Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!ames!xanth!kremer
From: kremer@cs.odu.edu (Lloyd Kremer)
Newsgroups: comp.unix.wizards
Subject: Re: lpr output filters
Summary: isatty() is not the whole solution
Message-ID: <8402@xanth.cs.odu.edu>
Date: 10 Apr 89 19:02:16 GMT
References: <1158@novavax.UUCP>
Distribution: usa
Organization: Old Dominion University, Norfolk, Va.
Lines: 41



In article <8185@chinet.chi.il.us> les@chinet.chi.il.us (Leslie Mikesell)
writes:

>*In article <1159@novavax.UUCP> gls@novavax.UUCP (Gary Schaps) writes:
>*>> > Does it seem reasonable to try to create an lpr output filter which 
>*>> > selectively prevents certain files from being printed?
>*
>*>I would like to "protect" certain files by making them "view only". 
>
>...................................  The best you could do would be
>to make the files unreadable by normal users and provide a setuid program
>that displays the contents only if the output is directly to a terminal.

Even this can be tricky to get right in all cases.  I just ran this program
on our AT&T 3B2 running UNIX(tm) System V Release 3:

	#include <fcntl.h>

	main()
	{
		int fd;

		if((fd = open("/dev/tty15", O_WRONLY)) != -1){
			printf("isatty() returns %d\n", isatty(fd));
			close(fd);
		}
		return(0);
	}

It produced:

	isatty() returns 1

On our system, /dev/tty15 is a NEC Pinwriter P2 parallel printer.
Not all "ttys" are real terminals.

					Lloyd Kremer
					Brooks Financial Systems
					{uunet,sun,...}!xanth!brooks!lloyd