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

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Message-ID: <20251216210248.4150777-1-samasth.norway.ananda@oracle.com>
Date: Tue, 16 Dec 2025 13:02:42 -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 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 LANDLOCK_RESTRICT_SELF_LOG_*
flags for kernels with ABI < 7.

This introduces the supported_restrict_flags variable which is
initialized with LANDLOCK_RESTRICT_SELF_LOG_NEW_EXEC_ON, removed
in case 6 for ABI < 7, and passed to landlock_restrict_self() to
enable logging on supported kernels.

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 | 22 ++++++++++++++++++----
 1 file changed, 18 insertions(+), 4 deletions(-)

diff --git a/Documentation/userspace-api/landlock.rst b/Documentation/userspace-api/landlock.rst
index 1d0c2c15c22e..b8caac299056 100644
--- a/Documentation/userspace-api/landlock.rst
+++ b/Documentation/userspace-api/landlock.rst
@@ -97,6 +97,8 @@ version, and only use the available subset of access rights:
 .. code-block:: c
 
     int abi;
+    /* Tracks which landlock_restrict_self() flags are supported */
+    int supported_restrict_flags = LANDLOCK_RESTRICT_SELF_LOG_NEW_EXEC_ON;
 
     abi = landlock_create_ruleset(NULL, 0, LANDLOCK_CREATE_RULESET_VERSION);
     if (abi < 0) {
@@ -127,6 +129,17 @@ 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 LANDLOCK_RESTRICT_SELF_LOG_NEW_EXEC_ON for ABI < 7.
+         * Note: This modifies supported_restrict_flags, not ruleset_attr,
+         * because logging flags are passed to landlock_restrict_self().
+         */
+        supported_restrict_flags &= ~LANDLOCK_RESTRICT_SELF_LOG_NEW_EXEC_ON;
+        __attribute__((fallthrough));
+    case 7:
+        break;
     }
 
 This enables the creation of an inclusive ruleset that will contain our rules.
@@ -142,8 +155,9 @@ 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.
@@ -193,7 +207,7 @@ number for a specific action: HTTPS connections.
 
 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
+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
@@ -208,7 +222,7 @@ The current thread is now ready to sandbox itself with the ruleset.
 
 .. code-block:: c
 
-    if (landlock_restrict_self(ruleset_fd, 0)) {
+    if (landlock_restrict_self(ruleset_fd, supported_restrict_flags)) {
         perror("Failed to enforce ruleset");
         close(ruleset_fd);
         return 1;
-- 
2.50.1