linux-kernel - Re: [PATCH 2/3] fs: namei: Allow follow

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Date:   Thu, 17 Nov 2022 22:12:18 +0100 (CET)
From:   Richard Weinberger <richard@....at>
To:     Jeff Layton <jlayton@...nel.org>
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

----- 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.

> 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.

Thanks,
//richard