[3/5] security: allow Yama to be unconditionally stacked

diff --git a/include/linux/security.h b/include/linux/security.h
index 8ac20da..8c1d318 100644
--- a/include/linux/security.h
+++ b/include/linux/security.h
@@ -3048,5 +3048,36 @@  static inline void free_secdata(void *secdata)
 { }
 #endif /* CONFIG_SECURITY */
 
+#ifdef CONFIG_SECURITY_YAMA
+extern int yama_ptrace_access_check(struct task_struct *child,
+				    unsigned int mode);
+extern int yama_ptrace_traceme(struct task_struct *parent);
+extern void yama_task_free(struct task_struct *task);
+extern int yama_task_prctl(int option, unsigned long arg2, unsigned long arg3,
+			   unsigned long arg4, unsigned long arg5);
+#else
+static inline int yama_ptrace_access_check(struct task_struct *child,
+					   unsigned int mode)
+{
+	return 0;
+}
+
+static inline int yama_ptrace_traceme(struct task_struct *parent)
+{
+	return 0;
+}
+
+static inline void yama_task_free(struct task_struct *task)
+{
+}
+
+static inline int yama_task_prctl(int option, unsigned long arg2,
+				  unsigned long arg3, unsigned long arg4,
+				  unsigned long arg5)
+{
+	return -ENOSYS;
+}
+#endif /* CONFIG_SECURITY_YAMA */
+
 #endif /* ! __LINUX_SECURITY_H */
 
diff --git a/security/security.c b/security/security.c
index cecd55e..eaafb1a 100644
--- a/security/security.c
+++ b/security/security.c
@@ -152,11 +152,23 @@  int security_binder_transfer_file(struct task_struct *from, struct task_struct *
 
 int security_ptrace_access_check(struct task_struct *child, unsigned int mode)
 {
+#ifdef CONFIG_SECURITY_YAMA_STACKED
+	int rc;
+	rc = yama_ptrace_access_check(child, mode);
+	if (rc)
+		return rc;
+#endif
 	return security_ops->ptrace_access_check(child, mode);
 }
 
 int security_ptrace_traceme(struct task_struct *parent)
 {
+#ifdef CONFIG_SECURITY_YAMA_STACKED
+	int rc;
+	rc = yama_ptrace_traceme(parent);
+	if (rc)
+		return rc;
+#endif
 	return security_ops->ptrace_traceme(parent);
 }
 
@@ -739,6 +751,9 @@  int security_task_create(unsigned long clone_flags)
 
 void security_task_free(struct task_struct *task)
 {
+#ifdef CONFIG_SECURITY_YAMA_STACKED
+	yama_task_free(task);
+#endif
 	security_ops->task_free(task);
 }
 
@@ -854,6 +869,12 @@  int security_task_wait(struct task_struct *p)
 int security_task_prctl(int option, unsigned long arg2, unsigned long arg3,
 			 unsigned long arg4, unsigned long arg5)
 {
+#ifdef CONFIG_SECURITY_YAMA_STACKED
+	int rc;
+	rc = yama_task_prctl(option, arg2, arg3, arg4, arg5);
+	if (rc != -ENOSYS)
+		return rc;
+#endif
 	return security_ops->task_prctl(option, arg2, arg3, arg4, arg5);
 }
 
diff --git a/security/yama/Kconfig b/security/yama/Kconfig
index 51d6709..20ef514 100644
--- a/security/yama/Kconfig
+++ b/security/yama/Kconfig
@@ -11,3 +11,11 @@  config SECURITY_YAMA
 	  Further information can be found in Documentation/security/Yama.txt.
 
 	  If you are unsure how to answer this question, answer N.
+
+config SECURITY_YAMA_STACKED
+	bool "Yama stacked with other LSMs"
+	depends on SECURITY_YAMA
+	default n
+	help
+	  When Yama is built into the kernel, force it to stack with the
+	  selected primary LSM.
diff --git a/security/yama/yama_lsm.c b/security/yama/yama_lsm.c
index 2f7d82b..da219ee 100644
--- a/security/yama/yama_lsm.c
+++ b/security/yama/yama_lsm.c
@@ -100,7 +100,7 @@  static void yama_ptracer_del(struct task_struct *tracer,
  * yama_task_free - check for task_pid to remove from exception list
  * @task: task being removed
  */
-static void yama_task_free(struct task_struct *task)
+void yama_task_free(struct task_struct *task)
 {
 	yama_ptracer_del(task, task);
 }
@@ -116,7 +116,7 @@  static void yama_task_free(struct task_struct *task)
  * Return 0 on success, -ve on error.  -ENOSYS is returned when Yama
  * does not handle the given option.
  */
-static int yama_task_prctl(int option, unsigned long arg2, unsigned long arg3,
+int yama_task_prctl(int option, unsigned long arg2, unsigned long arg3,
 			   unsigned long arg4, unsigned long arg5)
 {
 	int rc;
@@ -243,7 +243,7 @@  static int ptracer_exception_found(struct task_struct *tracer,
  *
  * Returns 0 if following the ptrace is allowed, -ve on error.
  */
-static int yama_ptrace_access_check(struct task_struct *child,
+int yama_ptrace_access_check(struct task_struct *child,
 				    unsigned int mode)
 {
 	int rc;
@@ -296,7 +296,7 @@  static int yama_ptrace_access_check(struct task_struct *child,
  *
  * Returns 0 if following the ptrace is allowed, -ve on error.
  */
-static int yama_ptrace_traceme(struct task_struct *parent)
+int yama_ptrace_traceme(struct task_struct *parent)
 {
 	int rc;
 
@@ -330,6 +330,7 @@  static int yama_ptrace_traceme(struct task_struct *parent)
 	return rc;
 }
 
+#ifndef CONFIG_SECURITY_YAMA_STACKED
 static struct security_operations yama_ops = {
 	.name =			"yama",
 
@@ -338,6 +339,7 @@  static struct security_operations yama_ops = {
 	.task_prctl =		yama_task_prctl,
 	.task_free =		yama_task_free,
 };
+#endif
 
 #ifdef CONFIG_SYSCTL
 static int yama_dointvec_minmax(struct ctl_table *table, int write,
@@ -385,13 +387,17 @@  static struct ctl_table yama_sysctl_table[] = {
 
 static __init int yama_init(void)
 {
+#ifndef CONFIG_SECURITY_YAMA_STACKED
 	if (!security_module_enable(&yama_ops))
 		return 0;
+#endif
 
 	printk(KERN_INFO "Yama: becoming mindful.\n");
 
+#ifndef CONFIG_SECURITY_YAMA_STACKED
 	if (register_security(&yama_ops))
 		panic("Yama: kernel registration failed.\n");
+#endif
 
 #ifdef CONFIG_SYSCTL
 	if (!register_sysctl_paths(yama_sysctl_path, yama_sysctl_table))