--- qemu-start/trunk/qemu-start.c	2006/02/11 16:36:13	294
+++ qemu-start/trunk/qemu-start.c	2007/08/10 12:12:28	295
@@ -30,10 +30,199 @@
 #include <stdlib.h>
 #include <net/if.h>
 #include <linux/if_tun.h>
+#include <sys/wait.h>
+#include <errno.h>
+
+/* This define is present in recent glibc, it is not available on sarge */
+#ifndef HOST_NAME_MAX
+#define HOST_NAME_MAX 64
+#endif
 
 #define QEMU "/usr/bin/qemu"
 #define USER "qemu"
 
+/* 
+ * This function merges the xauthority data of the current X context
+ * into the QEMU user's .Xauthority file.
+ */
+void fix_xauthority(void) {
+	struct passwd *userdata;
+	int pfd[2];
+	char *xauthfile;
+	char *display;
+	char *newdisplay;
+	char *hostname;
+//	int status1, status2;
+	int status,pid;
+	pid_t cpid1, cpid2;
+
+	if (pipe(pfd)) {
+		perror("pipe failed");
+		exit(1);
+	}
+
+	cpid1 = fork();
+	if (cpid1 < 0) {
+		perror("first fork failed");
+		exit(1);
+	}
+
+	/* Child: will execute the xauth extract */
+	if (cpid1 == 0) {
+		/* Child may run as original process starter */
+		if (setgroups(0, NULL)) {
+			perror("setgroups failed");
+			exit(1);
+		}
+		if (setgid(getgid())) {
+			perror("setgid failed");
+			exit(1);
+		}
+		if (setuid(getuid())) {
+			perror("setuid failed");
+			exit(1);
+		}
+
+		/* Write side of pipe corresponds to stdout */
+		if (dup2(pfd[1],1) < 0) {
+			perror("dup2 failed");
+			exit(1);
+		}
+		if (close(pfd[0])) {
+			perror("close of pfd[0] failed");
+			exit(1);
+		}
+		if (close(pfd[1])) {
+			perror("close of pfd[1] failed");
+			exit(1);
+		}
+		
+		userdata = getpwuid(getuid());
+		if (!userdata) {
+			fprintf(stderr, "No user '%s'\n", USER);
+			exit(1);
+		}
+
+
+		/* Get xauthority file to use */
+		if (! (xauthfile = getenv("XAUTHORITY"))) {
+			if (asprintf(&xauthfile,"%s/.Xauthority",userdata->pw_dir) < 1) {
+				perror("Constructing xauthority filename failed");
+				exit(1);
+			}
+		}
+
+		/* Get display */
+		if (! (display = getenv("DISPLAY"))) {
+			perror("No DISPLAY variable found\n");
+			exit(1);
+		}
+
+		/* Substitution: if display starts with `localhost', substitute 
+		   `localhost' by `HOSTNAME/unix'. */
+		if (strstr(display,"localhost") == display) {
+			hostname = malloc(HOST_NAME_MAX+1);
+			if (gethostname(hostname,HOST_NAME_MAX+1)) {
+				perror("Getting hostname failed");
+				exit(1);
+			}
+
+			if (!(newdisplay = malloc(strlen(hostname) + 5 + strlen(display)-9 + 1))) {
+				perror("Allocating new display failed");
+				exit(1);
+			}
+			strcpy(newdisplay,hostname);
+			strcpy(newdisplay + strlen(hostname),"/unix");
+			strcpy(newdisplay + strlen(hostname) + 5, display + 9);
+			display = newdisplay;
+		} else if (! (display = strdup(display))) {
+			perror("strdup DISPLAY failed");
+			exit(1);
+		}
+
+		execl("/usr/bin/X11/xauth","/usr/bin/X11/xauth","-f",xauthfile,"extract","-",display,NULL);
+		exit(1);
+	}
+
+
+	cpid2 = fork();
+	if (cpid2 < 0) {
+		perror("second fork failed");
+		exit(1);
+	}
+
+	/* Child: will execute the xauth merge */
+	if (cpid2 == 0) {
+		/* Get userid data. */
+		userdata = getpwnam(USER);
+		if (!userdata) {
+			fprintf(stderr, "No user '%s'\n", USER);
+			exit(1);
+		}
+
+		if (setgroups(0, NULL)) {
+			perror("setgroups failed");
+			exit(1);
+		}
+		 
+		/* Child may run as qemu user */
+		if (setgid(userdata->pw_gid)) {
+			perror("setgid failed");
+			exit(1);
+		}
+		if (setuid(userdata->pw_uid)) {
+			perror("setuid failed");
+			exit(1);
+		}
+		/* Read side of pipe is stdin */
+		if (dup2(pfd[0],0) < 0) {
+			perror("dup2 failed");
+			exit(1);
+		}
+		if (close(pfd[0])) {
+			perror("close of pfd[0] failed");
+			exit(1);
+		}
+		if (close(pfd[1])) {
+			perror("close of pfd[1] failed");
+			exit(1);
+		}
+
+		if (asprintf(&xauthfile,"%s/.Xauthority",userdata->pw_dir) < 1) {
+		  	perror("Constructing xauthority filename failed");
+			exit(1);
+		}
+
+		execl("/usr/bin/X11/xauth","/usr/bin/X11/xauth","-f",xauthfile,"merge","-",NULL);
+		exit(1);
+	}
+
+	if (close(pfd[0])) {
+		perror("close of pfd[0] failed");
+		exit(1);
+	}
+	if (close(pfd[1])) {
+		perror("close of pfd[1] failed");
+		exit(1);
+	}
+
+	while(1) {
+	
+		pid = wait(&status);
+		if ((pid < 1) && (errno == ECHILD))
+			break;
+		if (pid < 1) {
+			perror("wait failed");
+			exit(1);
+		}
+		if (! WIFEXITED(status) || WEXITSTATUS(status)) {
+			fprintf(stderr,"Child returned error");
+			exit(1);
+		}
+	}
+}
+
+
 /* Tiny code to open tap/tun device, and hand the fd to qemu.
    Run as root, drops to given user. */
 int main(int argc, char *argv[])
@@ -43,9 +232,7 @@
 	char *newargs[argc + 2];
 	int i,fd,vlan,tapnr;
 	char *ptr;
-	char *command;
 	char *display;
-	char *xauthfile;
 
