/usr/lib/x86_64-linux-gnu/libSM.so.6 is in libsm6 2:1.2.2-1+b1.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/lib/x86_64-linux-gnu/libSM.so.6.0.1
/usr/lib/x86_64-linux-gnu/libSM.so.6.0.1