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

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Message-ID: <20080424144448.GH15214@ZenIV.linux.org.uk>
Date:	Thu, 24 Apr 2008 15:44:48 +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 04:36:38PM +0200, Miklos Szeredi wrote:
> > RTFS.  permission() doesn't do "is that vfsmount read-only" checks, exactly
> > because it's 100% bogus - either you cover it with entire area where we
> > are guaranteed to stay r/w, or it's by definition racy.
> 
> I know that.
> 
> That does not mean, that fh_verify() needs to do vfsmount r/o checks.
> AFAICS it's perfectly OK to do that later, around the vfs_ call.

... and around everything else that happens to be done after fh_verify
for write access, surely?  Note that e.g. nfsd_setattr() does _not_ call
vfs_<anything>()...

BTW, that assumes we want to do these checks for nfsd at access time.
And not go for _exports_ being r/w or r/o, with protection applying to
the entire lifetime of export.
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