Date: Tue, 07 Apr 1998 02:38:44 +0800 From: Peter Wemm <peter@netplex.com.au> To: =?koi8-r?B?4c7E0sXKIP7F0s7P1w==?= <ache@nagual.pp.ru> Cc: committers@FreeBSD.ORG Subject: Re: cvs commit: src/sys/kern vfs_vnops.c src/sys/sys fcntl.h Message-ID: <199804061838.CAA16914@spinner.netplex.com.au> In-Reply-To: Your message of "Mon, 06 Apr 1998 22:16:22 %2B0400." <19980406221622.37671@nagual.pp.ru>
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=?koi8-r?B?4c7E0sXKIP7F0s7P1w==?= wrote:
> > In article <199804061738.KAA02766.kithrup.freebsd.cvs-all@freefall.freebsd.
org> you write:
> > > sys/kern vfs_vnops.c
> > > sys/sys fcntl.h
> > > Log:
> > > Implement a new open(2) flag: O_NOFOLLOW. This will instruct open
> > > to not follow symlinks, but to open a handle on the link itself(!).
> > > As strange as this might sound, it has several useful applications
> > > safe race-free ways of opening files in hostile areas (eg: /tmp, a mode
> > > 1777 /var/mail, etc). It also would allow things like fchown() to work
> > > on the link rather than having to implement a new syscall specifically f
or
> > > that task.
>
>
> If we talk about /tmp links security problem, this change require
> modification of each application, which isn't sounds well. Better hack
> will be to treat 't' bit of directory as 'not follow symlink' instruction
> in the kernel. It autoumatically fix all known /tmp races without
> applications modification.
This has been thrashed out again and again on lists like bugtraq. That
sort of thing is not really a "fix" to the problem - because if the symlink
race is being done under user control (eg: user causing a setuid program
that has a bug), the odds are that it'll use $TMPDIR or something else
silly. Then, the user can mkdir $HOME/tmp, set TMPDIR to $HOME/tmp and do
exactly what they please without any "protection" from 't' bit hacks.
Cheers,
-Peter
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