Re: [PATCH v2 4/5] xfs_db: sanitize geometry on load

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

On Thu, Jan 12, 2017 at 05:20:26PM -0600, Eric Sandeen wrote:
> On 1/12/17 2:41 PM, Darrick J. Wong wrote:
> > xfs_db doesn't check the filesystem geometry when it's mounting, which
> > means that garbage agcount values can cause OOMs when we try to allocate
> > all the per-AG incore metadata.  If we see geometry that looks
> > suspicious, try to derive the actual AG geometry to avoid crashing the
> > system.  This should help with xfs/1301 fuzzing.
> > 
> > Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
> > ---
> > v2: Only modify sb_ag{blocks,count} if they seem insane -- use local
> > variables to avoid screwing up the rest of the metadata.
> 
> Ok, I like this a bit better.  More comments, though.  Sorry, will
> try to do a better full review in future to avoid the iteration :(
> Below ...
> 
> > ---
> >  db/init.c |   97 +++++++++++++++++++++++++++++++++++++++++++++++++++++++------
> >  1 file changed, 87 insertions(+), 10 deletions(-)
> > 
> > diff --git a/db/init.c b/db/init.c
> > index ec1e274..db133d7 100644
> > --- a/db/init.c
> > +++ b/db/init.c
> > @@ -51,13 +51,96 @@ usage(void)
> >  	exit(1);
> >  }
> >  
> > +/* Try to load an AG's superblock, no verifiers. */
> 
> /* ... for the given agno ... */
> 
> > +static bool
> > +load_sb(
> > +	struct xfs_mount	*mp,
> > +	xfs_agnumber_t		agno,
> > +	struct xfs_sb		*sbp)
> > +{
> > +	struct xfs_buf		*bp;
> > +
> > +	bp = libxfs_readbuf(mp->m_ddev_targp,
> > +			    XFS_AG_DADDR(mp, agno, XFS_SB_DADDR),
> > +			    1 << (XFS_MAX_SECTORSIZE_LOG - BBSHIFT), 0, NULL);
> > +
> > +	if (!bp || bp->b_error)
> > +		return false;
> > +
> > +	/* copy SB from buffer to in-core, converting architecture as we go */
> > +	libxfs_sb_from_disk(sbp, XFS_BUF_TO_SBP(bp));
> > +	libxfs_putbuf(bp);
> > +	libxfs_purgebuf(bp);
> > +
> > +	return true;
> > +}
> > +
> > +/* If the geometry doesn't look sane, try to figure out the real geometry. */
> > +static void
> > +sanitize_geometry(
> Probably now:
> 
> +/*
> + * If the agcount doesn't look sane, try to figure out the real agcount.
> + * A wildly too-large agcount may OOM in libxfs_initialize_perag
> + */
> +static void
> +sanitize_agcount(
> 
> > +	struct xfs_mount	*mp,
> > +	struct xfs_sb		*sbp)
> > +{
> > +	struct xfs_sb		sb;
> > +	unsigned int		blocklog;
> > +	unsigned int		blocksize;
> > +	unsigned int		agblocks;
> > +	unsigned long long	dblocks;
> > +
> > +	/* If the geometry looks ok, we're done. */
> > +	if (sbp->sb_blocklog >= XFS_MIN_BLOCKSIZE_LOG &&
> > +	    sbp->sb_blocklog <= XFS_MAX_BLOCKSIZE_LOG &&
> > +	    sbp->sb_blocksize == (1 << sbp->sb_blocklog) &&
> > +	    sbp->sb_dblocks * sbp->sb_blocksize <= x.dsize * x.dbsize &&
> > +	    sbp->sb_dblocks <= XFS_MAX_DBLOCKS(sbp) &&
> > +	    sbp->sb_dblocks >= XFS_MIN_DBLOCKS(sbp))
> > +		return;
> > +
> > +	/* Check blocklog and blocksize */
> > +	blocklog = sbp->sb_blocklog;
> > +	blocksize = sbp->sb_blocksize;
> > +	if (blocklog < XFS_MIN_BLOCKSIZE_LOG ||
> > +	    blocklog > XFS_MAX_BLOCKSIZE_LOG)
> > +		blocklog = libxfs_log2_roundup(blocksize);
> > +	if (blocksize != (1 << blocklog))
> > +		blocksize = (1 << blocksize);
> > +
> > +	/* Clamp dblocks to the size of the device. */
> > +	dblocks = sbp->sb_dblocks;
> > +	if (dblocks > x.dsize * x.dbsize / blocksize)
> > +		dblocks = x.dsize * x.dbsize / blocksize;
> 
> ok now in theory blocksize & dblocks are as good a guess as we can
> get...
> 
> > +
> > +	/* See if agblocks helps us find a superblock. */
> > +	mp->m_blkbb_log = blocklog - BBSHIFT;
> > +	if (sbp->sb_agblocks > 0 && sbp->sb_agblocks <= MAXEXTNUM &&
> > +	    load_sb(mp, 1, &sb) && sb.sb_magicnum == XFS_SB_MAGIC) {
> 
> load_sb translates the one we found into &sb....
> 
> > +		sbp->sb_agcount = dblocks / sbp->sb_agblocks;
> 
> wouldn't it make more sense to just assign from sb->sb_agcount?
> But who's to say the 2nd one isn't corrupt in the same way?
> Grump.

