On Tue, Jan 24, 2017 at 09:09:01PM -0600, Eric Sandeen wrote:
> Before we get into libxfs_initialize_perag and try to blindly
> allocate a perag struct for every (possibly corrupted number of)
> AGs, see if we can read the last one. If not, assume it's corrupt,
> and load only the first AG.
>
> Do this only for an arbitrarily high-ish agcount, so that normal-ish
> geometry on a possibly truncated file or device will still do
> its best to make all readable AGs available.
>
> Signed-off-by: Eric Sandeen <sandeen@xxxxxxxxxx>
> ---
Huh, what happened to v1-6? :)
> v7: blow it all up
> v8: use bare libxfs_readbuf so verifiers don't matter,
> "ours goes to 1 million!"
>
> diff --git a/libxfs/init.c b/libxfs/init.c
> index a08575a..a14aa17 100644
> --- a/libxfs/init.c
> +++ b/libxfs/init.c
> @@ -817,6 +817,29 @@ libxfs_mount(
> return NULL;
> }
>
> + /*
> + * libxfs_initialize_perag will allocate a perag structure for each ag.
> + * If agcount is corrupted and insanely high, this will OOM the box.
> + * If the agount seems (arbitrarily) high, try to read what would be
> + * the last AG, and if that fails for a relatively high agcount, just
> + * read the first one and let the user know to check the geometry.
> + */
> + if (sbp->sb_agcount > 1000000) {
> + bp = libxfs_readbuf(mp->m_dev,
> + XFS_AG_DADDR(mp, sbp->sb_agcount - 1, 0), 1,
> + !(flags & LIBXFS_MOUNT_DEBUGGER), NULL);
> + if (bp->b_error) {
> + fprintf(stderr, _("%s: read of AG %d failed\n"),
> + progname, sbp->sb_agcount);
AG counts are unsigned.
# xfs_db -x -c 'sb 0' -c 'fuzz -d agcount random' /dev/sdf
Allowing fuzz of corrupted data with good CRC
agcount = 3298133433
# xfs_db /dev/sdf
xfs_db: error - read only 0 of 512 bytes
xfs_db: read of AG -996833863 failed
xfs_db: limiting reads to AG 0
Assuming it passes testing, fix the two things, slap on a:
Reviewed-by: Darrick J. Wong <darrick.wong@xxxxxxxxxx>
and let's call it done.
--D
> + if (!(flags & LIBXFS_MOUNT_DEBUGGER))
> + return NULL;
> + fprintf(stderr, _("%s: limiting reads to AG 0\n"),
> + progname);
> + sbp->sb_agcount = 1;
> + }
> + libxfs_putbuf(bp);
> + }
> +
> error = libxfs_initialize_perag(mp, sbp->sb_agcount, &mp->m_maxagi);
> if (error) {
> fprintf(stderr, _("%s: perag init failed\n"),
>
> --
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