[PATCH v2 3/3] landlock.7: Clarify IPC scoping documentation in line with kernel side

Günther Noack
2025-02-26T21:29:32Z

* 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.

Link: https://lore.kernel.org/all/20250226211814.31420-4-gnoack@google.com/
Signed-off-by: Günther Noack <gnoack@google.com>
---
man/man7/landlock.7 | 73 ++++++++++++++++++++++-----------------------
1 file changed, 35 insertions(+), 38 deletions(-)

diff --git a/man/man7/landlock.7 b/man/man7/landlock.7
index 30dbac73d..42cd7286f 100644
--- a/man/man7/landlock.7
+++ b/man/man7/landlock.7
@@ -357,46 +357,43 @@ which means the tracee must be in a sub-domain of the tracer.
Similar to the implicit
.BR "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
-.BR connect (2)
-to a non-sandboxed process through abstract
+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").
+.P
+The operations which can be scoped are:
+.P
+.TP
+.B LANDLOCK_SCOPE_SIGNAL
+This limits the sending of signals to target processes
+which run within the same or a nested Landlock domain.
+.TP
+.B LANDLOCK_SCOPE_ABSTRACT_UNIX_SOCKET
+This limits the set of abstract
.BR unix (7)
-sockets,
-we can specify such a restriction with
-.BR 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
-.BR LANDLOCK_SCOPE_SIGNAL .
+sockets to which we can
+.BR connect (2)
+to socket addresses which were created
+by a process in the same or a nested Landlock domain.
+.IP
+A
+.BR sendto (2)
+on a non-connected datagram socket is treated as if it were doing an implicit
+.BR connect (2)
+and will be blocked if the remote end does not stem
+from the same or a nested Landlock domain.
+.IP
+A
+.BR sendto (2)
+on a socket which was previously connected will not be restricted.
+This works for both datagram and stream sockets.
.P
-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.
-.P
-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
-.BR send (2)
-data just like a stream socket.
-However, in the same scenario,
-a non-connected datagram socket cannot send data (with
-.BR sendto (2))
-outside its scope.
-.P
-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.
-.P
-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.
+IPC scoping does not support exceptions via
+.BR 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.
.\"
.SS Truncating files
The operations covered by
--
2.48.1.711.g2feabab25a-goog