Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP
Path: utzoo!mnetor!seismo!rutgers!sri-spam!mordor!lll-tis!ptsfa!hoptoad!academ!killer!jfh
From: jfh@killer.UUCP (John Haugh)
Newsgroups: comp.unix.questions
Subject: Re: access(2) question
Message-ID: <1027@killer.UUCP>
Date: Mon, 22-Jun-87 11:57:02 EDT
Article-I.D.: killer.1027
Posted: Mon Jun 22 11:57:02 1987
Date-Received: Sat, 4-Jul-87 22:27:40 EDT
References: <530@applix.UUCP> <1341@xanth.UUCP>
Organization: The Unix(tm) Connection, Dallas, Texas
Lines: 33
Keywords: access permissions
Summary: But you can't open for execute ...

In article <1341@xanth.UUCP>, john@xanth.UUCP (John Owens) writes:
> In article <530@applix.UUCP>, mark@applix.UUCP (Mark Fox) writes:
> > Does anybody know why access checks file accessibility using the real [ug]id
> > in place of the effective [ug]id? It seems to me that access should agree
> > with open(2) as far as whether a program has write or read access to a file.
> > Inside a set-uid program that assumption obviously doesn't work while
> > uid != euid.
> Well, the reason that access was added was to make it possible for a
> set[ug]id program to be able to discern whether or not the real user
> running it would have access to a certain file.

Access() lets the user specify the type of access they plan on requesting,
and then says wether the user himself would be allowed, regardles of setuid
of setgid privileges.

> > Is there a better way of implementing eaccess than using open/close, assuming
> > I don't have the file already opened?
> 
> Not really.  It doesn't even change the access or update times until
> you do a read or write, respectively, so as long as you don't open
> O_TRUNC or O_CREAT, you'll be ok.

Yes, there is.  You only need use getuid(), geteuid(), stat() in order
to find out if you can access a file.  You only need look at st_mode to
determine if the file is accessible.  Should be fairly simple to write,
just three if-then-else's aught to do it.

- John.

Disclaimer:
	No disclaimer.  Whatcha gonna do, sue me?

"It's never too late to have a happy childhood"