Re: [PATCH] nfs: fix NULL deference in nfs4_get_valid_delegation

["bfields@fieldses.org" <bfields@fieldses.org>]

On Mon, May 11, 2020 at 01:37:23PM -0400, Masayoshi Mizuma wrote:
> Hello,
> 
> How about adding Cc: stable@vger.kernel.org in the sign-off area?
> 9ae075fdd190 "NFSv4: Convert open state lookup to use RCU" was merged

Makes sense to me.  I'll leave it to Trond.--b.

> to v4.20 and some stable tree have 9ae075fdd190.
> 
> On Mon, May 11, 2020 at 10:02:48AM -0400, bfields@fieldses.org wrote:
> > From: "J. Bruce Fields" <bfields@redhat.com>
> > 
> > We add the new state to the nfsi->open_states list, making it
> > potentially visible to other threads, before we've finished initializing
> > it.
> > 
> > That wasn't a problem when all the readers were also taking the i_lock
> > (as we do here), but since we switched to RCU, there's now a possibility
> > that a reader could see the partially initialized state.
> > 
> > Symptoms observed were a crash when another thread called
> > nfs4_get_valid_delegation() on a NULL inode, resulting in an oops like:
> > 
> > 	BUG: unable to handle page fault for address: ffffffffffffffb0 ...
> > 	RIP: 0010:nfs4_get_valid_delegation+0x6/0x30 [nfsv4] ...
> > 	Call Trace:
> > 	 nfs4_open_prepare+0x80/0x1c0 [nfsv4]
> > 	 __rpc_execute+0x75/0x390 [sunrpc]
> > 	 ? finish_task_switch+0x75/0x260
> > 	 rpc_async_schedule+0x29/0x40 [sunrpc]
> > 	 process_one_work+0x1ad/0x370
> > 	 worker_thread+0x30/0x390
> > 	 ? create_worker+0x1a0/0x1a0
> > 	 kthread+0x10c/0x130
> > 	 ? kthread_park+0x80/0x80
> > 	 ret_from_fork+0x22/0x30
> > 
> > Fixes: 9ae075fdd190 "NFSv4: Convert open state lookup to use RCU"
> 
> Cc: stable@vger.kernel.org # 4.20.x-
> 
> Thanks!
> Masa
> 
> > Reviewed-by: Seiichi Ikarashi <s.ikarashi@fujitsu.com>
> > Tested-by: Daisuke Matsuda <matsuda-daisuke@fujitsu.com>
> > Tested-by: Masayoshi Mizuma <m.mizuma@jp.fujitsu.com>
> > Signed-off-by: J. Bruce Fields <bfields@redhat.com>
> > ---
> >  fs/nfs/nfs4state.c | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> > 
> > > I do have a patch including the tags and oops provided by Masayoshi
> > > Mizuma, if you'd like to take that instead.  See followup.--b.
> > 
> > Here you go.
> > 
> > diff --git a/fs/nfs/nfs4state.c b/fs/nfs/nfs4state.c
> > index f7723d221945..459c7fb5d103 100644
> > --- a/fs/nfs/nfs4state.c
> > +++ b/fs/nfs/nfs4state.c
> > @@ -734,9 +734,9 @@ nfs4_get_open_state(struct inode *inode, struct nfs4_state_owner *owner)
> >  		state = new;
> >  		state->owner = owner;
> >  		atomic_inc(&owner->so_count);
> > -		list_add_rcu(&state->inode_states, &nfsi->open_states);
> >  		ihold(inode);
> >  		state->inode = inode;
> > +		list_add_rcu(&state->inode_states, &nfsi->open_states);
> >  		spin_unlock(&inode->i_lock);
> >  		/* Note: The reclaim code dictates that we add stateless
> >  		 * and read-only stateids to the end of the list */
> > -- 
> > 2.26.2
> >