--- mtr-0.72/mtr.c.orig	2006-09-29 23:38:49 +0400
+++ mtr-0.72/mtr.c	2006-12-11 02:31:36 +0300
@@ -27,6 +27,10 @@
 #include <sys/socket.h> 
 #include <unistd.h>
 #include <strings.h>
+#include <errno.h>
+#include <error.h>
+#include <pwd.h>
+#include <grp.h>
 
 #include "mtr.h"
 #include "mtr-curses.h"
@@ -114,6 +118,46 @@
   available_options[i] = 0;
 }
 
+static void
+drop_priv(void)
+{
+	uid_t   ruid = getuid();
+
+	if (ruid && geteuid())
+		return;
+
+	if (setgroups(0, NULL) < 0)
+		error(EXIT_FAILURE, errno, "setgroups");
+
+	if (ruid)
+	{
+		if (setgid(getgid()) < 0 || setuid(ruid) < 0)
+			error(EXIT_FAILURE, errno, "setgid/setuid failed");
+	} else
+	{
+		const char *user = "mtruser";
+		struct passwd *pw = getpwnam(user);
+		uid_t uid;
+		gid_t gid;
+
+		if (!pw)
+			error(EXIT_FAILURE, 0,
+			      "lookup of user \"%s\" failed", user);
+		uid = pw->pw_uid;
+		gid = pw->pw_gid;
+		endpwent();
+
+		if (!uid)
+			error(EXIT_FAILURE, 0,
+			      "user \"%s\" should not be root", user);
+
+		if (setgid(gid) < 0 || setuid(uid) < 0)
+			error(EXIT_FAILURE, errno, "setgid/setuid failed");
+	}
+
+	if (chdir("/") < 0)
+		error(EXIT_FAILURE, errno, "chdir");
+}
 
 void parse_arg (int argc, char **argv) 
 {
@@ -330,16 +374,7 @@
   }
 
   /*  Now drop to user permissions  */
-  if (setuid(getuid())) {
-    fprintf (stderr, "mtr: Unable to drop permissions.\n");
-    exit(1);
-  }
-
-  /*  Double check, just in case  */
-  if (geteuid() != getuid()) {
-    fprintf (stderr, "mtr: Unable to drop permissions.\n");
-    exit(1);
-  }
+  drop_priv();
 
   /* reset the random seed */
   srand (getpid());