Re: [PATCH] xfs: check da node magic in _node_lookup_int

[Dave Chinner <david@fromorbit.com>]

On Tue, Jul 31, 2018 at 01:03:56PM -0700, Darrick J. Wong wrote:
> From: Darrick J. Wong <darrick.wong@oracle.com>
> 
> Before we start processing what we /think/ is a da3 node block, actually
> check the magic to make sure that we're looking at a node block.  This
> way we won't blow the asserts in _node_hdr_from_disk on corrupted
> metadata.
> 
> Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
> ---
>  fs/xfs/libxfs/xfs_da_btree.c |    5 ++++-
>  1 file changed, 4 insertions(+), 1 deletion(-)
> 
> diff --git a/fs/xfs/libxfs/xfs_da_btree.c b/fs/xfs/libxfs/xfs_da_btree.c
> index 9efbd2038ffb..70e7da634f3e 100644
> --- a/fs/xfs/libxfs/xfs_da_btree.c
> +++ b/fs/xfs/libxfs/xfs_da_btree.c
> @@ -1522,8 +1522,11 @@ xfs_da3_node_lookup_int(
>  			break;
>  		}
>  
> -		blk->magic = XFS_DA_NODE_MAGIC;
> +		if (blk->magic != XFS_DA_NODE_MAGIC &&
> +		    blk->magic != XFS_DA3_NODE_MAGIC)
> +			return -EFSCORRUPTED;
>  
> +		blk->magic = XFS_DA_NODE_MAGIC;

Can we please use a temporary variable for the on-disk magic number
checks, then? blk->magic isn't supposed to hold the on disk format
magic number - it's just an indication of the format the current
state block points at - so using it to temporarily store the on disk
magic number for checks like this is just wrong....

Cheers,

Dave.
-- 
Dave Chinner
david@fromorbit.com