$NetBSD: patch-check-dup-return-value,v 1.1 2020/04/17 11:28:02 tm Exp $

Check dup() return value. Switched to dup2(), which combines the
close() call.

Richard Laager <rlaager@wiktel.com>
https://sourceforge.net/p/squirrelmail/mailman/message/35526927/

--- src/main.c.orig
+++ src/main.c
@@ -998,6 +998,7 @@
  FILE* fp=NULL;
  pid_t pid;                         /* used just for a fork call */
  int i;
+ int j;
 
     /* detach from our parent if necessary */
     // NOTE: When started under systemd, the parent PID is already 1, so
@@ -1059,9 +1060,15 @@
 		strerror(errno));
 		exit( 1 );
 	}
-	close(2); dup(i);
-	close(1); dup(i);
-	close(0); dup(i);
+	for(j=0; j <= 2; j++)
+	{
+		if (dup2(i, j) < 0)
+		{
+			syslog(LOG_ERR, "%s: dup2() failed: %s", fn,
+				strerror(errno));
+			exit( 1 );
+		}
+	}
 	close(i);
     }
     else