exec: Return ERROR if the executed process could not start

The way hyperstart is designed, when we call into EXECCMD, we always
receive an ACK on the ctl channel, even if the process could not start
as expected. Because of this, the runtime does not raise any error
and terminates returning 0.

But this is wrong because it is expected to get the error not only
from the shim, but from the runtime too.

This bug has been found by running CRI-O bats. Specifically with the
test case "ctr execsync failure" from ctr.bats.

Signed-off-by: Sebastien Boeuf <[email protected]>

Author: Sebastien Boeuf

src/exec.c

@@ -29,7 +29,8 @@ struct stdio_config {
 };
 
 static int hyper_release_exec(struct hyper_exec *);
-static void hyper_exec_process(struct hyper_exec *exec, struct stdio_config *io);
+static void hyper_exec_process(struct hyper_exec *exec, int sync_pipe_fd,
+				struct stdio_config *io);
 
 static int send_exec_finishing(uint64_t seq, int len, int code)
 {
@@ -475,7 +476,8 @@ static int hyper_setup_stdio_events(struct hyper_exec *exec, struct stdio_config
 	return 0;
 }
 
-static int hyper_do_exec_cmd(struct hyper_exec *exec, int pipe, struct stdio_config *io)
+static int hyper_do_exec_cmd(struct hyper_exec *exec, int pipe,
+				int sync_pipe_fd, struct stdio_config *io)
 {
 	struct hyper_container *c;
 
@@ -517,15 +519,18 @@ static int hyper_do_exec_cmd(struct hyper_exec *exec, int pipe, struct stdio_con
 	else
 		unsetenv("TERM");
 
-	hyper_exec_process(exec, io);
+	hyper_exec_process(exec, sync_pipe_fd, io);
 
 out:
 	_exit(125);
 }
 
 // do the exec, no return
-static void hyper_exec_process(struct hyper_exec *exec, struct stdio_config *io)
+static void hyper_exec_process(struct hyper_exec *exec, int sync_pipe_fd,
+				struct stdio_config *io)
 {
+	int ret = 125;
+
 	if (sigprocmask(SIG_SETMASK, &orig_mask, NULL) < 0) {
 		perror("sigprocmask restore mask failed");
 		goto exit;
@@ -561,14 +566,21 @@ static void hyper_exec_process(struct hyper_exec *exec, struct stdio_config *io)
 		 /* the exit codes follow the `chroot` standard,
 		    see docker/docs/reference/run.md#exit-status */
 		if (err == ENOENT)
-			_exit(127);
+			ret = 127;
 		else if (err == EACCES)
-			_exit(126);
+			ret = 126;
+
+		if (sync_pipe_fd >= 0 &&
+		    write(sync_pipe_fd, &ret, sizeof(ret)) != sizeof(ret)) {
+			perror("could not send error code through sync_pipe");
+		}
+
+		_exit(ret);
 	}
 
 exit:
 	fflush(NULL);
-	_exit(125);
+	_exit(ret);
 }
 
 static void hyper_free_exec(struct hyper_exec *exec)
@@ -606,9 +618,24 @@ int hyper_exec_cmd(char *json, int length)
 	return ret;
 }
 
+int hyper_wait_process_start(int fd)
+{
+	int ret = -1;
+
+	if (read(fd, &ret, sizeof(ret)) != sizeof(ret)) {
+		// The other end has been closed because the process has been
+		// properly started.
+		return 0;
+	}
+
+	fprintf(stderr, "error code %d received\n", ret);
+	return ret;
+}
+
 int hyper_run_process(struct hyper_exec *exec)
 {
 	int pipe[2] = {-1, -1};
+	int sync_pipe[2] = {-1, -1};
 	int pid, ret = -1;
 	uint32_t type;
 	struct stdio_config io = {-1, -1,-1, -1,-1, -1};
@@ -634,15 +661,23 @@ int hyper_run_process(struct hyper_exec *exec)
 		goto close_tty;
 	}
 
+	if (pipe2(sync_pipe, O_CLOEXEC) < 0) {
+		perror("create sync_pipe failed");
+		goto close_tty;
+	}
+
 	pid = fork();
 	if (pid < 0) {
 		perror("fork prerequisite process failed");
 		goto close_tty;
 	} else if (pid == 0) {
-		hyper_do_exec_cmd(exec, pipe[1], &io);
+		hyper_do_exec_cmd(exec, pipe[1], sync_pipe[1], &io);
 	}
 	fprintf(stdout, "prerequisite process pid %d\n", pid);
 
+	// Close sync_pipe fd from the parent.
+	close_if_set(sync_pipe[1]);
+
 	if (hyper_get_type(pipe[0], &type) < 0 || (int)type < 0) {
 		fprintf(stderr, "run process failed\n");
 		goto close_tty;
@@ -653,6 +688,11 @@ int hyper_run_process(struct hyper_exec *exec)
 		goto close_tty;
 	}
 
+	if (hyper_wait_process_start(sync_pipe[0])) {
+		fprintf(stderr, "process start failed\n");
+		goto close_tty;
+	}
+
 	exec->pid = type;
 	list_add_tail(&exec->list, &exec->pod->exec_head);
 	exec->ref++;
@@ -668,6 +708,8 @@ int hyper_run_process(struct hyper_exec *exec)
 	if (io.stderrfd >= 0)
 		close(io.stderrfd);
 
+	close(sync_pipe[0]);
+	close(sync_pipe[1]);
 	close(pipe[0]);
 	close(pipe[1]);
 	return ret;