Merge pull request #45 from hacknix/master

Further work on daemon under Linux.

MMDVMHost.cpp

@@ -39,6 +39,7 @@
 #include <unistd.h>
 #include <signal.h>
 #include <fcntl.h>
+#include <pwd.h>
 #endif
 
 #if defined(_WIN32) || defined(_WIN64)
@@ -134,23 +135,66 @@ int CMMDVMHost::run()
 	if (m_daemon) {
 		// Create new process
 		pid_t pid = ::fork();
-		if (pid == -1)
-			return -1;
+		if (pid == -1) {
+			    ::LogWarning("Couldn't fork() , exiting");
+			    return -1;
+		    }
 		else if (pid != 0)
 			exit(EXIT_SUCCESS);
 
 		// Create new session and process group
-		if (::setsid() == -1)
-			return -1;
+		if (::setsid() == -1){
+			    ::LogWarning("Couldn't setsid(), exiting");
+			    return -1;
+		    }
 
 		// Set the working directory to the root directory
-		if (::chdir("/") == -1)
-			return -1;
+		if (::chdir("/") == -1){
+			    ::LogWarning("Couldn't cd /, exiting");
+			    return -1;
+		    }
 
 		::close(STDIN_FILENO);
 		::close(STDOUT_FILENO);
 		::close(STDERR_FILENO);
+#if !defined(HD44780)
+		//If we are currently root...
+		if (getuid() == 0) {
+		    //get UID for mmdvm user
+		    uid_t mmdvm_uid = getpwnam("mmdvm")->pw_uid;
+		    if (mmdvm_uid == NULL) {
+			    ::LogWarning("Could not get mmdvm UID, exiting");
+			    return -1;
+		    }
+		    //get GID for mmdvm user
+		    gid_t mmdvm_gid = getpwnam("mmdvm")->pw_gid;
+		    if (mmdvm_gid == NULL) {
+			    ::LogWarning("Could not get mmdvm GID, exiting");
+			    return -1;
+		    }
+		    
+		    //Set user and group ID's to mmdvm:mmdvm
+		    if (setgid(mmdvm_gid) != 0) {
+			    ::LogWarning("Could not set mmdvm GID, exiting");
+			    return -1;
+		    }
+		    if (setuid(mmdvm_uid) != 0) {
+			    ::LogWarning("Could not set mmdvm UID, exiting");
+			    return -1;
+		    }
+		    
+		    //Double check it worked (AKA Paranoia) 
+		    if (setuid(0) != -1){
+			    ::LogWarning("It's possible to regain root - something is wrong!, exiting");
+			    return -1;
+		    }
+		
+		}
 	}
+#else
+	::LogWarning("Dropping root permissions in daemon mode is disabled with HD44780 display");
+	}
+#endif
 #endif
 
 	LogInfo(HEADER1);

README.daemon

@@ -0,0 +1,26 @@
+On Linux, to run MMDVMHost as a daemon, set "Daemon=1" in the ini file. 
+
+When this is set, MMDVMHost will attempt to drop privileges to user "mmdvm" and 
+group "mmdvm". If this user and group do not exist on your system, an error 
+will occur and 
+MMDVMHost will not start. 
+
+To add these users, please do the following from the Linux command line:
+
+groupadd mmdvm
+useradd mmdvm -g mmdvm -s /sbin/nologin
+usermod mmdvm -G dialout
+
+Note, without the last line, MMDVMHost will not be able to open the modem. 
+
+Also note, when running as a daemon, STDIN, STDOUT and STDERR are closed, so 
+you must use a logfile to capture logging and the logfile entry in the ini file 
+must be given a full path as MMDVMHost calls "cd /" when daemonising. The same 
+applies to the DMRIds.dat file. 
+
+Also, please note that the code to drop privileges is currently disabled when 
+MMDVMHost is compiled with the HD44780 display as it's currently not possible 
+to use this display as a non-root user.
+
+
+Simon - G7RZU