: convert flex-array declarations in xfs attr shortform objects

As of 6.5-rc1, UBSAN trips over the ondisk extended attribute shortform
definitions using an array length of 1 to pretend to be a flex array.
Kernel compilers have to support unbounded array declarations, so let's
correct this.
Signed-off-by: Darrick J. Wong <djwong@kernel.org>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Kees Cook <keescook@chromium.org>

fs/xfs/libxfs/xfs_da_format.h

@@ -591,7 +591,7 @@ struct xfs_attr_shortform {
 		uint8_t valuelen;	/* actual length of value (no NULL) */
 		uint8_t flags;	/* flags bits (see xfs_attr_leaf.h) */
 		uint8_t nameval[];	/* name & value bytes concatenated */
-	} list[1];			/* variable sized array */
+	} list[];			/* variable sized array */
 };
 
 typedef struct xfs_attr_leaf_map {	/* RLE map of free bytes */

fs/xfs/xfs_ondisk.h

@@ -89,6 +89,7 @@ xfs_check_ondisk_structs(void)
 	XFS_CHECK_OFFSET(xfs_attr_leaf_name_remote_t, namelen,	8);
 	XFS_CHECK_OFFSET(xfs_attr_leaf_name_remote_t, name,	9);
 	XFS_CHECK_STRUCT_SIZE(xfs_attr_leafblock_t,		32);
+	XFS_CHECK_STRUCT_SIZE(struct xfs_attr_shortform,	4);
 	XFS_CHECK_OFFSET(struct xfs_attr_shortform, hdr.totsize, 0);
 	XFS_CHECK_OFFSET(struct xfs_attr_shortform, hdr.count,	 2);
 	XFS_CHECK_OFFSET(struct xfs_attr_shortform, list[0].namelen,	4);