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

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Message-ID: <20080424140000.GE15214@ZenIV.linux.org.uk>
Date:	Thu, 24 Apr 2008 15:00:00 +0100
From:	Al Viro <viro@...IV.linux.org.uk>
To:	Miklos Szeredi <miklos@...redi.hu>
Cc:	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 02:48:26PM +0100, Al Viro wrote:
> 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.

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.
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