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

Brian Foster
2015-10-09T13:24:40Z

On Thu, Oct 08, 2015 at 07:25:24PM -0500, Eric Sandeen wrote:
> This fixes some unaligned accesses spotted by libubsan in repair.
>

Could we add a couple sentences about why this is a problem? I take it
unaligned accesses are "bad" on certain arches..?

> 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]))) {
> do_warn(_("bad bmap btree ptr 0x%llx in ino %" PRIu64 "\n"),
> - (unsigned long long) be64_to_cpu(pp[i]), lino);
> + get_unaligned_be64(&pp[i]), lino);
> return(1);
> }
>
> - if (scan_lbtree(be64_to_cpu(pp[i]), level, scan_bmapbt, type,
> + if (scan_lbtree(get_unaligned_be64(&pp[i]), level, scan_bmapbt, type,
> whichfork, lino, tot, nex, blkmapp, &cursor,
> 1, check_dups, magic, &xfs_bmbt_buf_ops))
> return(1);
> @@ -977,25 +977,24 @@ _("bad numrecs 0 in inode %" PRIu64 " bmap btree root block\n"),
> * blocks but the parent hasn't been updated
> */
> if (!check_dups && cursor.level[level-1].first_key !=
> - be64_to_cpu(pkey[i].br_startoff)) {
> + get_unaligned_be64(&pkey[i].br_startoff)) {
> if (!no_modify) {
> do_warn(
> _("correcting key in bmbt root (was %llu, now %" PRIu64") in inode "
> "%" PRIu64" %s fork\n"),
> - (unsigned long long)
> - be64_to_cpu(pkey[i].br_startoff),
> + get_unaligned_be64(&pkey[i].br_startoff),
> cursor.level[level-1].first_key,
> XFS_AGINO_TO_INO(mp, agno, ino),
> forkname);
> *dirty = 1;
> - pkey[i].br_startoff = cpu_to_be64(
> - cursor.level[level-1].first_key);
> + put_unaligned_be64(
> + cpu_to_be64(cursor.level[level-1].first_key),
> + &pkey[i].br_startoff);

I could be confused here... but if get_unaligned_be64() takes a be64 and
transforms to cpu order, shouldn't put_unaligned_be64() take a cpu order
parameter? Is this a double byte order swap?

Brian

> } else {
> do_warn(
> _("bad key in bmbt root (is %llu, would reset to %" PRIu64 ") in inode "
> "%" PRIu64 " %s fork\n"),
> - (unsigned long long)
> - be64_to_cpu(pkey[i].br_startoff),
> + get_unaligned_be64(&pkey[i].br_startoff),
> cursor.level[level-1].first_key,
> XFS_AGINO_TO_INO(mp, agno, ino),
> forkname);
> diff --git a/repair/prefetch.c b/repair/prefetch.c
> index 32ec55e..52238ca 100644
> --- a/repair/prefetch.c
> +++ b/repair/prefetch.c
> @@ -330,7 +330,7 @@ pf_scanfunc_bmap(
> pp = XFS_BMBT_PTR_ADDR(mp, block, 1, mp->m_bmap_dmxr[1]);
>
> for (i = 0; i < numrecs; i++) {
> - dbno = be64_to_cpu(pp[i]);
> + dbno = get_unaligned_be64(&pp[i]);
> if (!verify_dfsbno(mp, dbno))
> return 0;
> if (!pf_scan_lbtree(dbno, level, isadir, args, pf_scanfunc_bmap))
> @@ -372,7 +372,7 @@ pf_read_btinode(
> pp = XFS_BMDR_PTR_ADDR(dib, 1, xfs_bmdr_maxrecs(dsize, 0));
>
> for (i = 0; i < numrecs; i++) {
> - dbno = be64_to_cpu(pp[i]);
> + dbno = get_unaligned_be64(&pp[i]);
> if (!verify_dfsbno(mp, dbno))
> break;
> if (!pf_scan_lbtree(dbno, level, isadir, args, pf_scanfunc_bmap))
> --
> 1.7.1
>
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