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

Brian Foster
2016-01-04T19:12:02Z

On Tue, Dec 22, 2015 at 08:37:02AM +1100, Dave Chinner wrote:
> From: Dave Chinner <dchinner@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@maven.pl>
> Signed-off-by: Dave Chinner <dchinner@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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