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/groupmod.c

@@ -59,7 +59,7 @@
 /*
  * Global variables
  */
-const char *Prog;
+static const char Prog[] = "groupmod";
 
 #ifdef	SHADOWGRP
 static bool is_shadow_grp;
@@ -751,10 +751,6 @@ 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);
 
@@ -765,7 +761,7 @@ int main (int argc, char **argv)
 	process_root_flag ("-R", argc, argv);
 	prefix = process_prefix_flag ("-P", argc, argv);
 
-	OPENLOG ("groupmod");
+	OPENLOG (Prog);
 #ifdef WITH_AUDIT
 	audit_help_open ();
 #endif
@@ -791,7 +787,7 @@ int main (int argc, char **argv)
 			exit (E_PAM_USERNAME);
 		}
 
-		retval = pam_start ("groupmod", pampw->pw_name, &conv, &pamh);
+		retval = pam_start (Prog, pampw->pw_name, &conv, &pamh);
 	}
 
 	if (PAM_SUCCESS == retval) {