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Message-ID: <29d007755c6066552ac2a1b5bc498ce1ce28ab3b.camel@kernel.org>
Date: Thu, 17 Nov 2022 16:42:30 -0500
From: Jeff Layton <jlayton@...nel.org>
To: Richard Weinberger <richard@....at>
Cc: linux-nfs <linux-nfs@...r.kernel.org>,
linux-kernel <linux-kernel@...r.kernel.org>,
linux-fsdevel <linux-fsdevel@...r.kernel.org>,
chuck lever <chuck.lever@...cle.com>, anna@...nel.org,
trond myklebust <trond.myklebust@...merspace.com>,
Al Viro <viro@...iv.linux.org.uk>, raven@...maw.net,
chris chilvers <chris.chilvers@...sbroker.com>,
david young <david.young@...sbroker.com>,
luis turcitu <luis.turcitu@...sbroker.com>,
david <david@...ma-star.at>
Subject: Re: [PATCH 2/3] fs: namei: Allow follow_down() to uncover auto
mounts
On Thu, 2022-11-17 at 22:12 +0100, Richard Weinberger wrote:
> ----- Ursprüngliche Mail -----
> > Von: "Jeff Layton" <jlayton@...nel.org>
> > What happens when CROSSMOUNT isn't enabled and someone tries to stroll
> > into an automount point? I'm guessing the automount happens but the
> > export is denied?
>
> Exactly.
>
> On the other hand, why should knfsd not trigger automounts?
> Almost any userspace interaction would also do so.
>
I have no issue with knfsd activity triggering an automount, but I think
it'd be best if we don't do that when knfsd can't do anything with the
resulting filesystem. Automounts can be expensive.
> > It seems like LOOKUP_AUTOMOUNT ought to be conditional
> > on the parent export having CROSSMOUNT set.
> >
> > There's also another caller of follow_down too, the UNIX98 pty code.
> > This may be harmless for it, but it'd be best not to perturb that if we
> > can help it.
> >
> > Maybe follow_down can grow a lookupflags argument?
>
> So, in nfsd_cross_mnt() the follow_down() helper should use LOOKUP_AUTOMOUNT only
> if exp->ex_flags & NFSEXP_CROSSMOUNT is true?
> Sounds sane, thanks for the pointer.
>
Yeah, I think so. I do wonder if we ought to make any provision for
"nohide" exports, but since you have to enumerate those explicitly, it
shouldn't be a huge problem for someone to just ensure that they're
mounted beforehand.
--
Jeff Layton <jlayton@...nel.org>
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