Re: [PATCH 2/2] xfs: More robust inode extent count validation

[Dave Chinner <david@fromorbit.com>]

On Mon, Jun 18, 2018 at 09:57:25PM -0700, Darrick J. Wong wrote:
> On Tue, Jun 19, 2018 at 12:41:28PM +1000, Dave Chinner wrote:
> > From: Dave Chinner <dchinner@redhat.com>
> > 
> > When the inode is in extent format, it can't have more extents that
> > fit in the inode fork. We don't currenty check this, and so this
> > corruption goes unnoticed by the inode verifiers. This can lead to
> > crashes operating on invalid in-memory structures.
> > 
> > Attempts to access such a inode will now error out in the verifier
> > rather than allowing modification operations to proceed.
> > 
> > Reported-by: Wen Xu <wen.xu@gatech.edu>
> > Signed-off-by: Dave Chinner <dchinner@redhat.com>
> > ---
> >  fs/xfs/libxfs/xfs_format.h    |  3 ++
> >  fs/xfs/libxfs/xfs_inode_buf.c | 74 +++++++++++++++++++++--------------
> >  2 files changed, 48 insertions(+), 29 deletions(-)
> > 
> > diff --git a/fs/xfs/libxfs/xfs_format.h b/fs/xfs/libxfs/xfs_format.h
> > index 1c5a8aaf2bfc..1cb298fec274 100644
> > --- a/fs/xfs/libxfs/xfs_format.h
> > +++ b/fs/xfs/libxfs/xfs_format.h
> > @@ -962,6 +962,9 @@ typedef enum xfs_dinode_fmt {
> >  		XFS_DFORK_DSIZE(dip, mp) : \
> >  		XFS_DFORK_ASIZE(dip, mp))
> >  
> > +#define XFS_DFORK_MAXEXT(dip, mp, w) \
> > +	(XFS_DFORK_SIZE(dip, mp, w) / sizeof(xfs_bmbt_rec_t))
> > +
> >  /*
> >   * Return pointers to the data or attribute forks.
> >   */
> > diff --git a/fs/xfs/libxfs/xfs_inode_buf.c b/fs/xfs/libxfs/xfs_inode_buf.c
> > index d38d724534c4..a41b6e5519e0 100644
> > --- a/fs/xfs/libxfs/xfs_inode_buf.c
> > +++ b/fs/xfs/libxfs/xfs_inode_buf.c
> > @@ -374,6 +374,45 @@ xfs_log_dinode_to_disk(
> >  	}
> >  }
> >  
> > +static xfs_failaddr_t
> > +xfs_dinode_verify_fork(
> > +	struct xfs_dinode	*dip,
> > +	struct xfs_mount	*mp,
> > +	int			whichfork)
> > +{
> > +	uint32_t		di_nextents = XFS_DFORK_NEXTENTS(dip, whichfork);
> > +
> > +	switch (XFS_DFORK_FORMAT(dip, whichfork)) {
> > +	case XFS_DINODE_FMT_LOCAL:
> > +		/*
> > +		 * no local regular files yet
> > +		 */
> > +		if (whichfork == XFS_DATA_FORK) {
> > +			if (S_ISREG(be16_to_cpu(dip->di_mode)))
> > +				return __this_address;
> > +			if (be64_to_cpu(dip->di_size) >
> > +					XFS_DFORK_SIZE(dip, mp, whichfork))
> > +				return __this_address;
> > +		}
> > +		if (di_nextents)
> > +			return __this_address;
> > +		/* fall through */
> 
> We could break here too, right?  There's no point in further checks of
> di_nextents for local format forks.
> 
> > +	case XFS_DINODE_FMT_EXTENTS:
> > +		if (di_nextents > XFS_DFORK_MAXEXT(dip, mp, whichfork))
> > +			return __this_address;
> 
> Are we supposed to break here?

They all fall through like they used to, but they could break, too.
The behaviour will be the same now.

Cheers,

Dave.
-- 
Dave Chinner
david@fromorbit.com