landlock: Optimize scope enforcement

Do not walk through the domain hierarchy when the required scope is not
supported by this domain.  This is the same approach as for filesystem
and network restrictions.

Cc: Günther Noack <[email protected]>
Cc: Mikhail Ivanov <[email protected]>
Cc: Tahera Fahimi <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Mickaël Salaün <[email protected]>

security/landlock/task.c

@@ -204,12 +204,22 @@ static bool is_abstract_socket(struct sock *const sock)
 	return false;
 }
 
+static const struct landlock_ruleset *get_current_unix_scope_domain(void)
+{
+	const union access_masks unix_scope = {
+		.scope = LANDLOCK_SCOPE_ABSTRACT_UNIX_SOCKET,
+	};
+
+	return landlock_match_ruleset(landlock_get_current_domain(),
+				      unix_scope);
+}
+
 static int hook_unix_stream_connect(struct sock *const sock,
 				    struct sock *const other,
 				    struct sock *const newsk)
 {
 	const struct landlock_ruleset *const dom =
-		landlock_get_current_domain();
+		get_current_unix_scope_domain();
 
 	/* Quick return for non-landlocked tasks. */
 	if (!dom)
@@ -225,7 +235,7 @@ static int hook_unix_may_send(struct socket *const sock,
 			      struct socket *const other)
 {
 	const struct landlock_ruleset *const dom =
-		landlock_get_current_domain();
+		get_current_unix_scope_domain();
 
 	if (!dom)
 		return 0;
@@ -243,6 +253,10 @@ static int hook_unix_may_send(struct socket *const sock,
 	return 0;
 }
 
+static const union access_masks signal_scope = {
+	.scope = LANDLOCK_SCOPE_SIGNAL,
+};
+
 static int hook_task_kill(struct task_struct *const p,
 			  struct kernel_siginfo *const info, const int sig,
 			  const struct cred *const cred)
@@ -256,6 +270,7 @@ static int hook_task_kill(struct task_struct *const p,
 	} else {
 		dom = landlock_get_current_domain();
 	}
+	dom = landlock_match_ruleset(dom, signal_scope);
 
 	/* Quick return for non-landlocked tasks. */
 	if (!dom)
@@ -279,7 +294,8 @@ static int hook_file_send_sigiotask(struct task_struct *tsk,
 
 	/* Lock already held by send_sigio() and send_sigurg(). */
 	lockdep_assert_held(&fown->lock);
-	dom = landlock_file(fown->file)->fown_domain;
+	dom = landlock_match_ruleset(landlock_file(fown->file)->fown_domain,
+				     signal_scope);
 
 	/* Quick return for unowned socket. */
 	if (!dom)