On Fri, Jul 13, 2018 at 09:41:53AM -0700, Darrick J. Wong wrote:
> On Fri, Jul 13, 2018 at 08:10:03AM -0500, Bill O'Donnell wrote:
> > Current sb verifier doesn't check bounds on sb_fdblocks and sb_ifree.
> > Add sanity checks for these parameters.
> >
> > Signed-off-by: Bill O'Donnell <billodo@xxxxxxxxxx>
> > ---
> > fs/xfs/libxfs/xfs_sb.c | 4 +++-
> > 1 file changed, 3 insertions(+), 1 deletion(-)
> >
> > diff --git a/fs/xfs/libxfs/xfs_sb.c b/fs/xfs/libxfs/xfs_sb.c
> > index 350119eeaecb..cdede769ab88 100644
> > --- a/fs/xfs/libxfs/xfs_sb.c
> > +++ b/fs/xfs/libxfs/xfs_sb.c
> > @@ -261,7 +261,9 @@ xfs_mount_validate_sb(
> > sbp->sb_dblocks == 0 ||
> > sbp->sb_dblocks > XFS_MAX_DBLOCKS(sbp) ||
> > sbp->sb_dblocks < XFS_MIN_DBLOCKS(sbp) ||
> > - sbp->sb_shared_vn != 0)) {
> > + sbp->sb_shared_vn != 0 ||
> > + sbp->sb_fdblocks > sbp->sb_dblocks ||
> > + sbp->sb_ifree > sbp->sb_icount)) {
>
> Hmm. On its face this seems reasonable for the superblock verifier, but
> then I started wondering, since these are /summary/ counters.
>
> If the free counts are off by this much, the admin won't be able to
> mount the fs, and xfs_repair is the only other tool that can fix the
> summary counts. However, if the log is dirty, the mount won't succeed
> to recover the fs, which is too bad since we can reinitialize the
> summary counts after log recovery. xfs_repair -L will be the only way
> out, which will wreak havoc on the filesystem from discarding the log
> contents.
Yup, that's why I said "catch this on /write/", not "always reject
bad counter values".
i.e. we should never be writing a bad value, but we most definitely
need to be able to mount the filesystem to reconstruct them.
> So, would it be preferable to split this into two parts? For example,
> have this as a corruption check in _sb_write_verify to prevent us from
> writing out garbage counters
yes.
> and a clamp in _reinit_percpu_counters so
> that we never present ridiculous free counts to users?
percpu_counter_{read,sum}_positive() should be used for anything that is
userspace facing. xfs_fs_counts() gets this right, but
xfs_fs_statfs() doesn't - it should use
percpu_counter_sum_positive().
> (Does any of this make sense with !haslazysbcount filesystems?)
Same thing - we can't verify the counters on read until after log
recovery as all the changes are journalled.
> Bonus question: What about checking frextents/rextents?
Same as !lazycount - all changes are journalled.
Cheers,
Dave.
--
Dave Chinner
david@xxxxxxxxxxxxx
--
To unsubscribe from this list: send the line "unsubscribe linux-xfs" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
