Re: [PATCH v3 8/8] NFSD: Send CB_OFFLOAD on graceful shutdown

[Jeff Layton <jlayton@kernel.org>]

On Fri, 2024-11-01 at 09:18 -0400, Chuck Lever wrote:
> On Fri, Nov 01, 2024 at 09:05:07AM -0400, Jeff Layton wrote:
> > On Thu, 2024-10-31 at 09:40 -0400, cel@kernel.org wrote:
> > > From: Chuck Lever <chuck.lever@oracle.com>
> > > 
> > > If an async COPY operation happens to be running when the server is
> > > shut down, notify the requesting client that the copy has completed.
> > > 
> > > Since the nfs4_client is going away, seems like this could introduce
> > > some UAFs.
> > > 
> > > Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
> > > ---
> > >  fs/nfsd/nfs4proc.c | 6 +++++-
> > >  1 file changed, 5 insertions(+), 1 deletion(-)
> > > 
> > > diff --git a/fs/nfsd/nfs4proc.c b/fs/nfsd/nfs4proc.c
> > > index 4c964bce6bd7..51b3f85f3791 100644
> > > --- a/fs/nfsd/nfs4proc.c
> > > +++ b/fs/nfsd/nfs4proc.c
> > > @@ -68,6 +68,8 @@ MODULE_PARM_DESC(nfsd4_ssc_umount_timeout,
> > >  
> > >  #define NFSDDBG_FACILITY		NFSDDBG_PROC
> > >  
> > > +static void nfsd4_send_cb_offload(struct nfsd4_copy *copy);
> > > +
> > >  static u32 nfsd_attrmask[] = {
> > >  	NFSD_WRITEABLE_ATTRS_WORD0,
> > >  	NFSD_WRITEABLE_ATTRS_WORD1,
> > > @@ -1381,8 +1383,10 @@ void nfsd4_shutdown_copy(struct nfs4_client *clp)
> > >  {
> > >  	struct nfsd4_copy *copy;
> > >  
> > > -	while ((copy = nfsd4_get_copy(clp)) != NULL)
> > > +	while ((copy = nfsd4_get_copy(clp)) != NULL) {
> > >  		nfsd4_stop_copy(copy);
> > > +		nfsd4_send_cb_offload(copy);
> > > +	}
> > 
> > Not sure about a UAF, but it seems like NFS4ERR_DELAY returns might
> > delay the client destruction for quite a while.
> 
> The nfsd4_copy() is removed from the nfs4_client's async_copies
> list, and the RPC proceeds in the background. It doesn't block the
> destruction of the CLIENTID.
> 
> But it might be a problem for the RPC logic to transmit the call
> when there's no nfs4_client to dereference. I should probably
> drop this patch and try a different approach.


No, I think this will block the client shutdown. After
nfsd4_shutdown_copy(), it calls nfsd4_shutdown_callback(), which does:

        flush_workqueue(clp->cl_callback_wq);                         
        nfsd41_cb_inflight_wait_complete(clp);  

So the CB_OFFLOAD workqueue jobs will run, and everything will wait for
clp->cl_cb_inflight to go to 0. That won't happen until the CB_OFFLOAD
jobs complete.

No objection from me though if you see a better approach. Dropping this
one for now seems reasonable.

> 
> > Maybe this CB_OFFLOAD shouldn't retry on DELAY?
> > 
> > 
> > >  }
> > >  #ifdef CONFIG_NFSD_V4_2_INTER_SSC
> > >  
> > 
> > 
> > -- 
> > Jeff Layton <jlayton@kernel.org>
> > 
> 

-- 
Jeff Layton <jlayton@kernel.org>