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=-8.6 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY, SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 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 780B6C432C1 for ; Tue, 24 Sep 2019 01:06:41 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 4372F20820 for ; Tue, 24 Sep 2019 01:06:41 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1569287201; bh=MZsQhhuRGcS97XGINQPk3TBqee6+7XKPTNL9WWEWBhY=; h=Date:From:To:Cc:Subject:List-ID:From; b=1vM6RyQO9R3lUwJRLigpllDFwNf+skQ8FgrYFEUkscOhVrjRbewqeToYgTjrV6Lcu wKPqGGiJcStNvClvVSUABmqWKsXmv+iTyoyMzSrmP0S0a/cKla9ndvd7mhhOVwHm4A M5asS9i+UnIe86E5Id9SC7b/ExJOv8x+CF/cQknU= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2503800AbfIXBGk (ORCPT ); Mon, 23 Sep 2019 21:06:40 -0400 Received: from mail-qt1-f193.google.com ([209.85.160.193]:42741 "EHLO mail-qt1-f193.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2392131AbfIXBGk (ORCPT ); Mon, 23 Sep 2019 21:06:40 -0400 Received: by mail-qt1-f193.google.com with SMTP id w14so173064qto.9 for ; Mon, 23 Sep 2019 18:06:38 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=sender:date:from:to:cc:subject:message-id:mime-version :content-disposition:user-agent; bh=6DGshTg/RMbL5O9kzlRUE9xMe5D6/chfzSidGhJCLUY=; b=fRNFBI3znk2eSlVtM+9P2CHvI2nbGZHR8wzd9rhIHEXgfbR2xXmQjrKKToBAGW0FwT 1Y/T2mqCmgLj8kgB4NwnMKdw8z2VRBl1ZZDQHNChNLxOaCewl8/g3eJHWGIBzpG0uzm4 Kj4f3ag8sccnEGEyK2TLreT+GXZB4TN3Vp4dyr4pd1RrTeOXsMho2Yk2KFHgFqDgUglv VZYMdcY2lnxmT9eCThj7f3oSwVdXhAMyQQM84rGKN8d0RUR+hSWy4KO3IGkPvMKiZ0Os OX7wMuOy8wPBCCAlLWtz4+uWLUGGSVOAgTFepHAzqqhuTp6a+uv/zYvuPHlhKZtHvhX9 cE5w== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:sender:date:from:to:cc:subject:message-id :mime-version:content-disposition:user-agent; bh=6DGshTg/RMbL5O9kzlRUE9xMe5D6/chfzSidGhJCLUY=; b=KmINo/pFsXzMoOOaJuY+vWxndhaVoC2QlBu+pbgKJ8K5qA0HKvPQfolSAFc/3uEqwW LBjD6BwLw44zxP7Pqwz+LuUziAQRMp7lwfZKMOeXfeNVBJVQJvtDboOOHadjqi7OFpUh 37k6I2jwjxWoqkm82CElu7uqRaASPIt9mKmZFrXlfeP/M5cCXyReP4q670aUeWA7iF7q XhoY7PcFM5WA67V8RSRWYyMM8KBCp5WCkm9MoqBPYFsE8muwp4V1cMttj8Cc1C99lKIG SKxfeufN3q2O7EgIX6XKKRz42Yj8PPme2c0gY1oNk9i0yTdSiPE70NKAo+bgifa8esvl EvSA== X-Gm-Message-State: APjAAAUw09cvI1y9ttJeoiRJpLgyQOOeiMTjRMXu3vtfQ3l2CzqztOxB rZVQrdIeYKeOFKZuSmC4i5dh43/vnjU= X-Google-Smtp-Source: APXvYqwyJjQcYBAybizwpkS6SzD/rQ/6BPTGNIaL6BVjH7KAYcufcKuiAXv5I2PlqkaxLRUkptru3Q== X-Received: by 2002:ac8:4597:: with SMTP id l23mr332247qtn.284.1569287198141; Mon, 23 Sep 2019 18:06:38 -0700 (PDT) Received: from localhost ([2620:10d:c091:480::737b]) by smtp.gmail.com with ESMTPSA id d23sm49884qkc.127.2019.09.23.18.06.37 (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Mon, 23 Sep 2019 18:06:37 -0700 (PDT) Date: Mon, 23 Sep 2019 18:06:31 -0700 From: Tejun Heo To: Andrew Morton Cc: Jan Kara , linux-kernel@vger.kernel.org, kernel-team@fb.com, Jens Axboe Subject: [PATCH] writeback: fix use-after-free in finish_writeback_work() Message-ID: <20190924010631.GH2233839@devbig004.ftw2.facebook.