From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-3.0 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS,USER_AGENT_GIT autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 6ADDCC04AAA for ; Mon, 13 May 2019 15:27:07 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 48A622084A for ; Mon, 13 May 2019 15:27:07 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727458AbfEMP1G (ORCPT ); Mon, 13 May 2019 11:27:06 -0400 Received: from fieldses.org ([173.255.197.46]:58464 "EHLO fieldses.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727437AbfEMP1G (ORCPT ); Mon, 13 May 2019 11:27:06 -0400 Received: by fieldses.org (Postfix, from userid 2815) id 6C19C1D39; Mon, 13 May 2019 11:27:05 -0400 (EDT) From: "J. Bruce Fields" To: linux-nfs@vger.kernel.org Cc: "J. Bruce Fields" Subject: [PATCH 0/2] nfsd shoudn't call mnt_want_write twice Date: Mon, 13 May 2019 11:27:01 -0400 Message-Id: <1557761223-14483-1-git-send-email-bfields@redhat.com> X-Mailer: git-send-email 1.8.3.1 Sender: linux-nfs-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-nfs@vger.kernel.org From: "J. Bruce Fields" A fuzzer recently triggered lockdep warnings about potential sb_writers deadlocks caused by fh_want_write, showing that we haven't been careful to pair each fh_want_write() with an fh_drop_write(). This isn't normally a problem since fh_put() will call fh_drop_write() for us. And that's OK for NFSv3. But an NFSv4 protocol fuzzer can do weird things like call unlink twice in a compound. So we can either make it safe to call fh_want_write() twice, or we can fix all the callers to call fh_drop_write(). For now I think we have to do the former just to get the bug fixed. Long term I don't know whether it's best to stay with that or to fix up the callers. I fixed nfsd_unlink just because it's easy, but maybe that's pointless, it's others (like setattr) that are the complicated ones. J. Bruce Fields (2): nfsd: allow fh_want_write to be called twice nfsd: fh_drop_write in nfsd_unlink fs/nfsd/vfs.c | 8 +++++--- fs/nfsd/vfs.h | 5 ++++- 2 files changed, 9 insertions(+), 4 deletions(-) -- 2.21.0