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=-0.6 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,FREEMAIL_FORGED_FROMDOMAIN,FREEMAIL_FROM, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS autolearn=no 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 4D617C432C0 for ; Thu, 28 Nov 2019 03:03:57 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 1075F215A4 for ; Thu, 28 Nov 2019 03:03:57 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b="IeO5i5e7" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727563AbfK1DD4 (ORCPT ); Wed, 27 Nov 2019 22:03:56 -0500 Received: from mail-ed1-f68.google.com ([209.85.208.68]:43731 "EHLO mail-ed1-f68.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727191AbfK1DD4 (ORCPT ); Wed, 27 Nov 2019 22:03:56 -0500 Received: by mail-ed1-f68.google.com with SMTP id dc19so6499197edb.10 for ; Wed, 27 Nov 2019 19:03:55 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=mime-version:from:date:message-id:subject:to; bh=MA5gajHF1GyLnbdtQ1P4c4Q7951U6L+/3dn2e5BFp1o=; b=IeO5i5e7szJPcYtgGW7+1A6P+WnOIo2f6gw826oqAoX7Ar4OPcKCVnHrrBvB05Qsc0 +F0cA+LkUay4AWilXnYPm0P0oyImOooFylFODrZltkMrwvjeyP0IKjujjUXMdQKCjwpz sQ6e2X5JxqJXc+fPyIRy7sZiP6knTrV0uB/qxBsXoU9W/7Qi2vUWFaTZ6A6I7ptS2/Jz Vh28ENfUnXZHA7LIC+ytQ0pRg57a6SdxcpUg5Ux2X3K4XpHqGKevBqZKZ2/zuQK5zp/q 8kcYQIw26x2YuF6QUyTh9wQqxYTRkkNrewCO7TKTnIgJBgkiXjNjbausGSB81J8KMbnK 4K4g== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:from:date:message-id:subject:to; bh=MA5gajHF1GyLnbdtQ1P4c4Q7951U6L+/3dn2e5BFp1o=; b=DFiqRQcvOIh8WrYDfh/pspalwDGrsU2/PEW0RPfHFK85vvNkoH20VuICfeCYyXYF78 FoV0zDNDP3MkfQwDXJQFw4KEE/PMZqGaISuj8jNxTjJjEEdc46IBvFkUnwliUavPBfmZ /ajltLB+AY5Ng1/vIsE+lRty+ouZ4bTan9o1df5iXBJqK44bJRFtD2Pp+CpoSeyNfAAd KVwfUbiWDz1Fezs+lwqIK54dbRtdz96bNAz3REcHOLkk0CEKVKugndckkMWa3QF9Jl7k 4aHdLHFW0fnZ0BBwwWsGOzG9idjXVU4G7kdZjUpDOp8AQ83f01QctsPgEeH5EF10wJXM lkKA== X-Gm-Message-State: APjAAAWUMC5BhzGCzo5s5opZkxNw5+UUrXbNbvAKD2lbTXIICsM+DCNq uacazOBGlL4lEsV9JRlMrjB84+YUHZcaUVNnmNX/3EC0 X-Google-Smtp-Source: APXvYqzfpDiQZgV4pDx9NCT3hORrUZEbWzdqwR/wHhumgEG5Ye1nHKgV2ikSieevnAO6EgaFos9yE4QfFO20z9zodLg= X-Received: by 2002:a05:6402:b2d:: with SMTP id bo13mr34654055edb.125.1574909817590; Wed, 27 Nov 2019 18:56:57 -0800 (PST) MIME-Version: 1.0 From: Meng Xu Date: Wed, 27 Nov 2019 21:56:46 -0500 Message-ID: Subject: Potential data race on the file->f_pos field between getdents and sendfile To: linux-fsdevel@vger.kernel.org Content-Type: text/plain; charset="UTF-8" Sender: linux-fsdevel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@vger.kernel.org Hi VFS developers, I am posting here a potential data race on the file->f_pos field between getdents and sendfile. Following is the trace: [Setup] mkdir("foo", 511) = 0; open("foo", 65536, 511) = 3; dup2(3, 199) = 199; create("bar", 511) = 4; dup2(4, 198) = 198; [Thread 1] getdents(199, [some buffer], 3874); __do_sys_getdents iterate_dir [WRITE] file->f_pos = ctx->pos; [Thread 2] sendfile(198, 199, NULL, 2163); __do_sys_sendfile64 do_sendfile [READ] pos = in.file->f_pos; This may be a false data race, i.e., the behavior could be allowed by POSIX as user might want to sendfile to a dirfd while the dirfd is being iterated (although there is no obvious reason for doing so). I am posting this here for more visibility and feel free to comment. Best Regards, Meng