Re: [PATCH] nfsd: properly tear down server when write_ports fails

[Jeff Layton]

On Tue, 2023-12-12 at 09:59 +1100, NeilBrown wrote:
> On Tue, 12 Dec 2023, Jeff Layton wrote:
> > When the initial write to the "portlist" file fails, we'll currently put
> > the reference to the nn->nfsd_serv, but leave the pointer intact. This
> > leads to a UAF if someone tries to write to "portlist" again.
> > 
> > Simple reproducer, from a host with nfsd shut down:
> > 
> >     # echo "foo 2049" > /proc/fs/nfsd/portlist
> >     # echo "foo 2049" > /proc/fs/nfsd/portlist
> > 
> > The kernel will oops on the second one when it trips over the dangling
> > nn->nfsd_serv pointer. There is a similar bug in __write_ports_addfd.
> > 
> > This patch fixes it by adding some extra logic to nfsd_put to ensure
> > that nfsd_last_thread is called prior to putting the reference when the
> > conditions are right.
> > 
> > Fixes: 9f28a971ee9f ("nfsd: separate nfsd_last_thread() from nfsd_put()")
> > Closes: https://issues.redhat.com/browse/RHEL-19081
> > Reported-by: Zhi Li <yieli@xxxxxxxxxx>
> > Signed-off-by: Jeff Layton <jlayton@xxxxxxxxxx>
> > ---
> > This should probably go to stable, but we'll need to backport for v6.6
> > since older kernels don't have nfsd_nl_rpc_status_get_done. We should
> > just be able to drop that hunk though.
> > ---
> >  fs/nfsd/nfsctl.c | 32 ++++++++++++++++++++++++++++----
> >  fs/nfsd/nfsd.h   |  8 +-------
> >  fs/nfsd/nfssvc.c |  2 +-
> >  3 files changed, 30 insertions(+), 12 deletions(-)
> 
> This is much the same as
> 
> https://lore.kernel.org/linux-nfs/20231030011247.9794-2-neilb@xxxxxxx/
> 
> It seems that didn't land.  Maybe I dropped the ball...
> 
> 

Indeed it is. I thought the problem seemed familiar. Your set is
considerably more comprehensive. Looks like I even sent some Reviewed-
bys when you sent it.

Chuck, can we get these in or was there a problem with them?

