[PATCH v8 4/4] Landlock: Document LANDLOCK_SCOPED_ABSTRACT_UNIX_SOCKET and ABI versioning

[Tahera Fahimi]

Introducing LANDLOCK_SCOPED_ABSTRACT_UNIX_SOCKET as an IPC scoping
mechanism in Landlock ABI version 6, and updating ruleset_attr,
Landlock ABI version, and access rights code blocks based on that.

Signed-off-by: Tahera Fahimi <fahimitahera at gmail.com>
---
v8:
- Improving documentation by specifying differences between scoped and
  non-scoped domains.
- Adding review notes of version 7.
- Update date
v7:
- Add "LANDLOCK_SCOPED_ABSTRACT_UNIX_SOCKET" explanation to IPC scoping
  section and updating ABI to version 6.
- Adding "scoped" attribute to the Access rights section.
- In current limitation, unnamed sockets are specified as sockets that
  are not restricted.
- Update date
---
 Documentation/userspace-api/landlock.rst | 33 ++++++++++++++++++++++--
 1 file changed, 31 insertions(+), 2 deletions(-)

diff --git a/Documentation/userspace-api/landlock.rst b/Documentation/userspace-api/landlock.rst
index 07b63aec56fa..d602567b5139 100644
--- a/Documentation/userspace-api/landlock.rst
+++ b/Documentation/userspace-api/landlock.rst
@@ -8,7 +8,7 @@ Landlock: unprivileged access control
 =====================================
 
 :Author: Mickaël Salaün
-:Date: April 2024
+:Date: August 2024
 
 The goal of Landlock is to enable to restrict ambient rights (e.g. global
 filesystem or network access) for a set of processes.  Because Landlock
@@ -81,6 +81,8 @@ to be explicit about the denied-by-default access rights.
         .handled_access_net =
             LANDLOCK_ACCESS_NET_BIND_TCP |
             LANDLOCK_ACCESS_NET_CONNECT_TCP,
+        .scoped =
+            LANDLOCK_SCOPED_ABSTRACT_UNIX_SOCKET,
     };
 
 Because we may not know on which kernel version an application will be
@@ -119,6 +121,9 @@ version, and only use the available subset of access rights:
     case 4:
         /* Removes LANDLOCK_ACCESS_FS_IOCTL_DEV for ABI < 5 */
         ruleset_attr.handled_access_fs &= ~LANDLOCK_ACCESS_FS_IOCTL_DEV;
+    case 5:
+        /* Removes LANDLOCK_SCOPED_ABSTRACT_UNIX_SOCKET for ABI < 6 */
+        ruleset_attr.scoped &= ~LANDLOCK_SCOPED_ABSTRACT_UNIX_SOCKET;
     }
 
 This enables to create an inclusive ruleset that will contain our rules.
@@ -306,6 +311,23 @@ To be allowed to use :manpage:`ptrace(2)` and related syscalls on a target
 process, a sandboxed process should have a subset of the target process rules,
 which means the tracee must be in a sub-domain of the tracer.
 
+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 restriction
+with ``LANDLOCK_SCOPED_ABSTRACT_UNIX_SOCKET``.
+
+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 processes in
+the same scoped domain.
+
+IPC scoping does not support Landlock rules, so if a domain is scoped, no rules
+can be added to allow accessing to a resource outside of the scoped domain.
+
 Truncating files
 ----------------
 
@@ -404,7 +426,7 @@ Access rights
 -------------
 
 .. kernel-doc:: include/uapi/linux/landlock.h
-    :identifiers: fs_access net_access
+    :identifiers: fs_access net_access scope
 
 Creating a new ruleset
 ----------------------
@@ -541,6 +563,13 @@ earlier ABI.
 Starting with the Landlock ABI version 5, it is possible to restrict the use of
 :manpage:`ioctl(2)` using the new ``LANDLOCK_ACCESS_FS_IOCTL_DEV`` right.
 
+Abstract Unix sockets Restriction  (ABI < 6)
+--------------------------------------------
+
+With ABI version 6, it is possible to restrict connection to an abstract Unix socket
+through ``LANDLOCK_SCOPED_ABSTRACT_UNIX_SOCKET``, thanks to the ``scoped`` ruleset
+attribute.
+
 .. _kernel_support:
 
 Kernel support
-- 
2.34.1