Re: [PATCH v2 1/5] xfs: check sb_agblocks and sb_agblklog when validating superblock

["Darrick J. Wong" <darrick.wong@oracle.com>]

On Tue, Jan 16, 2018 at 08:31:02AM +1100, Dave Chinner wrote:
> On Mon, Jan 15, 2018 at 12:03:13PM -0800, Darrick J. Wong wrote:
> > From: Darrick J. Wong <darrick.wong@oracle.com>
> > 
> > Currently, we don't check sb_agblocks or sb_agblklog when we validate
> > the superblock, which means that we can fuzz garbage values into those
> > values and the mount succeeds.  This leads to all sorts of UBSAN
> > warnings in xfs/350 since we can then coerce other parts of xfs into
> > shifting by ridiculously large values.
> > 
> > Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
> > ---
> > v2: simplify ag min/max size definitions
> > ---
> >  fs/xfs/libxfs/xfs_fs.h |    7 +++++++
> >  fs/xfs/libxfs/xfs_sb.c |    3 +++
> >  2 files changed, 10 insertions(+)
> > 
> > diff --git a/fs/xfs/libxfs/xfs_fs.h b/fs/xfs/libxfs/xfs_fs.h
> > index fc4386a..3ab1870 100644
> > --- a/fs/xfs/libxfs/xfs_fs.h
> > +++ b/fs/xfs/libxfs/xfs_fs.h
> > @@ -233,6 +233,13 @@ typedef struct xfs_fsop_resblks {
> >  #define XFS_MAX_LOG_BLOCKS	(1024 * 1024ULL)
> >  #define XFS_MIN_LOG_BYTES	(10 * 1024 * 1024ULL)
> >  
> > +/*
> > + * Limits on sb_agblocks/sb_agblklog -- mkfs won't format AGs smaller than
> > + * 16MB or larger than 1TB.
> > + */
> > +#define XFS_AG_MIN_BYTES	(1ULL << 24)	/* 16 MB */
> > +#define XFS_AG_MAX_BYTES	(1ULL << 40)	/* 1 TB */
> 
> Sure, but....
> > +
> >  /* keep the maximum size under 2^31 by a small amount */
> >  #define XFS_MAX_LOG_BYTES \
> >  	((2 * 1024 * 1024 * 1024ULL) - XFS_MIN_LOG_BYTES)
> > diff --git a/fs/xfs/libxfs/xfs_sb.c b/fs/xfs/libxfs/xfs_sb.c
> > index 08e44a0..bdb4f74 100644
> > --- a/fs/xfs/libxfs/xfs_sb.c
> > +++ b/fs/xfs/libxfs/xfs_sb.c
> > @@ -253,6 +253,9 @@ xfs_mount_validate_sb(
> >  	    sbp->sb_inodesize != (1 << sbp->sb_inodelog)		||
> >  	    sbp->sb_logsunit > XLOG_MAX_RECORD_BSIZE			||
> >  	    sbp->sb_inopblock != howmany(sbp->sb_blocksize,sbp->sb_inodesize) ||
> > +	    XFS_FSB_TO_B(mp, sbp->sb_agblocks) < XFS_AG_MIN_BYTES	||
> > +	    XFS_FSB_TO_B(mp, sbp->sb_agblocks) > XFS_AG_MAX_BYTES	||
> 
> .... this really needs to be checked against sb_dblocks /
> sb_agcount. i.e. check against current filesystem size and geometry,
> not against the theoretical maximum.

I think I prefer to check the theoretical maximum /and/ whether or not
ceil(dblocks/agblocks) == agcount, since we'd have to check agblocks != 0
prior to doing that anyway.

--D

> Cheers,
> 
> Dave.
> -- 
> Dave Chinner
> david@fromorbit.com
> --
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