linux-kernel - Re: [patch 00/13] vfs: add helpers to check r/o bind mounts

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Date:	Thu, 24 Apr 2008 16:42:52 +0200
From:	Miklos Szeredi <miklos@...redi.hu>
To:	viro@...IV.linux.org.uk
CC:	miklos@...redi.hu, akpm@...ux-foundation.org,
	torvalds@...ux-foundation.org, dave@...ux.vnet.ibm.com,
	ezk@...sunysb.edu, mhalcrow@...ibm.com,
	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [patch 00/13] vfs: add helpers to check r/o bind mounts

> > > And I certainly agree that it ought to be replaced by will/wont pair to
> > > close the remount race.  One that had been there all along.  All fh_verify()
> > > callers of that kind need it - we want to pull mnt_{will,wont}_write()
> > > pair into callers *and* stretch to protect the entire relevant area.
> > > 
> > > Which contains vfs_...() in case of nfsd_create, etc.  See what I mean?
> > > That's exactly the thing I'd been talking about - the area we want to
> > > cover is _bigger_ than vfs_...() and contains nfsd-specific logic.  IOW,
> > > doesn't get folded into any VFS-provided helper.
> > 
> > I still don't get it why it needs to cover nfsd-specifi logic.  What
> > does nfsd have to do with r/o mounts?
> 
> Explain to me again, how fh_verify() manages to contain no nfsd-specific
> logics.  Please.

I didn't say it doesn't contain nfsd specifics.  What I said, that it
doesn't modify the filesystem.  So there's no reason to cover it with
mnt_want_write()/drop_write().

>  You are right - we do have races there.  Always had.
> And nfsd_permission() is the next target for continuation of ro-bind
> series.  Assuming that we don't simply make r/w export to hold will_write
> all along, in which case all these checks around calls of vfs_...() in
> there simply go away - that's also an arguable option.

Yes.  And that _still_ doesn't make the path_*() interface wrong.

Miklos
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