I found the answer. makejail program preserve permissions so there is no problem with jail directory created by makejail.
But deb helper scripts disturb every thing. on a default debian/rules file dh_fixperms run and change permissions so /bin/bash is not executable any more! to fix this problem we should overwrite dh_perms with this rule:
override_dh_perms:
every this get sweeter with this line!