lib/utmp.c: get_current_utmp(): Use the stack for temporary copies

As Evgeny reported, malloc(3) is overkill here.  He suggested using
other methods, which are less than ideal, but it's true that it's
overkill, and with the stack we can get something readable and more
efficient.

Reported-by: Evgeny Grin (Karlson2k) <[email protected]>
Signed-off-by: Alejandro Colomar <[email protected]>

Author: alejandro-colomar

lib/utmp.c

@@ -158,9 +158,8 @@ get_current_utmp(pid_t main_pid)
 		UT_MATCH_BY_PID_AND_LINE
 	};
 
+	struct utmpx   ut_copy;
 	struct utmpx   *ut;
-	struct utmpx   *ut_by_pid  = NULL;
-	struct utmpx   *ut_by_line = NULL;
 	enum ut_match  match;
 
 	setutxent();
@@ -175,34 +174,27 @@ get_current_utmp(pid_t main_pid)
 		if (main_pid == ut->ut_pid) {
 			if (is_my_tty(ut->ut_line)) {
 				match = UT_MATCH_BY_PID_AND_LINE;
+				ut_copy = *ut;
 				break;
 			}
 
 			if (match < UT_MATCH_BY_PID) {
 				match = UT_MATCH_BY_PID;
-				ut_by_pid = xmalloc_T(1, struct utmpx);
-				*ut_by_pid = *ut;
+				ut_copy = *ut;
 			}
 
 		} else if (   LOGIN_PROCESS == ut->ut_type /* Be more picky when matching by 'ut_line' only */
 			   && is_my_tty(ut->ut_line))
 		{
 			if (match < UT_MATCH_BY_LINE) {
 				match = UT_MATCH_BY_LINE;
-				ut_by_line = xmalloc_T(1, struct utmpx);
-				*ut_by_line = *ut;
+				ut_copy = *ut;
 			}
 		}
 	}
 
-	if (NULL == ut)
-		ut = ut_by_pid ?: ut_by_line;
+	ut = match ? memdup_T(&ut_copy, struct utmpx) : NULL;
 
-	if (NULL != ut)
-		ut = memdup_T(ut, struct utmpx);
-
-	free(ut_by_line);
-	free(ut_by_pid);
 	endutxent();
 
 	return ut;