Re: [PATCH v4] libxfs: add more bounds checking to sb sanity checks

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

On Thu, Jul 26, 2018 at 11:40:46AM -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>
> ---
> 
> v4: adjust control flow to standard error checking. Add
>     more descriptive comment. Add validation for sb_icount.
> v3: eliminate need for additional write_flag, doing those
>     unique checks in xfs_sb_write_verify()
> v2: make extra sanity checks exclusive to writes
> 
>  fs/xfs/libxfs/xfs_sb.c | 46 +++++++++++++++++++++++++++++++++---------
>  1 file changed, 36 insertions(+), 10 deletions(-)
> 
> diff --git a/fs/xfs/libxfs/xfs_sb.c b/fs/xfs/libxfs/xfs_sb.c
> index b3ad15956366..8d8e579ca426 100644
> --- a/fs/xfs/libxfs/xfs_sb.c
> +++ b/fs/xfs/libxfs/xfs_sb.c
> @@ -599,22 +599,16 @@ xfs_sb_to_disk(
>  static int
>  xfs_sb_verify(
>  	struct xfs_buf	*bp,
> +	struct xfs_sb	*sb,
>  	bool		check_version)
>  {
>  	struct xfs_mount *mp = bp->b_target->bt_mount;
> -	struct xfs_sb	sb;
> -
> -	/*
> -	 * Use call variant which doesn't convert quota flags from disk 
> -	 * format, because xfs_mount_validate_sb checks the on-disk flags.
> -	 */
> -	__xfs_sb_from_disk(&sb, XFS_BUF_TO_SBP(bp), false);
>  
>  	/*
>  	 * Only check the in progress field for the primary superblock as
>  	 * mkfs.xfs doesn't clear it from secondary superblocks.
>  	 */
> -	return xfs_mount_validate_sb(mp, &sb,
> +	return xfs_mount_validate_sb(mp, sb,
>  				     bp->b_maps[0].bm_bn == XFS_SB_DADDR,
>  				     check_version);
>  }
> @@ -637,6 +631,7 @@ xfs_sb_read_verify(
>  {
>  	struct xfs_mount *mp = bp->b_target->bt_mount;
>  	struct xfs_dsb	*dsb = XFS_BUF_TO_SBP(bp);
> +	struct xfs_sb	sb;
>  	int		error;
>  
>  	/*
> @@ -657,7 +652,13 @@ xfs_sb_read_verify(
>  			}
>  		}
>  	}
> -	error = xfs_sb_verify(bp, true);
> +
> +	/*
> +	 * Use call variant which doesn't convert quota flags from disk
> +	 * format, because xfs_mount_validate_sb checks the on-disk flags.
> +	 */
> +	__xfs_sb_from_disk(&sb, XFS_BUF_TO_SBP(bp), false);
> +	error = xfs_sb_verify(bp, &sb, true);
>  
>  out_error:
>  	if (error == -EFSCORRUPTED || error == -EFSBADCRC)
> @@ -693,9 +694,34 @@ xfs_sb_write_verify(
>  {
>  	struct xfs_mount	*mp = bp->b_target->bt_mount;
>  	struct xfs_buf_log_item	*bip = bp->b_log_item;
> +	struct xfs_sb		sb;
>  	int			error;
>  
> -	error = xfs_sb_verify(bp, false);
> +	/*
> +	 * Use call variant which doesn't convert quota flags from disk
> +	 * format, because xfs_mount_validate_sb checks the on-disk flags.
> +	 */
> +	__xfs_sb_from_disk(&sb, XFS_BUF_TO_SBP(bp), false);
> +
> +	error = xfs_sb_verify(bp, &sb, false);
> +	if (error)
> +		goto err;
> +
> +	/*
> +	 * Carry out additional sb sanity checks exclusively for writes.
> +	 * We don't do these checks for reads, since faulty parameters could
> +	 * already be on disk, and we shouldn't preclude reads for those
> +	 * cases.
> +	 */
> +	if (sb.sb_fdblocks > sb.sb_dblocks ||
> +	    sb.sb_icount / sb.sb_inopblock > sb.sb_dblocks ||

This is a 64-bit division, which won't work on 32-bit builds.

That said, I also wrote a xfs_verify_icount function for the fs summary
scrub patch, so perhaps we should collaborate to land both of these?
Send a v5 without this test and I'll immediately send a patch adding
both the _verify_icount and putting it to use here.

Actually, I could just modify your patch, add mine, and send both of
them.  That'd be easier...

--D

> +	    sb.sb_ifree > sb.sb_icount) {
> +		xfs_notice(mp, "SB sanity check failed");
> +		error = -EFSCORRUPTED;
> +		goto err;
> +	}
> +
> +err:
>  	if (error) {
>  		xfs_verifier_error(bp, error, __this_address);
>  		return;
> -- 
> 2.17.1
> 
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