Hardcoding Prog to known value

See #959. We now set Prog (program name) based on hardcoded value instead
of argv[0]. This is to help prevent escape sequence injection.

src/userdel.c

@@ -72,7 +72,7 @@
 /*
  * Global variables
  */
-const char *Prog;
+static const char Prog[] = "userdel";
 
 static char *user_name;
 static uid_t user_id;
@@ -959,10 +959,6 @@ int main (int argc, char **argv)
 #endif				/* USE_PAM */
 #endif				/* ACCT_TOOLS_SETUID */
 
-	/*
-	 * Get my name so that I can use it to report errors.
-	 */
-	Prog = Basename (argv[0]);
 	log_set_progname(Prog);
 	log_set_logfd(stderr);
 	(void) setlocale (LC_ALL, "");
@@ -972,7 +968,7 @@ int main (int argc, char **argv)
 	process_root_flag ("-R", argc, argv);
 	prefix = process_prefix_flag ("-P", argc, argv);
 
-	OPENLOG ("userdel");
+	OPENLOG (Prog);
 #ifdef WITH_AUDIT
 	audit_help_open ();
 #endif				/* WITH_AUDIT */
@@ -1056,7 +1052,7 @@ int main (int argc, char **argv)
 			exit (E_PW_UPDATE);
 		}
 
-		retval = pam_start ("userdel", pampw->pw_name, &conv, &pamh);
+		retval = pam_start (Prog, pampw->pw_name, &conv, &pamh);
 	}
 
 	if (PAM_SUCCESS == retval) {