Thanks,

> 
> > 
> > diff --git a/fs/nfsd/nfsctl.c b/fs/nfsd/nfsctl.c
> > index 3e15b72f421d..1ceccf804e44 100644
> > --- a/fs/nfsd/nfsctl.c
> > +++ b/fs/nfsd/nfsctl.c
> > @@ -61,6 +61,30 @@ enum {
> >  	NFSD_MaxReserved
> >  };
> >  
> > +/**
> > + * nfsd_put - put the reference to the nfsd_serv for given net
> > + * @net: the net namespace for the serv
> > + * @err: current error for the op
> > + *
> > + * When putting a reference to the nfsd_serv from a control operation
> > + * we must first call nfsd_last_thread if all of these are true:
> > + *
> > + * - the configuration operation is going fail
> > + * - there are no running threads
> > + * - there are no successfully configured ports
> > + *
> > + * Otherwise, just put the serv reference.
> > + */
> > +static inline void nfsd_put(struct net *net, int err)
> > +{
> > +	struct nfsd_net *nn = net_generic(net, nfsd_net_id);
> > +	struct svc_serv *serv = nn->nfsd_serv;
> > +
> > +	if (err < 0 && !nn->nfsd_serv->sv_nrthreads && !nn->keep_active)
> > +		nfsd_last_thread(net);
> > +	svc_put(serv);
> > +}
> > +
> >  /*
> >   * write() for these nodes.
> >   */
> > @@ -709,7 +733,7 @@ static ssize_t __write_ports_addfd(char *buf, struct net *net, const struct cred
> >  	    !nn->nfsd_serv->sv_nrthreads && !xchg(&nn->keep_active, 1))
> >  		svc_get(nn->nfsd_serv);
> >  
> > -	nfsd_put(net);
> > +	nfsd_put(net, err);
> >  	return err;
> >  }
> >  
> > @@ -748,7 +772,7 @@ static ssize_t __write_ports_addxprt(char *buf, struct net *net, const struct cr
> >  	if (!nn->nfsd_serv->sv_nrthreads && !xchg(&nn->keep_active, 1))
> >  		svc_get(nn->nfsd_serv);
> >  
> > -	nfsd_put(net);
> > +	nfsd_put(net, 0);
> >  	return 0;
> >  out_close:
> >  	xprt = svc_find_xprt(nn->nfsd_serv, transport, net, PF_INET, port);
> > @@ -757,7 +781,7 @@ static ssize_t __write_ports_addxprt(char *buf, struct net *net, const struct cr
> >  		svc_xprt_put(xprt);
> >  	}
> >  out_err:
> > -	nfsd_put(net);
> > +	nfsd_put(net, err);
> >  	return err;
> >  }
> >  
> > @@ -1687,7 +1711,7 @@ int nfsd_nl_rpc_status_get_dumpit(struct sk_buff *skb,
> >  int nfsd_nl_rpc_status_get_done(struct netlink_callback *cb)
> >  {
> >  	mutex_lock(&nfsd_mutex);
> > -	nfsd_put(sock_net(cb->skb->sk));
> > +	nfsd_put(sock_net(cb->skb->sk), 0);
> >  	mutex_unlock(&nfsd_mutex);
> >  
> >  	return 0;
> > diff --git a/fs/nfsd/nfsd.h b/fs/nfsd/nfsd.h
> > index f5ff42f41ee7..3aa8cd2c19ac 100644
> > --- a/fs/nfsd/nfsd.h
> > +++ b/fs/nfsd/nfsd.h
> > @@ -113,13 +113,6 @@ int		nfsd_pool_stats_open(struct inode *, struct file *);
> >  int		nfsd_pool_stats_release(struct inode *, struct file *);
> >  void		nfsd_shutdown_threads(struct net *net);
> >  
> > -static inline void nfsd_put(struct net *net)
> > -{
> > -	struct nfsd_net *nn = net_generic(net, nfsd_net_id);
> > -
> > -	svc_put(nn->nfsd_serv);
> > -}
> > -
> >  bool		i_am_nfsd(void);
> >  
> >  struct nfsdfs_client {
> > @@ -153,6 +146,7 @@ struct nfsd_net;
> >  enum vers_op {NFSD_SET, NFSD_CLEAR, NFSD_TEST, NFSD_AVAIL };
> >  int nfsd_vers(struct nfsd_net *nn, int vers, enum vers_op change);
> >  int nfsd_minorversion(struct nfsd_net *nn, u32 minorversion, enum vers_op change);
> > +void nfsd_last_thread(struct net *net);
> >  void nfsd_reset_versions(struct nfsd_net *nn);
> >  int nfsd_create_serv(struct net *net);
> >  
> > diff --git a/fs/nfsd/nfssvc.c b/fs/nfsd/nfssvc.c
> > index fe61d9bbcc1f..d6939e23ffcf 100644
> > --- a/fs/nfsd/nfssvc.c
> > +++ b/fs/nfsd/nfssvc.c
> > @@ -542,7 +542,7 @@ static struct notifier_block nfsd_inet6addr_notifier = {
> >  /* Only used under nfsd_mutex, so this atomic may be overkill: */
> >  static atomic_t nfsd_notifier_refcount = ATOMIC_INIT(0);
> >  
> > -static void nfsd_last_thread(struct net *net)
> > +void nfsd_last_thread(struct net *net)
> >  {
> >  	struct nfsd_net *nn = net_generic(net, nfsd_net_id);
> >  	struct svc_serv *serv = nn->nfsd_serv;
> > 
> > ---
> > base-commit: a39b6ac3781d46ba18193c9dbb2110f31e9bffe9
> > change-id: 20231211-nfsd-fixes-d9f21d5c12d7
> > 
> > Best regards,
> > -- 
> > Jeff Layton <jlayton@xxxxxxxxxx>
> > 
> > 
> 

-- 
Jeff Layton <jlayton@xxxxxxxxxx>