From: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Date: Mon, 4 Jun 2012 22:08:24 +0000 (-0400)
Subject: Fix: close all file descriptors when executed as daemon
X-Git-Tag: v2.1.0-rc1~117
X-Git-Url: https://git.lttng.org./?a=commitdiff_plain;h=ceed52b545103258e84f1c7040700be9dbbbaec6;p=lttng-tools.git

Fix: close all file descriptors when executed as daemon

Both sessiond and consumerd support the option "-d" to run as daemon. In
some specific cases, e.g. when launched from dpkg installation scripts,
file descriptors 3, 4, 5 are left open and don't seem to have O_CLOEXEC
flag set, so the install script hangs because the sessiond still holds a
reference to them. daemon(3) only closes standard FD 0, 1, 2.

Fix this issue by closing all file descriptors after calling daemon(3).
Note: we make sure no file descriptor is opened before calling daemon(3)
by moving the init_thread_quit_pipe() call after the FD close.

Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
---

diff --git a/src/bin/lttng-consumerd/lttng-consumerd.c b/src/bin/lttng-consumerd/lttng-consumerd.c
index 9f2f02feb..3bc700dc9 100644
--- a/src/bin/lttng-consumerd/lttng-consumerd.c
+++ b/src/bin/lttng-consumerd/lttng-consumerd.c
@@ -263,11 +263,26 @@ int main(int argc, char **argv)
 
 	/* Daemonize */
 	if (opt_daemon) {
+		int i;
+
+		/*
+		 * fork
+		 * child: setsid, close FD 0, 1, 2, chdir /
+		 * parent: exit (if fork is successful)
+		 */
 		ret = daemon(0, 0);
 		if (ret < 0) {
-			perror("daemon");
+			PERROR("daemon");
 			goto error;
 		}
+		/*
+		 * We are in the child. Make sure all other file
+		 * descriptors are closed, in case we are called with
+		 * more opened file descriptors than the standard ones.
+		 */
+		for (i = 3; i < sysconf(_SC_OPEN_MAX); i++) {
+			(void) close(i);
+		}
 	}
 
 	if (strlen(command_sock_path) == 0) {
diff --git a/src/bin/lttng-sessiond/main.c b/src/bin/lttng-sessiond/main.c
index e8bd45f15..5cfd57971 100644
--- a/src/bin/lttng-sessiond/main.c
+++ b/src/bin/lttng-sessiond/main.c
@@ -4547,11 +4547,6 @@ int main(int argc, char **argv)
 
 	rcu_register_thread();
 
-	/* Create thread quit pipe */
-	if ((ret = init_thread_quit_pipe()) < 0) {
-		goto error;
-	}
-
 	setup_consumerd_path();
 
 	/* Parse arguments */
@@ -4562,11 +4557,31 @@ int main(int argc, char **argv)
 
 	/* Daemonize */
 	if (opt_daemon) {
+		int i;
+
+		/*
+		 * fork
+		 * child: setsid, close FD 0, 1, 2, chdir /
+		 * parent: exit (if fork is successful)
+		 */
 		ret = daemon(0, 0);
 		if (ret < 0) {
 			PERROR("daemon");
 			goto error;
 		}
+		/*
+		 * We are in the child. Make sure all other file
+		 * descriptors are closed, in case we are called with
+		 * more opened file descriptors than the standard ones.
+		 */
+		for (i = 3; i < sysconf(_SC_OPEN_MAX); i++) {
+			(void) close(i);
+		}
+	}
+
+	/* Create thread quit pipe */
+	if ((ret = init_thread_quit_pipe()) < 0) {
+		goto error;
 	}
 
 	/* Check if daemon is UID = 0 */