Merge pull request #16966 from FRRouting/mergify/bp/stable/9.1/pr-16738

lib: Attach stdout to child only if --log=stdout and stdout FD is a tty (backport #16738)

lib/libfrr.c

@@ -1108,9 +1108,12 @@ static void frr_terminal_close(int isexit)
 		 * don't redirect when stdout is set with --log stdout
 		 */
 		for (fd = 2; fd >= 0; fd--)
-			if (isatty(fd) &&
-			    (fd != STDOUT_FILENO || !logging_to_stdout))
+			if (logging_to_stdout && isatty(fd) &&
+			    fd == STDOUT_FILENO) {
+				/* Do nothing. */
+			} else {
 				dup2(nullfd, fd);
+			}
 		close(nullfd);
 	}
 }
@@ -1196,9 +1199,12 @@ void frr_run(struct event_loop *master)
 			 * stdout
 			 */
 			for (fd = 2; fd >= 0; fd--)
-				if (isatty(fd) &&
-				    (fd != STDOUT_FILENO || !logging_to_stdout))
+				if (logging_to_stdout && isatty(fd) &&
+				    fd == STDOUT_FILENO) {
+					/* Do nothing. */
+				} else {
 					dup2(nullfd, fd);
+				}
 			close(nullfd);
 		}