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org finish_writeback_work() reads @done->waitq after decrementing @done->cnt. However, once @done->cnt reaches zero, @done may be freed (from stack) at any moment and @done->waitq can contain something unrelated by the time finish_writeback_work() tries to read it. This led to the following crash. "BUG: kernel NULL pointer dereference, address: 0000000000000002" #PF: supervisor write access in kernel mode #PF: error_code(0x0002) - not-present page PGD 0 P4D 0 Oops: 0002 [#1] SMP DEBUG_PAGEALLOC CPU: 40 PID: 555153 Comm: kworker/u98:50 Kdump: loaded Not tainted ... Workqueue: writeback wb_workfn (flush-btrfs-1) RIP: 0010:_raw_spin_lock_irqsave+0x10/0x30 Code: 48 89 d8 5b c3 e8 50 db 6b ff eb f4 0f 1f 40 00 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 44 00 00 53 9c 5b fa 31 c0 ba 01 00 00 00 0f b1 17 75 05 48 89 d8 5b c3 89 c6 e8 fe ca 6b ff eb f2 66 90 RSP: 0018:ffffc90049b27d98 EFLAGS: 00010046 RAX: 0000000000000000 RBX: 0000000000000246 RCX: 0000000000000000 RDX: 0000000000000001 RSI: 0000000000000003 RDI: 0000000000000002 RBP: 0000000000000000 R08: 0000000000000000 R09: 0000000000000001 R10: ffff889fff407600 R11: ffff88ba9395d740 R12: 000000000000e300 R13: 0000000000000003 R14: 0000000000000000 R15: 0000000000000000 FS: 0000000000000000(0000) GS:ffff88bfdfa00000(0000) knlGS:0000000000000000 CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 CR2: 0000000000000002 CR3: 0000000002409005 CR4: 00000000001606e0 Call Trace: __wake_up_common_lock+0x63/0xc0 wb_workfn+0xd2/0x3e0 process_one_work+0x1f5/0x3f0 worker_thread+0x2d/0x3d0 kthread+0x111/0x130 ret_from_fork+0x1f/0x30 Fix it by reading and caching @done->waitq before decrementing @done->cnt. Signed-off-by: Tejun Heo Debugged-by: Chris Mason Fixes: 30638b0125e1 ("writeback: Generalize and expose wb_completion") Cc: stable@vger.kernel.org # v5.2+ --- fs/fs-writeback.c | 9 +++++++-- 1 file changed, 7 insertions(+), 2 deletions(-) diff --git a/fs/fs-writeback.c b/fs/fs-writeback.c index 8aaa7eec7b74..e88421d9a48d 100644 --- a/fs/fs-writeback.c +++ b/fs/fs-writeback.c @@ -164,8 +164,13 @@ static void finish_writeback_work(struct bdi_writeback *wb, if (work->auto_free) kfree(work); - if (done && atomic_dec_and_test(&done->cnt)) - wake_up_all(done->waitq); + if (done) { + wait_queue_head_t *waitq = done->waitq; + + /* @done can't be accessed after the following dec */ + if (atomic_dec_and_test(&done->cnt)) + wake_up_all(waitq); + } } static void wb_queue_work(struct bdi_writeback *wb,