Date: Wed, 30 May 2001 09:38:26 +0100 From: Brian Somers <brian@Awfulhak.org> To: Brian Somers <brian@Awfulhak.org> Cc: freebsd-arch@FreeBSD.org, phk@FreeBSD.org, brian@Awfulhak.org Subject: Re: How to handle cloning in a pseudo device. Message-ID: <200105300838.f4U8cQH31659@hak.lan.Awfulhak.org> In-Reply-To: Message from Brian Somers <brian@Awfulhak.org> of "Wed, 30 May 2001 03:55:52 BST." <200105300255.f4U2tqH13615@hak.lan.Awfulhak.org>
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> Hi,
>
> I've been working on making tun clone properly and have come up with
> a perplexing problem (well, perplexing to me).
>
> As tun currently works, it calls make_dev() from the clone routine.
> If a non-root user does (say) ``touch /dev/tun100'', the clone routine
> is called, /dev/tun100 is make_dev()d with root/wheel/600 permissions
> and the d_open routine is never called because the user doesn't have
> permission to open.
>
> One way to solve this might be to allocate the softc from the clone
> routine, but this means that a rogue user can go into /dev and
> potentially run the system out of memory with a quick ``touch'' loop.
>
> Another way would be to keep a light weight list of make_dev()d-but-
> not-yet-created units. rman springs to mind (8*D), but there's no
> mechanism in rman for retrieving used resources - just for retrieving
> unused ones, and besides, a thoughtful user could touch every even
> numbered tun device and provide the same benefits.
>
> Perhaps the best way is to introduce a failed-to-open EVENTHANDLER
> that'll get called when d_open isn't called for whatever reason.
I guess another alternative is to use dev_depends and depend on a
not-otherwise-used (tunctl?) device.
> Thoughts ?
--
Brian <brian@Awfulhak.org> <brian@[uk.]FreeBSD.org>
<http://www.Awfulhak.org>; <brian@[uk.]OpenBSD.org>
Don't _EVER_ lose your sense of humour !
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