[Ocfs2-tools-devel] [PATCH] fix wrap assignment for extended slot map in ocfs2_store_slot_map()

[Joel Becker]

On Mon, Jun 15, 2009 at 04:06:00PM +0800, Coly Li wrote:
> in ocfs2_store_slot_map(), no matter extended slot map is used, only wrap.mw_map
> is initialized, which will introduce a wild memory accessing when extended slot
> map is used.

	The slot_map_wrapper structure is a union.  That is, the address
of mw_map and mw_map_extended is the same.  There's no wild memory
access because merely accessing the union's addresses doesn't select
which portion of the union is used later.

> @@ -334,7 +334,12 @@ errcode_t ocfs2_store_slot_map(ocfs2_filesys *fs,
>  	ret = ocfs2_malloc0(bytes, &slot_map_buf);
>  	if (ret)
>  		return ret;
> -	wrap.mw_map = (struct ocfs2_slot_map *)slot_map_buf;
> +
> +	if (extended)
> +		wrap.mw_map_extended =
> +			(struct ocfs2_slot_map_extened *)slot_map_buf;
> +	else
> +		wrap.mw_map = (struct ocfs2_slot_map *)slot_map_buf;

	Your change makes explicit what C considers implicit.  It's a
union of one pointer.  That pointer can be named mw_map_extended or
mw_map, but it's the same pointer.  So the code

	wrap.mw_map = (struct ocfs2_slot_map *)slot_map_buf;

is equivalent to:

	(char *)wrap.mw_map = slot_map_buf;

It is just setting the pointer, with casts making sure that the compiler
does not complain.  Higher up in ocfs2_store_slot_map(), we make sure
the buffer is big enough and we zero it out.
	So, NAK, the code is correct as-is.

Joel

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Joel Becker
Principal Software Developer
Oracle
E-mail: joel.becker at oracle.com
Phone: (650) 506-8127