Re: [PATCH 2/4] xfs_repair: fix unaligned accesses

Dave Chinner
2015-10-11T22:26:45Z

On Thu, Oct 08, 2015 at 07:25:24PM -0500, Eric Sandeen wrote:
> This fixes some unaligned accesses spotted by libubsan in repair.
>
> Signed-off-by: Eric Sandeen <sandeen@redhat.com>
> ---
> repair/dinode.c | 19 +++++++++----------
> repair/prefetch.c | 4 ++--
> 2 files changed, 11 insertions(+), 12 deletions(-)
>
> diff --git a/repair/dinode.c b/repair/dinode.c
> index f78f907..44bbb8f 100644
> --- a/repair/dinode.c
> +++ b/repair/dinode.c
> @@ -960,13 +960,13 @@ _("bad numrecs 0 in inode %" PRIu64 " bmap btree root block\n"),
> * btree, we'd do it right here. For now, if there's a
> * problem, we'll bail out and presumably clear the inode.
> */
> - if (!verify_dfsbno(mp, be64_to_cpu(pp[i]))) {
> + if (!verify_dfsbno(mp, get_unaligned_be64(&pp[i]))) {

I don't understand - when are pointers in the BMBT not 64 bit
aligned? The buffers are allocated by memalign to be 64 bit aligned,
and all the internal BMBT structures are 64 bit aligned, too. i.e
the BMBT block header is 24/72 bytes in length (depending on CRCs),
the pointers are 64 bit, and the records are 128 bit.

So where's the unaligned access coming from?

Cheers,

Dave.
--
Dave Chinner
david@fromorbit.com