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

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Message-Id: <E1Jp2Fo-0003sr-BX@pomaz-ex.szeredi.hu>
Date:	Thu, 24 Apr 2008 16:16:52 +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

> > On Thu, Apr 24, 2008 at 03:05:21PM +0200, Miklos Szeredi wrote:
> > > Several calls to nfsd_setattr() for starters.  But I didn't do a full
> > > audit of all vfs_* callers, there might well be others.
> 
> BTW, nfsd_setattr() on r/o ->ex_mnt *will* fail.  Again, check fh_verify()
> and see what it does with MAY_SATTR.

Ahh, nice and racy.  __mnt_is_readonly() is't supposed to be used for
this sort of thing.

> 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?

Miklos
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