From mboxrd@z Thu Jan  1 00:00:00 1970
From: Paolo Bonzini <bonzini@gnu.org>
Subject: Re: [PATCH] be paranoid about closed stdin/stdout/stderr
Date: Wed, 27 Aug 2008 10:20:23 +0200
Message-ID: <48B50E47.3010402@gnu.org>
References: <quack.20080825T0128.lthr68djy70@roar.cs.berkeley.edu> <48B28CF8.2060306@viscovery.net> <48B29C52.8040901@gnu.org> <E1KXawS-0001gg-Ty@fencepost.gnu.org> <48B2AFC2.20901@viscovery.net> <7vbpzgb94q.fsf@gitster.siamese.dyndns.org> <E1KXsL9-0004ef-Co@fencepost.gnu.org> <48B3A948.3080800@viscovery.net> <7vsksrad7o.fsf@gitster.siamese.dyndns.org> <48B44C61.2020206@gnu.org> <48B4F5C4.9020404@viscovery.net>
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>> Busybox.  But it runs setuid, as Steven pointed out.
> 
> I straced tee (it was the only tool I found that opens files for writing
> without also opening some for reading). If one of 0,1,2 is closed, it
> *does* dup() the fd that it is going to write.

To be precise, it does a blind "dup2 (fd, 3)" and goes on with file
descriptor 3.

open("foo", O_WRONLY|O_CREAT|O_TRUNC|O_LARGEFILE, 0666) = 0
fcntl64(0, F_DUPFD, 3)                  = 3
close(0)                                = 0

Paolo