Fix for buffer overflow in ldm_frag_add not sufficient

As Ben Hutchings discovered [1], the patch for CVE-2011-1017 (buffer
overflow in ldm_frag_add) is not sufficient.  The original patch in
commit c340b1d64000 ("fs/partitions/ldm.c: fix oops caused by corrupted
partition table") does not consider that, for subsequent fragments,
previously allocated memory is used.

[1] http://lkml.org/lkml/2011/5/6/407

Reported-by: Ben Hutchings <ben@decadent.org.uk>
Signed-off-by: Timo Warns <warns@pre-sense.de>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
static u64 ldm_get_vnum (const u8 *block)
{
	u64 tmp = 0;
	u8 length;

	BUG_ON (!block);

	length = *block++;

	if (length && length <= 8)
		while (length--)
			tmp = (tmp << 8) | *block++;
	else
		ldm_error ("Illegal length %d.", length);

	return tmp;
}

static u64 ldm_get_vnum (const u8 *block)
{
	u64 tmp = 0;
	u8 length;

	BUG_ON (!block);

	length = *block++;

	if (length && length <= 8)
		while (length--)
			tmp = (tmp << 8) | *block++;
	else
		ldm_error ("Illegal length %d.", length);

	return tmp;
}
