xfs: convert flex-array declarations in struct xfs_attrlist*

xfs: convert flex-array declarations in struct xfs_attrlist*

Source kernel commit: 371baf5c9750a258fee21d0cb8c8d683bb057429

As of 6.5-rc1, UBSAN trips over the attrlist ioctl 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.  This
may cause friction with userspace header declarations, but suck is life.

================================================================================
UBSAN: array-index-out-of-bounds in fs/xfs/xfs_ioctl.c:345:18
index 1 is out of range for type '__s32 [1]'
Call Trace:
<TASK>
dump_stack_lvl+0x33/0x50
__ubsan_handle_out_of_bounds+0x9c/0xd0
xfs_ioc_attr_put_listent+0x413/0x420 [xfs 4a986a89a77bb77402ab8a87a37da369ef6a3f09]
xfs_attr_list_ilocked+0x170/0x850 [xfs 4a986a89a77bb77402ab8a87a37da369ef6a3f09]
xfs_attr_list+0xb7/0x120 [xfs 4a986a89a77bb77402ab8a87a37da369ef6a3f09]
xfs_ioc_attr_list+0x13b/0x2e0 [xfs 4a986a89a77bb77402ab8a87a37da369ef6a3f09]
xfs_attrlist_by_handle+0xab/0x120 [xfs 4a986a89a77bb77402ab8a87a37da369ef6a3f09]
xfs_file_ioctl+0x1ff/0x15e0 [xfs 4a986a89a77bb77402ab8a87a37da369ef6a3f09]
vfs_ioctl+0x1f/0x60

The kernel and xfsprogs code that uses these structures will not have
problems, but the long tail of external user programs might.

Signed-off-by: Darrick J. Wong <djwong@kernel.org>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Carlos Maiolino <cem@kernel.org>