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.
FWIW, I'm proposing a rudimentary bounds check to prevent this sort of
issue from even happening in the first place:
https://www.spinics.net/lists/linux-xfs/msg20592.html
>
> 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.
agreed, but again, I want to prevent the aforementioned use case where
corruption gets introduced.
>
> 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 and a clamp in _reinit_percpu_counters so
> that we never present ridiculous free counts to users?
>
> (Does any of this make sense with !haslazysbcount filesystems?)
>
> Bonus question: What about checking frextents/rextents?
Hrmm, perhaps. It should definitely be considered.
Thanks-
Bill
> --D
>
> > xfs_notice(mp, "SB sanity check failed");
> > return -EFSCORRUPTED;
> > }
> > --
> > 2.17.1
> >
> > --
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