fix(switch-root): return real errors instead of a false success

src/api.c

@@ -267,11 +267,12 @@ static void bypass_shutdown(void *unused)
 /*
  * Handle switch_root API command.
  * Parses data: "newroot\0newinit\0"
- * Sends ACK before attempting switch_root since it doesn't return on success.
- * Returns: result from switch_root() on failure, doesn't return on success.
+ * On a precheck failure, sets rq->cmd = INIT_CMD_NACK with a message and returns -1
+ * Returns: result from switch_root_precheck()/switch_root() on failure, doesn't return on success
  */
 static int do_switch_root_api(int sd, struct init_request *rq)
 {
+	char errbuf[sizeof(rq->data)];
 	char *newroot, *newinit = NULL;
 	char *ptr;
 	int result;
@@ -287,8 +288,14 @@ static int do_switch_root_api(int sd, struct init_request *rq)
 			newinit = ptr;
 	}
 
+	if (switch_root_precheck(newroot, newinit, errbuf, sizeof(errbuf))) {
+		rq->cmd = INIT_CMD_NACK;
+		snprintf(rq->data, sizeof(rq->data), "switch-root: %s", errbuf);
+		return -1;
+	}
+
 	/*
-	 * Send ACK first, since we won't return from
+	 * Send ACK now, since we won't return from
 	 * switch_root() on success.
 	 */
 	rq->cmd = INIT_CMD_ACK;
@@ -467,6 +474,7 @@ static void api_cb(uev_t *w, void *arg, int events)
 		case INIT_CMD_SWITCH_ROOT:
 			if (runlevel != INIT_LEVEL && runlevel != 1) {
 				warnx("switch-root only allowed in runlevel S or 1");
+				result = 1;
 				goto done;
 			}
 			break;
@@ -572,8 +580,10 @@ static void api_cb(uev_t *w, void *arg, int events)
 			break;
 
 		case INIT_CMD_SWITCH_ROOT:
-			do_switch_root_api(sd, &rq);
-			goto leave;
+			result = do_switch_root_api(sd, &rq);
+			if (result && rq.cmd == INIT_CMD_NACK)
+				break;	/* precheck failed before ACK, done: sends the NACK */
+			goto leave;	/* success, or a post-ACK failure with sd already closed */
 
 		case INIT_CMD_ACK:
 			dbg("Client failed reading ACK");

src/finit.c

@@ -122,7 +122,7 @@ static void banner(void)
 #endif
 }
 
-static int sulogin(int do_reboot)
+int sulogin(int do_reboot)
 {
 	int rc = EX_OSFILE;
 	char *cmd[] = {

src/initctl.c

@@ -693,10 +693,16 @@ int do_switch_root(int argc, char *argv[])
 	printf(" ...\n");
 
 	/*
-	 * On success, finit exec's new init and we lose connection.
-	 * A "failure" to read reply is actually expected on success.
-	 */
-	client_send(&rq, sizeof(rq));
+	* Nonzero client_send() isn't failure here, unlike do_cmd():
+	* success execs the new init and drops the connection. Only a real NACK means rejection
+	*
+	* Can't distinguish that from finit not running -- dead connect/write also returns nonzero with rq.cmd untouched
+	* Needs client_request() to signal whether anything was sent; every other caller here treats nonzero as failure
+	*/
+	if (client_send(&rq, sizeof(rq)) && rq.cmd == INIT_CMD_NACK) {
+		puts(rq.data);
+		return 1;
+	}
 
 	return 0;
 }
@@ -1414,9 +1420,9 @@ static int show_status(char *arg)
 		snprintf(title, sizeof(title), "%-*s  %-*s  %-8s %-13s ",
 			 pw, "PID", iw, "IDENT", "STATUS", "RUNLEVELS");
 		if (!verbose)
-			strlcat(title, "DESCRIPTION", sizeof(title)); 
+			strlcat(title, "DESCRIPTION", sizeof(title));
 		else
-			strlcat(title, "COMMAND", sizeof(title)); 
+			strlcat(title, "COMMAND", sizeof(title));
 
 		print_header("%s", title);
 	}