uniformly nullify std fds

src/lxc/bdev.c

@@ -227,12 +227,8 @@ static int do_mkfs(const char *path, const char *fstype)
 
 	// If the file is not a block device, we don't want mkfs to ask
 	// us about whether to proceed.
-	close(0);
-	close(1);
-	close(2);
-	open("/dev/zero", O_RDONLY);
-	open("/dev/null", O_RDWR);
-	open("/dev/null", O_RDWR);
+	if (null_stdfds() < 0)
+		exit(1);
 	execlp("mkfs", "mkfs", "-t", fstype, path, NULL);
 	exit(1);
 }

src/lxc/lxccontainer.c

@@ -623,12 +623,10 @@ static bool lxcapi_start(struct lxc_container *c, int useinit, char * const argv
 			return false;
 		}
 		lxc_check_inherited(conf, -1);
-		close(0);
-		close(1);
-		close(2);
-		open("/dev/zero", O_RDONLY);
-		open("/dev/null", O_RDWR);
-		open("/dev/null", O_RDWR);
+		if (null_stdfds() < 0) {
+			ERROR("failed to close fds");
+			return false;
+		}
 		setsid();
 	} else {
 		if (!am_single_threaded()) {
@@ -838,7 +836,7 @@ static char *lxcbasename(char *path)
 	return p;
 }
 
-static bool create_run_template(struct lxc_container *c, char *tpath, bool quiet,
+static bool create_run_template(struct lxc_container *c, char *tpath, bool need_null_stdfds,
 				char *const argv[])
 {
 	pid_t pid;
@@ -860,13 +858,8 @@ static bool create_run_template(struct lxc_container *c, char *tpath, bool quiet
 		char **newargv;
 		struct lxc_conf *conf = c->lxc_conf;
 
-		if (quiet) {
-			close(0);
-			close(1);
-			close(2);
-			open("/dev/zero", O_RDONLY);
-			open("/dev/null", O_RDWR);
-			open("/dev/null", O_RDWR);
+		if (need_null_stdfds && null_stdfds() < 0) {
+			exit(1);
 		}
 
 		src = c->lxc_conf->rootfs.path;

src/lxc/monitor.c

@@ -329,12 +329,8 @@ int lxc_monitord_spawn(const char *lxcpath)
 		exit(EXIT_FAILURE);
 	}
 	lxc_check_inherited(NULL, pipefd[1]);
-	close(0);
-	close(1);
-	close(2);
-	open("/dev/null", O_RDONLY);
-	open("/dev/null", O_RDWR);
-	open("/dev/null", O_RDWR);
+	if (null_stdfds() < 0)
+		exit(EXIT_FAILURE);
 	close(pipefd[0]);
 	sprintf(pipefd_str, "%d", pipefd[1]);
 	execvp(args[0], args);

src/lxc/utils.c

@@ -1122,3 +1122,24 @@ char *get_template_path(const char *t)
 
 	return tpath;
 }
+
+int null_stdfds(void)
+{
+	int fd, ret = -1;
+
+	fd = open("/dev/null", O_RDWR);
+	if (fd < 0)
+		return -1;
+
+	if (dup2(fd, 0) < 0)
+		goto err;
+	if (dup2(fd, 1) < 0)
+		goto err;
+	if (dup2(fd, 2) < 0)
+		goto err;
+
+	ret = 0;
+err:
+	close(fd);
+	return ret;
+}

src/lxc/utils.h

@@ -273,4 +273,5 @@ int detect_shared_rootfs(void);
 int detect_ramfs_rootfs(void);
 char *on_path(char *cmd);
 char *get_template_path(const char *t);
+int null_stdfds(void);
 #endif /* __LXC_UTILS_H */