seccomp: split mode setting routines

Separates the two mode setting paths to make things more readable with
fewer #ifdefs within function bodies.
Signed-off-by: Kees Cook <keescook@chromium.org>
Reviewed-by: Oleg Nesterov <oleg@redhat.com>
Reviewed-by: Andy Lutomirski <luto@amacapital.net>

kernel/seccomp.c

@@ -489,48 +489,66 @@ long prctl_get_seccomp(void)
 }
 
 /**
- * seccomp_set_mode: internal function for setting seccomp mode
- * @seccomp_mode: requested mode to use
- * @filter: optional struct sock_fprog for use with SECCOMP_MODE_FILTER
- *
- * This function may be called repeatedly with a @seccomp_mode of
- * SECCOMP_MODE_FILTER to install additional filters.  Every filter
- * successfully installed will be evaluated (in reverse order) for each system
- * call the task makes.
+ * seccomp_set_mode_strict: internal function for setting strict seccomp
  *
  * Once current->seccomp.mode is non-zero, it may not be changed.
  *
  * Returns 0 on success or -EINVAL on failure.
  */
-static long seccomp_set_mode(unsigned long seccomp_mode, char __user *filter)
+static long seccomp_set_mode_strict(void)
 {
+	const unsigned long seccomp_mode = SECCOMP_MODE_STRICT;
 	long ret = -EINVAL;
 
 	if (!seccomp_may_assign_mode(seccomp_mode))
 		goto out;
 
-	switch (seccomp_mode) {
-	case SECCOMP_MODE_STRICT:
-		ret = 0;
 #ifdef TIF_NOTSC
-		disable_TSC();
+	disable_TSC();
 #endif
-		break;
+	seccomp_assign_mode(seccomp_mode);
+	ret = 0;
+
+out:
+
+	return ret;
+}
+
 #ifdef CONFIG_SECCOMP_FILTER
-	case SECCOMP_MODE_FILTER:
-		ret = seccomp_attach_user_filter(filter);
-		if (ret)
-			goto out;
-		break;
-#endif
-	default:
+/**
+ * seccomp_set_mode_filter: internal function for setting seccomp filter
+ * @filter: struct sock_fprog containing filter
+ *
+ * This function may be called repeatedly to install additional filters.
+ * Every filter successfully installed will be evaluated (in reverse order)
+ * for each system call the task makes.
+ *
+ * Once current->seccomp.mode is non-zero, it may not be changed.
+ *
+ * Returns 0 on success or -EINVAL on failure.
+ */
+static long seccomp_set_mode_filter(char __user *filter)
+{
+	const unsigned long seccomp_mode = SECCOMP_MODE_FILTER;
+	long ret = -EINVAL;
+
+	if (!seccomp_may_assign_mode(seccomp_mode))
+		goto out;
+
+	ret = seccomp_attach_user_filter(filter);
+	if (ret)
 		goto out;
-	}
 
 	seccomp_assign_mode(seccomp_mode);
 out:
 	return ret;
 }
+#else
+static inline long seccomp_set_mode_filter(char __user *filter)
+{
+	return -EINVAL;
+}
+#endif
 
 /**
  * prctl_set_seccomp: configures current->seccomp.mode
@@ -541,5 +559,12 @@ static long seccomp_set_mode(unsigned long seccomp_mode, char __user *filter)
  */
 long prctl_set_seccomp(unsigned long seccomp_mode, char __user *filter)
 {
-	return seccomp_set_mode(seccomp_mode, filter);
+	switch (seccomp_mode) {
+	case SECCOMP_MODE_STRICT:
+		return seccomp_set_mode_strict();
+	case SECCOMP_MODE_FILTER:
+		return seccomp_set_mode_filter(filter);
+	default:
+		return -EINVAL;
+	}
 }