Eh.  Let's instead do the following: If agblocks helps us to find
something with the sb magic we'll suggest that agcount to the user.
In any case we'll set agcount = 1 and let the user sort it out.

> > +		goto out;
> > +	}
> > +
> > +	/* See if agcount helps us find a superblock. */
> 
> Wait I thought agcount problems is why we're here in
> the first place.  What's this for?

Leftover from when I was trying to fix all the geometry parameters.

> > +	agblocks = sbp->sb_agblocks;
> > +	sbp->sb_agblocks = dblocks / sbp->sb_agcount;
> > +	if (sbp->sb_agblocks > 0 && sbp->sb_agblocks <= MAXEXTNUM &&
> > +	    load_sb(mp, 1, &sb) && sb.sb_magicnum == XFS_SB_MAGIC) {
> > +		goto out;
> > +	}
> > +
> > +	/* Both are nuts, assume 1 AG. */
> > +	sbp->sb_agblocks = agblocks;
> > +	sbp->sb_agcount = 1;
> 
> I'd almost rather just jump here and let the admin sort it out...
> 
> But let me play with this a little mmkay?

<shrug> At this point I have a v3 ready so we might as well jump to that.

--D

> 
> -Eric
> 
> > +out:
> > +	fprintf(stderr,
> > +		_("%s: device %s AG count is insane.  Limiting reads to the first %u AGs.\n"),
> > +		progname, fsdevice, sbp->sb_agcount);
> > +}
> > +
> >  void
> >  init(
> >  	int		argc,
> >  	char		**argv)
> >  {
> >  	struct xfs_sb	*sbp;
> > -	struct xfs_buf	*bp;
> >  	int		c;
> >  
> >  	setlocale(LC_ALL, "");
> > @@ -124,20 +207,12 @@ init(
> >  	 */
> >  	memset(&xmount, 0, sizeof(struct xfs_mount));
> >  	libxfs_buftarg_init(&xmount, x.ddev, x.logdev, x.rtdev);
> > -	bp = libxfs_readbuf(xmount.m_ddev_targp, XFS_SB_DADDR,
> > -			    1 << (XFS_MAX_SECTORSIZE_LOG - BBSHIFT), 0, NULL);
> > -
> > -	if (!bp || bp->b_error) {
> > +	if (!load_sb(&xmount, 0, &xmount.m_sb)) {
> >  		fprintf(stderr, _("%s: %s is invalid (cannot read first 512 "
> >  			"bytes)\n"), progname, fsdevice);
> >  		exit(1);
> >  	}
> >  
> > -	/* copy SB from buffer to in-core, converting architecture as we go */
> > -	libxfs_sb_from_disk(&xmount.m_sb, XFS_BUF_TO_SBP(bp));
> > -	libxfs_putbuf(bp);
> > -	libxfs_purgebuf(bp);
> > -
> >  	sbp = &xmount.m_sb;
> >  	if (sbp->sb_magicnum != XFS_SB_MAGIC) {
> >  		fprintf(stderr, _("%s: %s is not a valid XFS filesystem (unexpected SB magic number 0x%08x)\n"),
> > @@ -148,6 +223,8 @@ init(
> >  		}
> >  	}
> >  
> > +	sanitize_geometry(&xmount, sbp);
> > +
> >  	mp = libxfs_mount(&xmount, sbp, x.ddev, x.logdev, x.rtdev,
> >  			  LIBXFS_MOUNT_DEBUGGER);
> >  	if (!mp) {
> > --
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