linux-kernel - [PATCH v2 1/3] landlock: Add missing ABI 7 case in documentation example

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Message-ID: <20260103002722.1465371-2-samasth.norway.ananda@oracle.com>
Date: Fri,  2 Jan 2026 16:27:13 -0800
From: Samasth Norway Ananda <samasth.norway.ananda@...cle.com>
To: mic@...ikod.net, gnoack@...gle.com
Cc: linux-security-module@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: [PATCH v2 1/3] landlock: Add missing ABI 7 case in documentation example

Add the missing case 6 and case 7 handling in the ABI version
compatibility example to properly handle ABI < 7 kernels.

Add an optional backwards compatibility section for restrict flags
between the case analysis and landlock_restrict_self() call. The main
tutorial example remains unchanged with
landlock_restrict_self(ruleset_fd, 0) to keep it simple for users who
don't need logging flags.

Also fix misleading description of the /usr rule which incorrectly
stated it "only allow[s] reading" when the code actually allows both
reading and executing (LANDLOCK_ACCESS_FS_EXECUTE is included in
allowed_access).

Signed-off-by: Samasth Norway Ananda <samasth.norway.ananda@...cle.com>
---
 Documentation/userspace-api/landlock.rst | 35 +++++++++++++++++++++---
 1 file changed, 31 insertions(+), 4 deletions(-)

diff --git a/Documentation/userspace-api/landlock.rst b/Documentation/userspace-api/landlock.rst
index 1d0c2c15c22e..650c7b368561 100644
--- a/Documentation/userspace-api/landlock.rst
+++ b/Documentation/userspace-api/landlock.rst
@@ -127,6 +127,12 @@ 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:
+        /* Removes logging flags for ABI < 7 */
+        __attribute__((fallthrough));
+    case 7:
+        break;
     }
 
 This enables the creation of an inclusive ruleset that will contain our rules.
@@ -142,8 +148,9 @@ This enables the creation of an inclusive ruleset that will contain our rules.
     }
 
 We can now add a new rule to this ruleset thanks to the returned file
-descriptor referring to this ruleset.  The rule will only allow reading the
-file hierarchy ``/usr``.  Without another rule, write actions would then be
+descriptor referring to this ruleset.  The rule will allow reading and
+executing files in the ``/usr`` hierarchy.  Without another rule, write actions
+and other operations (make_dir, remove_file, etc.) would then be
 denied by the ruleset.  To add ``/usr`` to the ruleset, we open it with the
 ``O_PATH`` flag and fill the &struct landlock_path_beneath_attr with this file
 descriptor.
@@ -191,10 +198,30 @@ number for a specific action: HTTPS connections.
     err = landlock_add_rule(ruleset_fd, LANDLOCK_RULE_NET_PORT,
                             &net_port, 0);
 
+Backwards compatibility for restrict flags
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+When passing a non-zero ``flags`` argument to ``landlock_restrict_self()``, the
+following backwards compatibility check needs to be taken into account:
+
+.. code-block:: c
+
+    /*
+     * Desired restriction flags, see ABI version section above.
+     * This value is only an example and differs by use case.
+     */
+    int restrict_flags = LANDLOCK_RESTRICT_SELF_LOG_NEW_EXEC_ON;
+    if (abi < 7) {
+        /* Clear logging flags unsupported in ABI < 7 */
+        restrict_flags &= ~(LANDLOCK_RESTRICT_SELF_LOG_SAME_EXEC_OFF |
+                           LANDLOCK_RESTRICT_SELF_LOG_NEW_EXEC_ON |
+                           LANDLOCK_RESTRICT_SELF_LOG_SUBDOMAINS_OFF);
+    }
+
 The next step is to restrict the current thread from gaining more privileges
 (e.g. through a SUID binary).  We now have a ruleset with the first rule
-allowing read access to ``/usr`` while denying all other handled accesses for
-the filesystem, and a second rule allowing HTTPS connections.
+allowing read and execute access to ``/usr`` while denying all other handled
+accesses for the filesystem, and a second rule allowing HTTPS connections.
 
 .. code-block:: c
 
-- 
2.50.1