Cut square tube subdivision mesh

How to cut with a right angle a subdivision mesh.
Want to cut with the knife tool a hollow square tube with a shell and a skew end also used subdivision for more natural look.
But now the knife tool is not a straight line anymore. Follows the subdivision edge loops after enter.

Are you aware of adding sharp edges with subsurf?

Yes I am but I prefer adding edge loops.

Can you share a screenshot for what you want to achieve/ the problem with knife tool?

Solved had to disable subdivision.