/usr/lib/mono/4.0/System.ServiceModel.dll is in libmono-system-servicemodel4.0-cil 2.10.8.1-8+deb7u1.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/lib/mono/4.0/../gac/System.ServiceModel/4.0.0.0__b77a5c561934e089/System.ServiceModel.dll