landlock: Add API support and docs for the quiet flags

Adds the UAPI for the quiet flags feature (but not the implementation
yet).

Even though currently LANDLOCK_ADD_RULE_QUIET only affects audit
logging, in the future this can also be used as part of a supervisor
mechanism, where it will also suppress denial notifications on a
per-object basis.  Thus the name is deliberately generic, as opposed to
e.g. LANDLOCK_ADD_RULE_LOG_QUIET.

According to pahole, even after adding the struct access_masks
quiet_masks in struct landlock_hierarchy, the u32 log_* bitfield still
only has a size of 2 bytes, so there's minimal wasted space.

Assisted-by: GitHub-Copilot:claude-opus-4.8
Signed-off-by: Tingmao Wang <m@maowtm.org>
[mic: Update date, fix comment formatting]
Link: https://patch.msgid.link/031184748a8e74c0bb02f1fa13d7a3f10918c627.1781228815.git.m@maowtm.org
Signed-off-by: Mickaël Salaün <mic@digikod.net>

1 files changed, 60 insertions, 0 deletions

diff --git a/include/uapi/linux/landlock.h b/include/uapi/linux/landlock.h
index 811ec77f9105..7ffe2ef127ee 100644
--- a/include/uapi/linux/landlock.h
+++ b/include/uapi/linux/landlock.h
@@ -32,6 +32,19 @@
  * *handle* a wide range or all access rights that they know about at build time
  * (and that they have tested with a kernel that supported them all).
  *
+ * @quiet_access_fs and @quiet_access_net are bitmasks of actions for which a
+ * denial by this layer will not trigger a log if the corresponding object (or
+ * its children, for filesystem rules) is marked with the "quiet" bit via
+ * %LANDLOCK_ADD_RULE_QUIET, even if logging would normally take place per
+ * landlock_restrict_self() flags.  @quiet_scoped is similar, except that it
+ * does not require marking any objects as quiet - if the ruleset is created
+ * with any bits set in @quiet_scoped, then denial of such scoped resources will
+ * not trigger any log.  These 3 fields are available since Landlock ABI version
+ * 10.
+ *
+ * @quiet_access_fs, @quiet_access_net and @quiet_scoped must be a subset of
+ * @handled_access_fs, @handled_access_net and @scoped respectively.
+ *
  * This structure can grow in future Landlock versions.
  */
 struct landlock_ruleset_attr {
@@ -51,6 +64,20 @@ struct landlock_ruleset_attr {
 	 * resources (e.g. IPCs).
 	 */
 	__u64 scoped;
+	/**
+	 * @quiet_access_fs: Bitmask of filesystem actions which should not be
+	 * logged if per-object quiet flag is set.
+	 */
+	__u64 quiet_access_fs;
+	/**
+	 * @quiet_access_net: Bitmask of network actions which should not be
+	 * logged if per-object quiet flag is set.
+	 */
+	__u64 quiet_access_net;
+	/**
+	 * @quiet_scoped: Bitmask of scoped actions which should not be logged.
+	 */
+	__u64 quiet_scoped;
 };
 
 /**
@@ -70,6 +97,39 @@ struct landlock_ruleset_attr {
 /* clang-format on */
 
 /**
+ * DOC: landlock_add_rule_flags
+ *
+ * **Flags**
+ *
+ * %LANDLOCK_ADD_RULE_QUIET
+ *     Together with the quiet_* fields in struct landlock_ruleset_attr,
+ *     this flag controls whether Landlock will log audit messages when
+ *     access to the objects covered by this rule is denied by this layer.
+ *
+ *     If logging is enabled, when Landlock denies an access, it will
+ *     suppress the log if all of the following are true:
+ *
+ *     - this layer is the innermost layer that denied the access;
+ *     - all accesses denied by this layer are part of the quiet_* fields
+ *       in the related struct landlock_ruleset_attr;
+ *     - the object (or one of its parents, for filesystem rules) is
+ *       marked as "quiet" via %LANDLOCK_ADD_RULE_QUIET.
+ *
+ *     Because logging is only suppressed by a layer if the layer denies
+ *     access, a sandboxed program cannot use this flag to "hide" access
+ *     denials, without denying itself the access in the first place.
+ *
+ *     The effect of this flag does not depend on the value of
+ *     allowed_access in the passed in rule_attr.  When this flag is
+ *     present, the caller is also allowed to pass in an empty
+ *     allowed_access.
+ */
+
+/* clang-format off */
+#define LANDLOCK_ADD_RULE_QUIET			(1U << 0)
+/* clang-format on */
+
+/**
  * DOC: landlock_restrict_self_flags
  *
  * **Flags**