xfs: assert a valid limit in xfs_rtfind_forw

commit 6d2db12d56 upstream.

Protect against developers passing stupid limits when refactoring the
RT code once again.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Darrick J. Wong <djwong@kernel.org>
Signed-off-by: Darrick J. Wong <djwong@kernel.org>
Signed-off-by: Catherine Hoang <catherine.hoang@oracle.com>
Acked-by: Darrick J. Wong <djwong@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

fs/xfs/libxfs/xfs_rtbitmap.c

@@ -288,6 +288,8 @@ xfs_rtfind_forw(
 	xfs_rtword_t	wdiff;		/* difference from wanted value */
 	int		word;		/* word number in the buffer */
 
+	ASSERT(start <= limit);
+
 	/*
 	 * Compute and read in starting bitmap block for starting block.
 	 */