linux-kernel - Re: [PATCH 02/11] 9p: fix dentry leak in v9fs_vfs_atomic_open

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Date:	Mon, 16 Sep 2013 20:50:03 +0100
From:	Al Viro <viro@...IV.linux.org.uk>
To:	Miklos Szeredi <miklos@...redi.hu>
Cc:	Linux-Fsdevel <linux-fsdevel@...r.kernel.org>,
	Kernel Mailing List <linux-kernel@...r.kernel.org>,
	"mszeredi@...e.cz" <mszeredi@...e.cz>,
	Eric Van Hensbergen <ericvh@...il.com>,
	"M. Mohan Kumar" <mohan@...ibm.com>, stable@...r.kernel.org
Subject: Re: [PATCH 02/11] 9p: fix dentry leak in v9fs_vfs_atomic_open_dotl()

On Mon, Sep 16, 2013 at 09:03:25PM +0200, Miklos Szeredi wrote:
> On Mon, Sep 16, 2013 at 8:19 PM, Al Viro <viro@...iv.linux.org.uk> wrote:
> > On Mon, Sep 16, 2013 at 02:51:56PM +0200, Miklos Szeredi wrote:
> >> From: Miklos Szeredi <mszeredi@...e.cz>
> >>
> >> commit b6f4bee02f "fs/9p: Fix atomic_open" fixed the O_EXCL behavior, but
> >> results in a dentry leak if v9fs_vfs_lookup() returns non-NULL.
> >
> > Frankly, I would prefer to deal with that in fs/namei.c:atomic_open()
> > instead.  I.e. let it call finish_no_open() as it used to do and
> > turn
> >                 if (create_error && dentry->d_inode == NULL) {
> >                         error = create_error;
> >                         goto out;
> >                 }
> > in fs/namei.c:atomic_open() into
> >                 if (!dentry->d_inode) {
> >                         if (create_error) {
> >                                 error = create_error;
> >                                 goto out;
> >                         }
> >                 } else if ((open_flag & (O_CREAT | O_EXCL)) == (O_CREAT | O_EXCL)) {
> >                         error = -EEXIST;
> >                         goto out;
> >                 }
> >
> > rather than try to deal with that crap in each instance of ->atomic_open()...
> > Objections?
> 
> ->atomic_open() could be any one of
> 
>  lookup
>  lookup+create
>  lookup+create+open
> 
> If it's the second one then the above is wrong.  Sure, we could check
> FILE_CREATED as well, and if file wasn't created yet dentry is
> positive then we return EEXIST.  But for that to be correct we need
> the last patch in the series, preventing FILE_CREATED from being set
> unconditionally.

You mean, lookup + create + return finish_no_open()?  Does anything actually
do that?  I agree that we want your "deal with setting FILE_CREATED in
filesystems", BTW, and I'm fine with putting it in front of the rest of
the queue.

I would definitely prefer EEXIST logics dealt with in fs/namei.c - if nothing
else, it had been done wrong in too many instances...
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