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

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Message-Id: <E1Jp2tc-00044i-6k@pomaz-ex.szeredi.hu>
Date:	Thu, 24 Apr 2008 16:58:00 +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

> > >  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.
> 
> It would make it bloody useless for nfsd.  With ecryptfs being a piss-poor
> argument in favour of anything other than git rm, what's left?  Another
> stack frame in fs/namei.c syscalls?

Since all the vfs_* functions will become static with path_* being the
only caller, the compiler will be happy to get rid of that stack frame
too.

What is left is the guarantee, that the race-free r/o remounts will
always work and some obscure caller didn't forget to surround it with
the r/o checks.

I think it's definitely worth it.

Miklos
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