tomoyo: Add a kernel config option for fuzzing testing.

syzbot is reporting kernel panic triggered by memory allocation fault
injection before loading TOMOYO's policy [1]. To make the fuzzing tests
useful, we need to assign a profile other than "disabled" (no-op) mode.
Therefore, let's allow syzbot to load TOMOYO's built-in policy for
"learning" mode using a kernel config option. This option must not be
enabled for kernels built for production system, for this option also
disables domain/program checks when modifying policy configuration via
/sys/kernel/security/tomoyo/ interface.

[1] https://syzkaller.appspot.com/bug?extid=29569ed06425fcf67a95Reported-by: syzbot <syzbot+e1b8084e532b6ee7afab@syzkaller.appspotmail.com>
Reported-by: syzbot <syzbot+29569ed06425fcf67a95@syzkaller.appspotmail.com>
Reported-by: syzbot <syzbot+2ee3f8974c2e7dc69feb@syzkaller.appspotmail.com>
Signed-off-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Signed-off-by: James Morris <jamorris@linux.microsoft.com>

security/tomoyo/Kconfig

@@ -74,3 +74,13 @@ config SECURITY_TOMOYO_ACTIVATION_TRIGGER
 	  You can override this setting via TOMOYO_trigger= kernel command line
 	  option. For example, if you pass init=/bin/systemd option, you may
 	  want to also pass TOMOYO_trigger=/bin/systemd option.
+
+config SECURITY_TOMOYO_INSECURE_BUILTIN_SETTING
+	bool "Use insecure built-in settings for fuzzing tests."
+	default n
+	depends on SECURITY_TOMOYO
+	select SECURITY_TOMOYO_OMIT_USERSPACE_LOADER
+	help
+	  Enabling this option forces minimal built-in policy and disables
+	  domain/program checks for run-time policy modifications. Please enable
+	  this option only if this kernel is built for doing fuzzing tests.

security/tomoyo/common.c

@@ -940,7 +940,7 @@ static bool tomoyo_manager(void)
 	const char *exe;
 	const struct task_struct *task = current;
 	const struct tomoyo_path_info *domainname = tomoyo_domain()->domainname;
-	bool found = false;
+	bool found = IS_ENABLED(CONFIG_SECURITY_TOMOYO_INSECURE_BUILTIN_SETTING);
 
 	if (!tomoyo_policy_loaded)
 		return true;
@@ -2810,6 +2810,16 @@ void tomoyo_check_profile(void)
  */
 void __init tomoyo_load_builtin_policy(void)
 {
+#ifdef CONFIG_SECURITY_TOMOYO_INSECURE_BUILTIN_SETTING
+	static char tomoyo_builtin_profile[] __initdata =
+		"PROFILE_VERSION=20150505\n"
+		"0-CONFIG={ mode=learning grant_log=no reject_log=yes }\n";
+	static char tomoyo_builtin_exception_policy[] __initdata =
+		"aggregator proc:/self/exe /proc/self/exe\n";
+	static char tomoyo_builtin_domain_policy[] __initdata = "";
+	static char tomoyo_builtin_manager[] __initdata = "";
+	static char tomoyo_builtin_stat[] __initdata = "";
+#else
 	/*
 	 * This include file is manually created and contains built-in policy
 	 * named "tomoyo_builtin_profile", "tomoyo_builtin_exception_policy",
@@ -2817,6 +2827,7 @@ void __init tomoyo_load_builtin_policy(void)
 	 * "tomoyo_builtin_stat" in the form of "static char [] __initdata".
 	 */
 #include "builtin-policy.h"
+#endif
 	u8 i;
 	const int idx = tomoyo_read_lock();