Limit the number of simultanious children

Make sure minidlna cannot fork more than 5 children, to avoid becoming a
fork bomb.

Reported-by: Rinat Ibragimov <ibragimovrinat@mail.ru>

process.c

@@ -0,0 +1,146 @@
+/* Process handling
+ *
+ * Copyright © 2006, Thomas Bernard
+ * Copyright © 2013, Benoît Knecht <benoit.knecht@fsfe.org>
+ *
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *     * Redistributions of source code must retain the above copyright
+ *       notice, this list of conditions and the following disclaimer.
+ *     * Redistributions in binary form must reproduce the above copyright
+ *       notice, this list of conditions and the following disclaimer in the
+ *       documentation and/or other materials provided with the distribution.
+ *     * The name of the author may not be used to endorse or promote products
+ *       derived from this software without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
+ * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
+ * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
+ * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
+ * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
+ * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
+ * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
+ * POSSIBILITY OF SUCH DAMAGE.
+ */
+#include <sys/types.h>
+#include <sys/stat.h>
+#include <unistd.h>
+#include <fcntl.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <errno.h>
+#include <string.h>
+#include <signal.h>
+#include <sys/wait.h>
+
+#include "process.h"
+#include "config.h"
+#include "log.h"
+
+static const int max_number_of_children = 5;
+static int number_of_children = 0;
+
+pid_t
+process_fork(void)
+{
+	if (number_of_children >= max_number_of_children)
+	{
+		errno = EAGAIN;
+		return -1;
+	}
+
+	pid_t pid = fork();
+	if (pid > 0)
+		++number_of_children;
+	return pid;
+}
+
+void
+process_handle_child_termination(int signal)
+{
+	waitpid(-1, NULL, WNOHANG);
+	--number_of_children;
+}
+
+int
+process_daemonize(void)
+{
+	int pid;
+#ifndef USE_DAEMON
+	int i;
+
+	switch(process_fork())
+	{
+		/* fork error */
+		case -1:
+			perror("fork()");
+			exit(1);
+
+		/* child process */
+		case 0:
+		/* obtain a new process group */
+			if( (pid = setsid()) < 0)
+			{
+				perror("setsid()");
+				exit(1);
+			}
+
+			/* close all descriptors */
+			for (i=getdtablesize();i>=0;--i) close(i);		
+
+			i = open("/dev/null",O_RDWR); /* open stdin */
+			dup(i); /* stdout */
+			dup(i); /* stderr */
+
+			umask(027);
+			chdir("/");
+
+			break;
+		/* parent process */
+		default:
+			exit(0);
+	}
+#else
+	if( daemon(0, 0) < 0 )
+		perror("daemon()");
+	pid = getpid();
+#endif
+	return pid;
+}
+
+int
+process_check_if_running(const char *fname)
+{
+	char buffer[64];
+	int pidfile;
+	pid_t pid;
+
+	if(!fname || *fname == '\0')
+		return -1;
+
+	if( (pidfile = open(fname, O_RDONLY)) < 0)
+		return 0;
+
+	memset(buffer, 0, 64);
+
+	if(read(pidfile, buffer, 63))
+	{
+		if( (pid = atol(buffer)) > 0)
+		{
+			if(!kill(pid, 0))
+			{
+				close(pidfile);
+				return -2;
+			}
+		}
+	}
+
+	close(pidfile);
+
+	return 0;
+}