linux-kernel - Re: [PATCH] configfs: fix a race in configfs

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Date:   Wed, 25 Aug 2021 07:29:00 +0200
From:   Christoph Hellwig <hch@....de>
To:     Al Viro <viro@...iv.linux.org.uk>
Cc:     Christoph Hellwig <hch@....de>,
        "Gong, Sishuai" <sishuai@...due.edu>,
        "jlbec@...lplan.org" <jlbec@...lplan.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] configfs: fix a race in configfs_lookup()

On Wed, Aug 25, 2021 at 05:19:04AM +0000, Al Viro wrote:
> On Mon, Aug 23, 2021 at 07:08:47PM +0200, Christoph Hellwig wrote:
> 
> > We can't hold a spinlock over inode allocation.  So it would have to be
> > something like this:
> 
> Check for -ENAMETOOLONG first; easier for analysis that way.

Indeed.

> > +			dentry->d_fsdata = configfs_get(sd);
> > +			sd->s_dentry = dentry;
> > +			spin_unlock(&configfs_dirent_lock);
> >  
> > -			found = 1;
> > -			err = configfs_attach_attr(sd, dentry);
> > -			break;
> > +			inode = configfs_create(dentry, mode);
> > +			if (IS_ERR(inode)) {
> > +				configfs_put(sd);
> > +				return ERR_CAST(inode);
> 
> Er...  Won't that leave dentry with dangling ->d_fsdata?

Yes.  Existing problem, though.