commit 0597875b1639e6773eb2cededfeb354befb568c8
Author: Mikolaj Golub <trociny@freebsd.org>
Date:   Thu Feb 9 22:48:28 2012 +0200

    The pidfile_open(3) is going to be fixed to set close-on-exec in order
    not to leak the descriptor after exec(3). This raises the issue for
    daemon(3) of the pidfile lock to be lost when the child process
    executes.
    
    To solve this and also to have the pidfile cleaned up when the program
    exits, if a pidfile is specified, spawn a child to exec the command
    and wait in the parent keeping the pidfile locked until the child
    process exits and remove the file.
    
    Reported by:	Andrey Zonov <andrey zonov org>
    Suggested by:	pjd
    Reviewed by:	pjd
    MFC after:	2 weeks

diff --git a/usr.sbin/daemon/daemon.8 b/usr.sbin/daemon/daemon.8
index d1d4e35..ab85e1d 100644
--- a/usr.sbin/daemon/daemon.8
+++ b/usr.sbin/daemon/daemon.8
@@ -59,14 +59,18 @@ Write the ID of the created process into the
 using the
 .Xr pidfile 3
 functionality.
-If the
+The program is executed in a spawned child process while the
+.Nm
+waits until it terminates to keep the
+.Ar file
+locked and removes it after the process exits.
+The
+.Ar file
+owner is the user who runs the
+.Nm
+regardless of whether the
 .Fl u
-option is used, either the pidfile needs to have been pre-created
-with appropriate ownership and permissions, or the directory to contain
-the pidfile must be writable by the specified user.
-Note, that the file will be created shortly before the process is
-actually executed, and will remain after the process exits (although
-it will be removed if the execution fails).
+option is used or not.
 .It Fl u Ar user
 Login name of the user to execute the program under.
 Requires adequate superuser privileges.
diff --git a/usr.sbin/daemon/daemon.c b/usr.sbin/daemon/daemon.c
index 540ebf3..26c3cb5 100644
--- a/usr.sbin/daemon/daemon.c
+++ b/usr.sbin/daemon/daemon.c
@@ -32,6 +32,7 @@
 __FBSDID("$FreeBSD$");
 
 #include <sys/param.h>
+#include <sys/wait.h>
 
 #include <err.h>
 #include <errno.h>
@@ -43,15 +44,16 @@ __FBSDID("$FreeBSD$");
 #include <unistd.h>
 
 static void restrict_process(const char *);
+static void wait_child(pid_t pid);
 static void usage(void);
 
 int
 main(int argc, char *argv[])
 {
 	struct pidfh *pfh = NULL;
-	int ch, nochdir, noclose, errcode;
+	int ch, nochdir, noclose;
 	const char *pidfile, *user;
-	pid_t otherpid;
+	pid_t otherpid, pid;
 
 	nochdir = noclose = 1;
 	pidfile = user = NULL;
@@ -79,9 +81,7 @@ main(int argc, char *argv[])
 	if (argc == 0)
 		usage();
 
-	if (user != NULL)
-		restrict_process(user);
-
+	pfh = NULL;
 	/*
 	 * Try to open the pidfile before calling daemon(3),
 	 * to be able to report the error intelligently
@@ -100,22 +100,37 @@ main(int argc, char *argv[])
 	if (daemon(nochdir, noclose) == -1)
 		err(1, NULL);
 
-	/* Now that we are the child, write out the pid */
-	if (pidfile)
+	pid = 0;
+	if (pidfile) {
+		/*
+		 * Spawn a child to exec the command, so in the parent
+		 * we could wait for it to exit and remove pidfile.
+		 */
+		pid = fork();
+		if (pid == -1) {
+			pidfile_remove(pfh);
+			err(1, "fork");
+		}
+	}
+	if (pid == 0) {
+		/* Now that we are the child, write out the pid. */
 		pidfile_write(pfh);
 
-	execvp(argv[0], argv);
+		if (user != NULL)
+			restrict_process(user);
 
-	/*
-	 * execvp() failed -- unlink pidfile if any, and
-	 * report the error
-	 */
-	errcode = errno; /* Preserve errcode -- unlink may reset it */
-	if (pidfile)
-		pidfile_remove(pfh);
+		execvp(argv[0], argv);
 
-	/* The child is now running, so the exit status doesn't matter. */
-	errc(1, errcode, "%s", argv[0]);
+		/*
+		 * execvp() failed -- report the error. The child is
+		 * now running, so the exit status doesn't matter.
+		 */
+		err(1, "%s", argv[0]);
+	}
+	setproctitle("%s[%d]", argv[0], pid);
+	wait_child(pid);
+	pidfile_remove(pfh);
+	exit(0); /* Exit status does not matter. */
 }
 
 static void
@@ -132,6 +147,19 @@ restrict_process(const char *user)
 }
 
 static void
+wait_child(pid_t pid)
+{
+	int status;
+
+	while (waitpid(pid, &status, 0) == -1) {
+		if (errno != EINTR) {
+			warn("waitpid");
+			break;
+		}
+	}
+}
+
+static void
 usage(void)
 {
 	(void)fprintf(stderr,