Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!jsq
From: karish@mindcraft.com (Chuck Karish)
Newsgroups: comp.std.unix
Subject: Re: Retaining file permissions
Summary: Changing set-user-id bit on write
Message-ID: <18349@cs.utexas.edu>
Date: 5 Mar 91 23:46:58 GMT
References: <6039@ptsfa.PacBell.COM> <1991Feb22.041826.201@athena.mit.edu> <1991Feb23.234242.812@am.sublink.org> <1991Feb26.153931.27251@athena.mit.edu> <18296@cs.utexas.edu>
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Submitted-by: karish@mindcraft.com (Chuck Karish)

In article <18296@cs.utexas.edu> alex@am.sublink.org (Alex Martelli) writes:
>So, what DOES Posix say about this (open(), write(),
>cat, shell redirection, and permission bits), and what SHOULD it say?

POSIX.1 clause 5.6.1.2, descriptions of S_ISUID and S_ISGID bits:  "On
a regular file, this bit should be cleared on any write."

Note the word "should".  This is a recommendation to implementors, not
a requirement.

BSD 4.3 write(2) man page: "If the real user is not the super-user,
then write() clears the set-user-id bit on a file."

Interactive man pages for stat(2), write(2), and chmod(2) are silent on
this issue.

POSIX.2 is pretty much constrained to accept as valid behavior that's
allowed/suggested by POSIX.1.  I don't think there are any requirements
that the utilities second-guess and defeat the file access policies
that could legitimately be imposed by an underlying POSIX.1 operating
system.

	Chuck Karish		karish@mindcraft.com
	Mindcraft, Inc.		(415) 323-9000

Volume-Number: Volume 22, Number 140