Re: [PATCH 2/2] NFSv4: Use the net namespace uniquifier if it is set

[Trond Myklebust <trondmy@hammerspace.com>]

On Wed, 2020-10-07 at 17:25 -0400, J. Bruce Fields wrote:
> On Wed, Oct 07, 2020 at 05:07:20PM -0400, trondmy@kernel.org wrote:
> > From: Trond Myklebust <trond.myklebust@hammerspace.com>
> > 
> > If a container sets a net namespace specific uniquifier,
> 
> What you're actually checking is if nn->nfs_client != NULL, and
> that's
> pretty much always true.  (The only time it's NULL is an allocation
> failure in some initialization code, I think.)
> 
> > +	struct nfs_net *nn = net_generic(clp->cl_net, nfs_net_id);
> > +	struct nfs_netns_client *nn_clp = nn->nfs_client;
> > +	const char *id;
> > +	size_t len;
> > +
> >  	buf[0] = '\0';
> > +
> > +	if (nn_clp) {
> 
> Are you sure you don't mean
> 
> 	if (nn_clp->identifier)
> 
> ?
> 
> I think that's how you tell if someone's set it.

We're not holding the rcu_read_lock() here, so there is no point in
dereferencing the identifier pointer. That would cause a toctou race...

> 
> --b.
> 
> > +		rcu_read_lock();
> > +		id = rcu_dereference(nn_clp->identifier);
> > +		if (id && *id != '\0')
> > +			len = strlcpy(buf, id, buflen);
> > +		rcu_read_unlock();
> > +		if (len)
> > +			return len;

Oops. However I do need to ensure that 'len' is always initialised
here.

> > +	}
> > +
> >  	if (nfs4_client_id_uniquifier[0] != '\0')
> >  		return strlcpy(buf, nfs4_client_id_uniquifier, buflen);
> >  	return 0;
> > @@ -6034,7 +6051,7 @@ nfs4_init_nonuniform_client_string(struct
> > nfs_client *clp)
> >  		1;
> >  	rcu_read_unlock();
> >  
> > -	buflen = nfs4_get_uniquifier(buf, sizeof(buf));
> > +	buflen = nfs4_get_uniquifier(clp, buf, sizeof(buf));
> >  	if (buflen)
> >  		len += buflen + 1;
> >  
> > @@ -6081,7 +6098,7 @@ nfs4_init_uniform_client_string(struct
> > nfs_client *clp)
> >  	len = 10 + 10 + 1 + 10 + 1 +
> >  		strlen(clp->cl_rpcclient->cl_nodename) + 1;
> >  
> > -	buflen = nfs4_get_uniquifier(buf, sizeof(buf));
> > +	buflen = nfs4_get_uniquifier(clp, buf, sizeof(buf));
> >  	if (buflen)
> >  		len += buflen + 1;
> >  
> > -- 
> > 2.26.2
-- 
Trond Myklebust
Linux NFS client maintainer, Hammerspace
trond.myklebust@hammerspace.com