From patchwork Mon May 11 14:02:48 2020 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: "J. Bruce Fields" X-Patchwork-Id: 11540927 Return-Path: Received: from mail.kernel.org (pdx-korg-mail-1.web.codeaurora.org [172.30.200.123]) by pdx-korg-patchwork-2.web.codeaurora.org (Postfix) with ESMTP id 44E9192A for ; Mon, 11 May 2020 14:02:49 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 2D034206D3 for ; Mon, 11 May 2020 14:02:49 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727792AbgEKOCs (ORCPT ); Mon, 11 May 2020 10:02:48 -0400 Received: from fieldses.org ([173.255.197.46]:54488 "EHLO fieldses.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1729279AbgEKOCs (ORCPT ); Mon, 11 May 2020 10:02:48 -0400 Received: by fieldses.org (Postfix, from userid 2815) id 3E53528E6; Mon, 11 May 2020 10:02:48 -0400 (EDT) Date: Mon, 11 May 2020 10:02:48 -0400 From: "bfields@fieldses.org" To: Trond Myklebust Cc: "msys.mizuma@gmail.com" , "schumakeranna@gmail.com" , "linux-nfs@vger.kernel.org" Subject: [PATCH] nfs: fix NULL deference in nfs4_get_valid_delegation Message-ID: <20200511140248.GE8629@fieldses.org> References: <20200508221935.GA11225@fieldses.org> <20200511121054.l2j34vnwqxhvd2ao@gabell> <20200511131637.GA8629@fieldses.org> <8f9f84f11df6f5caf054d1eada2d91ea158a6882.camel@hammerspace.com> <20200511135745.GB8629@fieldses.org> <20200511140158.GD8629@fieldses.org> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <20200511140158.GD8629@fieldses.org> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-nfs-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-nfs@vger.kernel.org From: "J. Bruce Fields" 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" Reviewed-by: Seiichi Ikarashi Tested-by: Daisuke Matsuda Tested-by: Masayoshi Mizuma Signed-off-by: J. Bruce Fields --- 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 */