Date: Sat, 6 Jan 2007 08:18:26 -0800 (PST) From: Jon Passki <cykyc@yahoo.com> To: Robert Watson <rwatson@FreeBSD.org>, Colin Percival <cperciva@freebsd.org> Cc: Ceri Davies <ceri@submonkey.net>, "freebsd-arch@freebsd.org" <freebsd-arch@freebsd.org> Subject: Re: default value of security.bsd.hardlink_check_[ug]id Message-ID: <77286.26791.qm@web56107.mail.re3.yahoo.com> In-Reply-To: <20070102230111.M7974@fledge.watson.org>
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--- Robert Watson <rwatson@FreeBSD.org> wrote: > > On Mon, 1 Jan 2007, Colin Percival wrote: > > > Ceri Davies wrote: > >> On Sat, Dec 30, 2006 at 09:08:42PM -0800, Colin Percival wrote: > >>> I'd like to make security.bsd.hardlink_check_[ug]id default to 1, > starting > >>> with FreeBSD 7.x. This would make it impossible for a user to > create a hard > >>> link to a file which he does not own. > >> > >> a) you have provided no rationale; > > > > Allowing users to create hard links to files which they do not own > creates > > problems: > > 1. If disk quotas are enabled, a user can waste another user's disk > quota by > > making it impossible for said other user to delete files. > > 2. It becomes difficult to apply security fixes for issues > involving setuid > > binaries, since a local attacker could create hard links to all the > setuid > > binaries (or at least those on filesystems where he can write > somewhere) and > > wait for a security issue to be found. > > I find the second argument here most compelling, and use it as an > example > frequently when complaining about hard links. Hard links also one of > the > elements that makes it difficult to usefully generate names for file > system > objects, due to their introducing ambiguity. Or this goofy one: http://www.freebsd.org/cgi/query-pr.cgi?pr=conf/89589 Btw, OpenBSD does not allow this behavior but NetBSD does. At a minimum, if the user cannot even copy a file, he or she ought not to hard link the file. This behaviour, though, was permitted the last time I checked. Cheers, Jon __________________________________________________ Do You Yahoo!? Tired of spam? Yahoo! Mail has the best spam protection around http://mail.yahoo.com
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