UBUNTU: SAUCE: LSM stacking: fixup procsfs: add smack subdir to attrs

UBUNTU: SAUCE: LSM stacking: fixup procsfs: add smack subdir to attrs

The patch that adds the smack subdirs also changes how set_procattr
is handled. It makes the assumption that each LSM will attempt
to handle the context written in turn and return ENOENT, if
the LSM doesn't handle the context and another should try.

This is wrong in two ways, LSMs may return ENOENT as an error for
a context that is valid but is not present in currently loaded
policy, and the code is based on earlier versions where each
LSM is tried in turn.

Under the current patchset there is the concept of the current LSM
which will be used by applications using the old interfaces, to
ensure those interfaces which were not designed for multiple LSM
input/out only ever have to deal with a single LSM.

Fixes: 86400b03f812 ("procfs: add smack subdir to attrs")
Signed-off-by: John Johansen <john.johansen@canonical.com>
Signed-off-by: Seth Forshee <seth.forshee@canonical.com>