[PATCH 2/2] landlock: Clarify IPC scoping documentation

[Günther Noack]

* Clarify terminology
* Stop mixing the unix(7) and signal(7) aspects in the explanation.

Terminology:

* The *IPC Scope* of a Landlock domain is that Landlock domain and its
  nested domains.
* An *operation* (e.g., signaling, connecting to abstract UDS) is said
  *to be scoped within a domain* when the flag for that operation was
  *set at ruleset creation time.  This means that for the purpose of
  *this operation, only processes within the domain's IPC scope are
  *reachable.

Cc: Mickaël Salaün <mic at digikod.net>
Cc: Tahera Fahimi <fahimitahera at gmail.com>
Cc: Tanya Agarwal <tanyaagarwal25699 at gmail.com>
Signed-off-by: Günther Noack <gnoack at google.com>
---
 Documentation/userspace-api/landlock.rst | 53 ++++++++++++------------
 1 file changed, 26 insertions(+), 27 deletions(-)

diff --git a/Documentation/userspace-api/landlock.rst b/Documentation/userspace-api/landlock.rst
index ca8b325d53e5..6b80106d33de 100644
--- a/Documentation/userspace-api/landlock.rst
+++ b/Documentation/userspace-api/landlock.rst
@@ -317,33 +317,32 @@ IPC scoping
 -----------
 
 Similar to the implicit `Ptrace restrictions`_, we may want to further restrict
-interactions between sandboxes. Each Landlock domain can be explicitly scoped
-for a set of actions by specifying it on a ruleset.  For example, if a
-sandboxed process should not be able to :manpage:`connect(2)` to a
-non-sandboxed process through abstract :manpage:`unix(7)` sockets, we can
-specify such a restriction with ``LANDLOCK_SCOPE_ABSTRACT_UNIX_SOCKET``.
-Moreover, if a sandboxed process should not be able to send a signal to a
-non-sandboxed process, we can specify this restriction with
-``LANDLOCK_SCOPE_SIGNAL``.
-
-A sandboxed process can connect to a non-sandboxed process when its domain is
-not scoped. If a process's domain is scoped, it can only connect to sockets
-created by processes in the same scope.
-Moreover, if a process is scoped to send signal to a non-scoped process, it can
-only send signals to processes in the same scope.
-
-A connected datagram socket behaves like a stream socket when its domain is
-scoped, meaning if the domain is scoped after the socket is connected, it can
-still :manpage:`send(2)` data just like a stream socket.  However, in the same
-scenario, a non-connected datagram socket cannot send data (with
-:manpage:`sendto(2)`) outside its scope.
-
-A process with a scoped domain can inherit a socket created by a non-scoped
-process. The process cannot connect to this socket since it has a scoped
-domain.
-
-IPC scoping does not support exceptions, so if a domain is scoped, no rules can
-be added to allow access to resources or processes outside of the scope.
+interactions between sandboxes.  Therefore, at ruleset creation time, each
+Landlock domain can restrict the scope for certain operations, so that these
+operations can only reach out to processes within the same Landlock domain or in
+a nested Landlock domain (the "scope").
+
+The operations which can be scoped are:
+
+``LANDLOCK_SCOPE_SIGNAL``
+    When set, this limits the sending of signals to target processes which run
+    within the same or a nested Landlock domain.
+
+``LANDLOCK_SCOPE_ABSTRACT_UNIX_SOCKET``
+    When set, this limits the set of abstract :manpage:`unix(7)` sockets we can
+    :manpage:`connect(2)` to to socket addresses which were created by a process
+    in the same or a nested Landlock domain.
+
+    A :manpage:`send(2)` on a non-connected datagram socket is treated like an
+    implicit :manpage:`connect(2)` and will be blocked when the remote end does
+    not stem from the same or a nested Landlock domain.
+
+    A :manpage:`send(2)` on a socket which was previously connected will work.
+    This works for both datagram and stream sockets.
+
+IPC scoping does not support exceptions via :manpage:`landlock_add_rule(2)`.
+If an operation is scoped within a domain, no rules can be added to allow access
+to resources or processes outside of the scope.
 
 Truncating files
 ----------------
-- 
2.48.1.262.g85cc9f2d1e-goog