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

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Date:	Thu, 24 Apr 2008 16:12:35 +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 04:53:27PM +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?
>
> What in particular?  You have managed to avoid answering this question
> for the last...I don't know how many emails.

Oh, for fuck sake...  grep and ye shall see.  Right next to setattr we
have nfsd4_set_nfs4_acl(), with pair of set_nfsv4_acl_one().  I'd rather
have those two covered by a single will/wont range, TYVM.

nfsd_create() will happily do vfs_mkdir() and nfsd_create_setattr().  Ditto.

And while we are at it, losing the check for r/o in fh_verify() will sure
as hell require at least handling it separately on the normal write path.

> >  Note that e.g. nfsd_setattr() does _not_ call
> > vfs_<anything>()...
> 
> Yes it does: notify_change().  It's vfs_setattr() under a pseudonym.

Are you going to move the will/wont in there?  Because there's a bunch of
stuff in fs/open.c that will disagree...
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