Re: [PATCH v5 1/5] xfs_db: sanitize geometry on load

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

On Fri, Jan 20, 2017 at 04:15:05PM -0800, 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.
> v3: Suggest a possible agcount value, but always restrict to 1 AG.
> v4: Remove the suggested agcount value and make sure we can't exit
> the program with an exitcode of zero.
> v5: remove global variables and unnecessary parameters
> ---
>  db/init.c |   89 +++++++++++++++++++++++++++++++++++++++++++++++++++++--------
>  1 file changed, 77 insertions(+), 12 deletions(-)
> 
> diff --git a/db/init.c b/db/init.c
> index ec1e274..0c684a5 100644
> --- a/db/init.c
> +++ b/db/init.c
> @@ -51,13 +51,81 @@ usage(void)
>  	exit(1);
>  }
>  
> +/* Try to load a superblock for the given agno, no verifiers. */
> +static bool
> +load_sb(
> +	struct xfs_mount	*mp,
> +	struct xfs_sb		*sbp)
> +{
> +	struct xfs_buf		*bp;
> +
> +	bp = libxfs_readbuf(mp->m_ddev_targp, 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 agcount doesn't look sane, suggest a real agcount to the user,
> + * and pretend agcount = 1 to avoid OOMing libxfs_initialize_perag.
> + * Returns true if the geometry was sane.
> + */
> +static bool
> +sanitize_geometry(
> +	struct xfs_mount	*mp,
> +	struct xfs_sb		*sbp)
> +{
> +	unsigned int		blocklog;
> +	unsigned int		blocksize;
> +	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 true;
> +
> +	/* 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;

NAK, this is dead code and the comments are wrong.  Sending v6.

--D

> +
> +	/* Assume 1 AG to avoid OOM. */
> +	fprintf(stderr,
> +_("%s: device %s AG count is insane.  Limiting reads to AG 0.\n"),
> +		progname, fsdevice);
> +	sbp->sb_agcount = 1;
> +
> +	return false;
> +}
> +
>  void
>  init(
>  	int		argc,
> -	char		**argv)
> +	char		**argv,
> +	bool		*insane_agcount)
>  {
>  	struct xfs_sb	*sbp;
> -	struct xfs_buf	*bp;
>  	int		c;
>  
>  	setlocale(LC_ALL, "");
> @@ -124,20 +192,12 @@ 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, &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 +208,8 @@ init(
>  		}
>  	}
>  
> +	*insane_agcount = !sanitize_geometry(&xmount, sbp);
> +
>  	mp = libxfs_mount(&xmount, sbp, x.ddev, x.logdev, x.rtdev,
>  			  LIBXFS_MOUNT_DEBUGGER);
>  	if (!mp) {
> @@ -190,10 +252,11 @@ main(
>  	int	c, i, done = 0;
>  	char	*input;
>  	char	**v;
> +	bool	insane_agcount;
>  	int	start_iocur_sp;
>  
>  	pushfile(stdin);
> -	init(argc, argv);
> +	init(argc, argv, &insane_agcount);
>  	start_iocur_sp = iocur_sp;
>  
>  	for (i = 0; !done && i < ncmdline; i++) {
> @@ -230,5 +293,7 @@ main(
>  		libxfs_device_close(x.logdev);
>  	if (x.rtdev)
>  		libxfs_device_close(x.rtdev);
> +	if (insane_agcount && exitcode == 0)
> +		exitcode = 1;
>  	return exitcode;
>  }
> --
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