Allow nonmatching syscalls to continue normally

This part of the code should never be reached if the kernel is
functioning correctly, but it is better to handle this scenario anyway.

src/bin/seccomp/seccomp_exec.c

@@ -133,6 +133,7 @@ int handle_req(struct seccomp_notif *req,
 	resp->id = req->id;
 	resp->error = -EPERM;
 	resp->val = 0;
+	resp->flags = 0;
 
 #ifndef NDEBUG
 	bool found = false;
@@ -143,9 +144,12 @@ int handle_req(struct seccomp_notif *req,
 	}
 	if (!found) {
 		fprintf(stderr, "huh? trapped system call %d that does not appear on our list?\n", req->data.nr);
-		if (0) {
-			// TODO: Continue the syscall normally if nothing matches
-			resp->flags |= SECCOMP_USER_NOTIF_FLAG_CONTINUE;
+		// allow target to continue the syscall normally
+		resp->flags |= SECCOMP_USER_NOTIF_FLAG_CONTINUE;
+		resp->error = 0;
+		resp->val = 0;
+		if (ioctl(listener, SECCOMP_IOCTL_NOTIF_SEND, resp) < 0 && errno != ENOENT) {
+			perror("ioctl send");
 		}
 		return -1;
 	}

tests/run-tests.sh

@@ -8,7 +8,7 @@ echo "c" > /tmp/c
 gcc tests/tests_general.c -o tests_general
 COPYCAT="/tmp/a /tmp/b" build/copycat -- ./tests_general
 
-gcc -lm tests/benchmark.c -o benchmark
+gcc tests/benchmark.c -lm -o benchmark
 echo -e "\nRunning benchmark without interception:"
 ./benchmark
 echo -e "\nRunning benchmark with interception:"