Re: [PATCH] nfsd: drop the nfsd_put helper

[Jeff Layton]

On Wed, 2024-01-03 at 09:48 -0500, Chuck Lever wrote:
> On Wed, Jan 03, 2024 at 08:36:52AM -0500, Jeff Layton wrote:
> > It's not safe to call nfsd_put once nfsd_last_thread has been called, as
> > that function will zero out the nn->nfsd_serv pointer.
> > 
> > Drop the nfsd_put helper altogether and open-code the svc_put in its
> > callers instead. That allows us to not be reliant on the value of that
> > pointer when handling an error.
> > 
> > Fixes: 2a501f55cd64 ("nfsd: call nfsd_last_thread() before final nfsd_put()")
> > Reported-by: Zhi Li <yieli@xxxxxxxxxx>
> > Cc: NeilBrown <neilb@xxxxxxx>
> > Signed-off-by: Jeffrey Layton <jlayton@xxxxxxxxxx>
> > ---
> > I know it's late, but it would be good to get this into v6.7 if
> > possible. I think it's fairly straightforward.
> 
> How is Zhi finding these? Are there administrative API tests that
> can be shared with the community (say, by adding them to kdevops)?
> 
> 

I wish I knew. In most of these, we see these messages ahead of the
KASAN pops that he's reporting:

[  643.617739] NFSD: Using UMH upcall client tracking operations. 
[  643.617755] NFSD: starting 90-second grace period (net f0000000) 
[  643.780487] svc: failed to register nfsdv3 RPC service (errno 512). 
[  643.780928] svc: failed to register nfsaclv3 RPC service (errno 512). 
[  643.794625] ================================================================== 
[  643.794635] BUG: KASAN: null-ptr-deref in __write_ports_addfd+0x3b9/0x6c0 [nfsd] 
[  643.794779] Write of size 4 at addr 0000000000000058 by task rpc.nfsd/16702 
[  643.794783]  

...

The errno 512 makes me suspect that the rpcbind registration attempt is
catching a signal, and that failure then bubbles up when we're trying to
start the server. I've not been able to reproduce this myself though.


> > ---
> >  fs/nfsd/nfsctl.c | 31 +++++++++++++++++--------------
> >  fs/nfsd/nfsd.h   |  7 -------
> >  2 files changed, 17 insertions(+), 21 deletions(-)
> > 
> > diff --git a/fs/nfsd/nfsctl.c b/fs/nfsd/nfsctl.c
> > index 7cd513e59305..87fed75808ff 100644
> > --- a/fs/nfsd/nfsctl.c
> > +++ b/fs/nfsd/nfsctl.c
> > @@ -693,6 +693,7 @@ static ssize_t __write_ports_addfd(char *buf, struct net *net, const struct cred
> >  	char *mesg = buf;
> >  	int fd, err;
> >  	struct nfsd_net *nn = net_generic(net, nfsd_net_id);
> > +	struct svc_serv *serv;
> >  
> >  	err = get_int(&mesg, &fd);
> >  	if (err != 0 || fd < 0)
> > @@ -703,15 +704,15 @@ static ssize_t __write_ports_addfd(char *buf, struct net *net, const struct cred
> >  	if (err != 0)
> >  		return err;
> >  
> > -	err = svc_addsock(nn->nfsd_serv, net, fd, buf, SIMPLE_TRANSACTION_LIMIT, cred);
> > +	serv = nn->nfsd_serv;
> > +	err = svc_addsock(serv, net, fd, buf, SIMPLE_TRANSACTION_LIMIT, cred);
> >  
> > -	if (err < 0 && !nn->nfsd_serv->sv_nrthreads && !nn->keep_active)
> > +	if (err < 0 && !serv->sv_nrthreads && !nn->keep_active)
> >  		nfsd_last_thread(net);
> > -	else if (err >= 0 &&
> > -		 !nn->nfsd_serv->sv_nrthreads && !xchg(&nn->keep_active, 1))
> > -		svc_get(nn->nfsd_serv);
> > +	else if (err >= 0 && !serv->sv_nrthreads && !xchg(&nn->keep_active, 1))
> > +		svc_get(serv);
> >  
> > -	nfsd_put(net);
> > +	svc_put(serv);
> >  	return err;
> >  }
> >  
> > @@ -725,6 +726,7 @@ static ssize_t __write_ports_addxprt(char *buf, struct net *net, const struct cr
> >  	struct svc_xprt *xprt;
> >  	int port, err;
> >  	struct nfsd_net *nn = net_generic(net, nfsd_net_id);
> > +	struct svc_serv *serv;
> >  
> >  	if (sscanf(buf, "%15s %5u", transport, &port) != 2)
> >  		return -EINVAL;
> > @@ -737,32 +739,33 @@ static ssize_t __write_ports_addxprt(char *buf, struct net *net, const struct cr
> >  	if (err != 0)
> >  		return err;
> >  
> > -	err = svc_xprt_create(nn->nfsd_serv, transport, net,
> > +	serv = nn->nfsd_serv;
> > +	err = svc_xprt_create(serv, transport, net,
> >  			      PF_INET, port, SVC_SOCK_ANONYMOUS, cred);
> >  	if (err < 0)
> >  		goto out_err;
> >  
> > -	err = svc_xprt_create(nn->nfsd_serv, transport, net,
> > +	err = svc_xprt_create(serv, transport, net,
> >  			      PF_INET6, port, SVC_SOCK_ANONYMOUS, cred);
> >  	if (err < 0 && err != -EAFNOSUPPORT)
> >  		goto out_close;
> >  
> > -	if (!nn->nfsd_serv->sv_nrthreads && !xchg(&nn->keep_active, 1))
> > -		svc_get(nn->nfsd_serv);
> > +	if (!serv->sv_nrthreads && !xchg(&nn->keep_active, 1))
> > +		svc_get(serv);
> >  
> > -	nfsd_put(net);
> > +	svc_put(serv);
> >  	return 0;
> >  out_close:
> > -	xprt = svc_find_xprt(nn->nfsd_serv, transport, net, PF_INET, port);
> > +	xprt = svc_find_xprt(serv, transport, net, PF_INET, port);
> >  	if (xprt != NULL) {
> >  		svc_xprt_close(xprt);
> >  		svc_xprt_put(xprt);
> >  	}
> >  out_err:
> > -	if (!nn->nfsd_serv->sv_nrthreads && !nn->keep_active)
> > +	if (!serv->sv_nrthreads && !nn->keep_active)
> >  		nfsd_last_thread(net);
> >  
> > -	nfsd_put(net);
> > +	svc_put(serv);
> >  	return err;
> >  }
> >  
> > diff --git a/fs/nfsd/nfsd.h b/fs/nfsd/nfsd.h
> > index 3286ffacbc56..9ed0e08d16c2 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 {
> > 
> > ---
> > base-commit: 610a9b8f49fbcf1100716370d3b5f6f884a2835a
> > change-id: 20240103-nfsd-fixes-1f1196134a11
> > 
> > Best regards,
> > -- 
> > Jeff Layton <jlayton@xxxxxxxxxx>
> > 
> 

-- 
Jeff Layton <jlayton@xxxxxxxxxx>