Re: [PATCH v2] libxfs: add more bounds checking to sb sanity checks

[Bill O'Donnell <billodo@redhat.com>]

On Tue, Jul 17, 2018 at 12:17:14PM -0500, Bill O'Donnell wrote:
> On Tue, Jul 17, 2018 at 10:06:54AM -0700, Darrick J. Wong wrote:
> > On Mon, Jul 16, 2018 at 02:26:55PM -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@redhat.com>
> > > ---
> > > v2: make extra sanity checks exclusive to writes (allow read)
> > > 
> > >  fs/xfs/libxfs/xfs_sb.c | 22 +++++++++++++++++-----
> > >  1 file changed, 17 insertions(+), 5 deletions(-)
> > > 
> > > diff --git a/fs/xfs/libxfs/xfs_sb.c b/fs/xfs/libxfs/xfs_sb.c
> > > index 350119eeaecb..6a98ec68e8ad 100644
> > > --- a/fs/xfs/libxfs/xfs_sb.c
> > > +++ b/fs/xfs/libxfs/xfs_sb.c
> > > @@ -104,7 +104,8 @@ xfs_mount_validate_sb(
> > >  	xfs_mount_t	*mp,
> > >  	xfs_sb_t	*sbp,
> > >  	bool		check_inprogress,
> > > -	bool		check_version)
> > > +	bool		check_version,
> > > +	bool		write_flag)
> > 
> > I notice that check_version and write_flag are always xor -- either
> > we're reading the sb and set check_version, or we're writing the sb and
> > set write_flag.  Perhaps we can combine these two as write_flag?
> > 
> > if (check_version)
> > 	check version stuff...
> > 
> > becomes:
> > 
> > if (!write_flag)
> > 	check version stuff...
> > 
> > and we only have to pass around one flag.
> 
> I suppose that makes sense, but my notion is that 2 unique flags
> is preferable for clarity and mutual exclusiveness for anyone doing
> subsequent patches.

I'm all for simplifying and saving stack space, but is it ok
to turn a single purpose flag into a dual purpose one?

> 
> > 
> > >  {
> > >  	uint32_t	agcount = 0;
> > >  	uint32_t	rem;
> > > @@ -266,6 +267,15 @@ xfs_mount_validate_sb(
> > >  		return -EFSCORRUPTED;
> > >  	}
> > >  
> > > +	/* Additional sb sanity checks for writes */
> > > +	if (write_flag) {
> > > +		if (sbp->sb_fdblocks > sbp->sb_dblocks ||
> > > +		    sbp->sb_ifree > sbp->sb_icount) {
> > 
> > Hmm, we still need something that will detect this on read and set a
> > flag to force recalculation of the summary counters... though since a
> > patch to implement that flag is sitting in my tree I'll take care of
> > that part separately.
> 
> That sounds good, thanks!
> -Bill
> 
> > 
> > --D
> > 
> > > +			    xfs_notice(mp, "SB sanity check failed");
> > > +			    return -EFSCORRUPTED;
> > > +		}
> > > +	}
> > > +
> > >  	if (sbp->sb_unit) {
> > >  		if (!xfs_sb_version_hasdalign(sbp) ||
> > >  		    sbp->sb_unit > sbp->sb_width ||
> > > @@ -599,7 +609,9 @@ xfs_sb_to_disk(
> > >  static int
> > >  xfs_sb_verify(
> > >  	struct xfs_buf	*bp,
> > > -	bool		check_version)
> > > +	bool		check_version,
> > > +	bool		write_flag)
> > > +
> > >  {
> > >  	struct xfs_mount *mp = bp->b_target->bt_mount;
> > >  	struct xfs_sb	sb;
> > > @@ -616,7 +628,7 @@ xfs_sb_verify(
> > >  	 */
> > >  	return xfs_mount_validate_sb(mp, &sb,
> > >  				     bp->b_maps[0].bm_bn == XFS_SB_DADDR,
> > > -				     check_version);
> > > +				     check_version, write_flag);
> > >  }
> > >  
> > >  /*
> > > @@ -657,7 +669,7 @@ xfs_sb_read_verify(
> > >  			}
> > >  		}
> > >  	}
> > > -	error = xfs_sb_verify(bp, true);
> > > +	error = xfs_sb_verify(bp, true, false);
> > >  
> > >  out_error:
> > >  	if (error == -EFSCORRUPTED || error == -EFSBADCRC)
> > > @@ -695,7 +707,7 @@ xfs_sb_write_verify(
> > >  	struct xfs_buf_log_item	*bip = bp->b_log_item;
> > >  	int			error;
> > >  
> > > -	error = xfs_sb_verify(bp, false);
> > > +	error = xfs_sb_verify(bp, false, true);
> > >  	if (error) {
> > >  		xfs_verifier_error(bp, error, __this_address);
> > >  		return;
> > > -- 
> > > 2.17.1
> > > 
> > > --
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