 	/* Check parameters */
 	if (argc < 4) {
@@ -60,17 +247,26 @@
 	/* First parameter: TAPDEVNR */
 	tapnr = strtol(argv[1],&ptr,0);
 	if (*ptr) {
-		fprintf(stderr, "Invalid value for TAPDEVNR parameter (use a number!)\n");
+		fprintf(stderr, "Invalid value `%s' for TAPDEVNR parameter (use a number!)\n",argv[1]);
 		exit(1);
 	}
 
 	/* Second parameter: VLAN */
 	vlan = strtol(argv[2],&ptr,0);
 	if (*ptr) {
-		fprintf(stderr, "Invalid value for VLAN parameter (use a number!)\n");
+		fprintf(stderr, "Invalid value `%s' for VLAN parameter (use a number!)\n", argv[2]);
+		exit(1);
+	}
+
+	/* Third parameter: System type */
+	if (index(argv[3],'/')) {
+		fprintf(stderr, "Invalid value `%s' for system (may not contain a slash character)\n", argv[3]);
 		exit(1);
 	}
 
+	/* Export the xauth data */
+	fix_xauthority();
+
 	/* Open /dev/net/tun */
 	fd = open("/dev/net/tun", O_RDWR);
 	if (fd < 0) {
@@ -88,50 +284,67 @@
 		exit(1);
 	}
 
-	/* Fix X-display */
-	userdata = getpwuid(getuid());
-	if (! (xauthfile = getenv("XAUTHORITY")))
-		asprintf(&xauthfile,"~%s/.Xauthority",userdata->pw_name);
-	setuid(0);
-	setgid(0);
-	asprintf(&command,"xauth -f %s extract - $(echo $DISPLAY|sed \"s,^localhost,$(hostname)/unix,\") | xauth -f ~%s/.Xauthority merge -; chown %s: ~%s/.Xauthority",xauthfile,USER,USER,USER);
-fprintf(stderr,"%s\n",command);
-	system(command);
-
-	/* Set correct userid. */
+	/* Get userid data. */
 	userdata = getpwnam(USER);
 	if (!userdata) {
 		fprintf(stderr, "No user '%s'\n", USER);
 		exit(1);
 	}
-	setgroups(0, NULL);
-	setgid(userdata->pw_gid);
-	if (setuid(userdata->pw_uid) != 0) {
-		perror("setting uid");
+
+	/* Change to QEMU user */
+	if (setgroups(0, NULL)) {
+		perror("setgroups failed");
+		exit(1);
+	}
+	if (setgid(userdata->pw_gid)) {
+		perror("setgid failed");
+		exit(1);
+	}
+	if (setuid(userdata->pw_uid)) {
+		perror("setuid failed");
 		exit(1);
 	}
 
 	/* Clean the environment */
-	display=getenv("DISPLAY");
-	clearenv();
-	setenv("HOME",userdata->pw_dir,1);
-	setenv("DISPLAY",display,1);
-	setenv("PATH","/usr/bin:/bin:/usr/local/bin",1);
-	setenv("LOGNAME",userdata->pw_name,1);
-	setenv("USER",userdata->pw_name,1);
+	if(!(display=getenv("DISPLAY"))) {
+		perror("Getting DISPLAY failed");
+		exit(1);
+	}
+	if(clearenv()) {
+		perror("Clearing environment failed");
+		exit(1);
+	}
+	if(setenv("HOME",userdata->pw_dir,1) ||
+	   setenv("DISPLAY",display,1) ||
+	   setenv("PATH","/usr/bin:/bin:/usr/local/bin",1) ||
+	   setenv("LOGNAME",userdata->pw_name,1) ||
+	   setenv("USER",userdata->pw_name,1)) {
+		perror("Setting environment failed");
+		exit(1);
+	}
 
 	/* Create the right qemu invocation */
 	if (!strlen(argv[3]))
 		newargs[0] = QEMU;
-	else
-		asprintf(&newargs[0],"%s-system-%s",QEMU,argv[3]);
+	else if (asprintf(&newargs[0],"%s-system-%s",QEMU,argv[3]) < 0) {
+		perror("Preparing qemu executable filename failed");
+		exit(1);
+	}
 	newargs[1] = "-net";
-	asprintf(&newargs[2],"nic,vlan=%d",vlan);
+	if (asprintf(&newargs[2],"nic,vlan=%d",vlan) < 0) {
+		perror("Preparing nic argument failed");
+		exit(1);
+	}
 	newargs[3] = "-net";
-	asprintf(&newargs[4],"tap,fd=%d,vlan=%d",fd,vlan);
+	if (asprintf(&newargs[4],"tap,fd=%d,vlan=%d",fd,vlan) < 0) {
+		perror("Preparing tap argument failed");
+		exit(1);
+	}
 	for (i = 4; i <= argc; i++)
 		newargs[i+1] = argv[i];
 
 	execvp(newargs[0], newargs);
+	perror('Execution of qemu failed');
 	exit(1);
 }
+