linux-kernel - Re: [PATCH] 9p: don't use v9fs_parent_fid() when v9fs_fid

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Message-ID: <1470117018.2665.1.camel@sipsolutions.net>
Date:	Tue, 02 Aug 2016 07:50:18 +0200
From:	Johannes Berg <johannes@...solutions.net>
To:	Al Viro <viro@...IV.linux.org.uk>
Cc:	v9fs-developer@...ts.sourceforge.net, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] 9p: don't use v9fs_parent_fid() when v9fs_fid_clone()
 is needed

On Tue, 2016-08-02 at 01:30 +0100, Al Viro wrote:
> On Mon, Aug 01, 2016 at 09:57:17PM +0200, Johannes Berg wrote:
> > The introduction of v9fs_parent_fid() broke v9fs_vfs_rename()
> > since that doesn't just do v9fs_fid_lookup() but rather uses
> > v9fs_fid_clone() on the ->d_parent.
> > 
> > I suppose it'd be possible to introduce v9fs_clone_parent_fid()
> > but I decided that just reverting the broken change was better
> > for now.
> 
> Sorry for the braino; FWIW, I'd rather add
> 
> static inline struct p9_fid *fid_clone(struct p9_fid *fid)
> {
> 	if (IS_ERR(fid))
> 		return fid;
> 	return p9_client_walk(fid, 0, NULL, 1);
> }
> 
> and turn those into fid_clone(v9fs_parent_fid(old_dentry)), etc.

That would have required much more looking into what happens than I was
about to do :)

>   Has an extra benefit of simplifying several other places.  I'll fix
> and post (with credits to you for spotting the bug in question, of
> course).

No objection, I just did the minimum necessary to make my setup not
crash on use-after-free all the time (thanks to slab debug) :)

Thanks,
johannes