[PATCH v7 11/11] landlock: Document FS access right for pathname UNIX sockets

["Günther Noack" <gnoack3000@gmail.com>]

Add LANDLOCK_ACCESS_FS_RESOLVE_UNIX to the example code, and explain
it in the section about previous limitations.  The bulk of the
interesting flag documentation lives in the kernel header and is
included in the Sphinx rendering.

Cc: Justin Suess <utilityemal77@gmail.com>
Cc: Mickaël Salaün <mic@digikod.net>
Signed-off-by: Günther Noack <gnoack3000@gmail.com>
---
 Documentation/userspace-api/landlock.rst | 14 +++++++++++++-
 1 file changed, 13 insertions(+), 1 deletion(-)

diff --git a/Documentation/userspace-api/landlock.rst b/Documentation/userspace-api/landlock.rst
index 13134bccdd39..318d0d8a16da 100644
--- a/Documentation/userspace-api/landlock.rst
+++ b/Documentation/userspace-api/landlock.rst
@@ -77,7 +77,8 @@ to be explicit about the denied-by-default access rights.
             LANDLOCK_ACCESS_FS_MAKE_SYM |
             LANDLOCK_ACCESS_FS_REFER |
             LANDLOCK_ACCESS_FS_TRUNCATE |
-            LANDLOCK_ACCESS_FS_IOCTL_DEV,
+            LANDLOCK_ACCESS_FS_IOCTL_DEV |
+            LANDLOCK_ACCESS_FS_RESOLVE_UNIX,
         .handled_access_net =
             LANDLOCK_ACCESS_NET_BIND_TCP |
             LANDLOCK_ACCESS_NET_CONNECT_TCP,
@@ -127,6 +128,10 @@ version, and only use the available subset of access rights:
         /* Removes LANDLOCK_SCOPE_* for ABI < 6 */
         ruleset_attr.scoped &= ~(LANDLOCK_SCOPE_ABSTRACT_UNIX_SOCKET |
                                  LANDLOCK_SCOPE_SIGNAL);
+        __attribute__((fallthrough));
+    case 6 ... 8:
+        /* Removes LANDLOCK_ACCESS_FS_RESOLVE_UNIX for ABI < 9 */
+        ruleset_attr.handled_access_fs &= ~LANDLOCK_ACCESS_FS_RESOLVE_UNIX;
     }
 
 This enables the creation of an inclusive ruleset that will contain our rules.
@@ -685,6 +690,13 @@ enforce Landlock rulesets across all threads of the calling process
 using the ``LANDLOCK_RESTRICT_SELF_TSYNC`` flag passed to
 sys_landlock_restrict_self().
 
+Pathname UNIX sockets (ABI < 9)
+-------------------------------
+
+Starting with the Landlock ABI version 9, it is possible to restrict
+connections to pathname UNIX domain sockets (:manpage:`unix(7)`) using
+the new ``LANDLOCK_ACCESS_FS_RESOLVE_UNIX`` right.
+
 .. _kernel_support:
 
 Kernel support
-- 
2.53.0