From ed24d8bc75cfcec12f3e3c39075ec3aa0b715cb4 Mon Sep 17 00:00:00 2001
From: Vincent Penquerc'h <vincent.penquerch@collabora.co.uk>
Date: Mon, 30 Dec 2013 09:17:01 -0500
Subject: [PATCH] qubes-restore: fix race condition in allocating VM IDs

---
 dispvm/qubes-restore.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/dispvm/qubes-restore.c b/dispvm/qubes-restore.c
index 3129d896..038e6f14 100644
--- a/dispvm/qubes-restore.c
+++ b/dispvm/qubes-restore.c
@@ -9,6 +9,7 @@
 #include <unistd.h>
 #include <sys/time.h>
 #include <sys/wait.h>
+#include <sys/file.h>
 #include <syslog.h>
 #include <xs.h>
 
@@ -415,6 +416,10 @@ int get_next_disposable_id()
 		perror("open dispVM.seq");
 		exit(1);
 	}
+	if (flock(fd, LOCK_EX) < 0) {
+		perror("lock dispVM.seq");
+		exit(1);
+	}
 	if (read(fd, &seq, sizeof(seq)) != sizeof(seq)) {
 		perror("read dispVM.seq");
 		exit(1);
@@ -428,6 +433,7 @@ int get_next_disposable_id()
 		perror("write dispVM.seq");
 		exit(1);
 	}
+	flock(fd, LOCK_UN);
 	close(fd);
 	return seq;
 }