[PATCH 2/9] metadump: bounds check btree block regions being zeroed

[Brian Foster]

On Tue, Dec 22, 2015 at 08:37:02AM +1100, Dave Chinner wrote:
> From: Dave Chinner <dchinner at redhat.com>
> 
> Arkadiusz Miskiewicz reported that metadump was crashing on one of
> his corrupted filesystems, and the trace indicated that it was
> zeroing unused regions in inode btree blocks when it failed. The
> btree block had a corrupt nrecs field, which was resulting in an out
> of bounds memset() occurring.  Ensure that the region being
> generated for zeroing is within bounds before executing the zeroing.
> 
> Reported-by: Arkadiusz Miskiewicz <arekm at maven.pl>
> Signed-off-by: Dave Chinner <dchinner at redhat.com>
> ---
>  db/metadump.c | 32 ++++++++++++++++++++++++++++++++
>  1 file changed, 32 insertions(+)
> 
> diff --git a/db/metadump.c b/db/metadump.c
> index a185da5..1769fdf 100644
> --- a/db/metadump.c
> +++ b/db/metadump.c
...
> @@ -300,6 +316,11 @@ zero_btree_node(
>  	memset(zp2, 0, (char *)block + mp->m_sb.sb_blocksize - zp2);
>  }
>  
> +/*
> + * We could be processing a corrupt block, so we can't trust any of
> + * the offsets or lengths to be within the buffer range. Hence check
> + * carefully!
> + */
>  static void
>  zero_btree_leaf(
>  	struct xfs_btree_block	*block,
> @@ -312,20 +333,31 @@ zero_btree_leaf(
>  	char			*zp;
>  
>  	nrecs = be16_to_cpu(block->bb_numrecs);
> +	if (nrecs < 0)
> +		return;
>  
>  	switch (btype) {
>  	case TYP_BMAPBTA:
>  	case TYP_BMAPBTD:
> +		if (nrecs > mp->m_bmap_dmxr[1])
> +			return;
> +

Shouldn't we use the 0 index max recs value (for leaf blocks) throughout
this function? (e.g, mp->m_bmap_dmxr[0])

Brian

>  		brp = XFS_BMBT_REC_ADDR(mp, block, 1);
>  		zp = (char *)&brp[nrecs];
>  		break;
>  	case TYP_INOBT:
>  	case TYP_FINOBT:
> +		if (nrecs > mp->m_inobt_mxr[1])
> +			return;
> +
>  		irp = XFS_INOBT_REC_ADDR(mp, block, 1);
>  		zp = (char *)&irp[nrecs];
>  		break;
>  	case TYP_BNOBT:
>  	case TYP_CNTBT:
> +		if (nrecs > mp->m_alloc_mxr[1])
> +			return;
> +
>  		arp = XFS_ALLOC_REC_ADDR(mp, block, 1);
>  		zp = (char *)&arp[nrecs];
>  		break;
> -- 
> 2.5.0
> 
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