Add landlock07 test

This test is a reproducer for the CVE-2024-42318 bug, also known as
landlock Houdini.

More information at:
https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2024-42318

Reviewed-by: Cyril Hrubis <chrubis@suse.cz>
Signed-off-by: Andrea Cervesato <andrea.cervesato@suse.com>

runtest/syscalls

@@ -706,6 +706,7 @@ landlock03 landlock03
 landlock04 landlock04
 landlock05 landlock05
 landlock06 landlock06
+landlock07 landlock07
 
 lchown01 lchown01
 lchown01_16 lchown01_16

testcases/kernel/syscalls/landlock/.gitignore

@@ -5,3 +5,4 @@ landlock03
 landlock04
 landlock05
 landlock06
+landlock07

testcases/kernel/syscalls/landlock/landlock07.c

@@ -0,0 +1,109 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * Copyright (C) 2024 SUSE LLC Andrea Cervesato <andrea.cervesato@suse.com>
+ */
+
+/**
+ * [Description]
+ *
+ * CVE-2024-42318
+ *
+ * Test to check if system is affected by Landlock Houdini bug:
+ * https://www.suse.com/security/cve/CVE-2024-42318.html
+ *
+ * Kernel bug fixed in:
+ *
+ *  commit 39705a6c29f8a2b93cf5b99528a55366c50014d1
+ *  Author: Jann Horn <jannh@google.com>
+ *  Date:   Wed Jul 24 14:49:01 2024 +0200
+ *
+ *  landlock: Don't lose track of restrictions on cred_transfer
+ */
+
+#include "tst_test.h"
+#include "lapi/prctl.h"
+#include "lapi/keyctl.h"
+#include "tst_test_macros.h"
+#include "landlock_common.h"
+
+static struct landlock_ruleset_attr *ruleset_attr;
+static int ruleset_fd;
+
+static pid_t spawn_houdini(void)
+{
+	pid_t pid;
+
+	SAFE_KEYCTL(KEYCTL_JOIN_SESSION_KEYRING, 0, 0, 0, 0);
+
+	pid = SAFE_FORK();
+	if (!pid) {
+		SAFE_KEYCTL(KEYCTL_JOIN_SESSION_KEYRING, 0, 0, 0, 0);
+		SAFE_KEYCTL(KEYCTL_SESSION_TO_PARENT, 0, 0, 0, 0);
+		exit(0);
+	}
+
+	return pid;
+}
+
+static void run(void)
+{
+	pid_t pid_houdini;
+
+	if (SAFE_FORK())
+		return;
+
+	SAFE_PRCTL(PR_SET_NO_NEW_PRIVS, 1, 0, 0, 0);
+	SAFE_LANDLOCK_RESTRICT_SELF(ruleset_fd, 0);
+
+	TST_EXP_FAIL(open("/dev/null", O_WRONLY), EACCES);
+	if (TST_RET != -1) {
+		SAFE_CLOSE(TST_RET);
+		return;
+	}
+
+	pid_houdini = spawn_houdini();
+	SAFE_WAITPID(pid_houdini, NULL, 0);
+
+	TST_EXP_FAIL(open("/dev/null", O_WRONLY), EACCES);
+	if (TST_RET != -1)
+		SAFE_CLOSE(TST_RET);
+
+	exit(0);
+}
+
+static void setup(void)
+{
+	verify_landlock_is_enabled();
+
+	ruleset_attr->handled_access_fs = LANDLOCK_ACCESS_FS_WRITE_FILE;
+	ruleset_fd = SAFE_LANDLOCK_CREATE_RULESET(
+		ruleset_attr,
+		sizeof(struct landlock_ruleset_attr),
+		0);
+}
+
+static void cleanup(void)
+{
+	if (ruleset_fd != -1)
+		SAFE_CLOSE(ruleset_fd);
+}
+
+static struct tst_test test = {
+	.test_all = run,
+	.setup = setup,
+	.cleanup = cleanup,
+	.forks_child = 1,
+	.bufs = (struct tst_buffers []) {
+		{&ruleset_attr, .size = sizeof(struct landlock_ruleset_attr)},
+		{},
+	},
+	.caps = (struct tst_cap []) {
+		TST_CAP(TST_CAP_REQ, CAP_SYS_ADMIN),
+		{}
+	},
+	.tags = (const struct tst_tag[]) {
+		{"linux-git", "39705a6c29f8"},
+		{"CVE", "2024-42318"},
+		{}
+	}
+};