  Protection of confidential data is an important security consideration of
today's applications. Of particular concern is to guard against unintentional
leakage to a (malicious) observer, who may interact with the program and draw
inference from made observations. Information flow control (IFC) type systems
address this concern by statically ruling out such leakage. This paper
contributes an IFC type system for message-passing concurrent programs, the
computational model of choice for many of today's applications such as cloud
computing and IoT applications. Such applications typically either implicitly
or explicitly codify protocols according to which message exchange must happen,
and to statically ensure protocol safety, behavioral type systems such as
session types can be used. This paper marries IFC with session typing and
contributes over prior work in the following regards: (1) support of realistic
cyclic process networks as opposed to the restriction to tree-shaped networks,
(2) more permissive, yet entirely secure, IFC control, exploiting cyclic
process networks, and (3) considering deadlocks as another form of side
channel, and asserting deadlock-sensitive noninterference (DSNI) for well-typed
programs. To prove DSNI, the paper develops a novel logical relation that
accounts for cyclic process networks. The logical relation is rooted in linear
logic, but drops the tree-topology restriction imposed by prior work.
