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=-6.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS 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 064C1C3A5A1 for ; Thu, 22 Aug 2019 15:55:03 +0000 (UTC) Received: from lists.gnu.org (lists.gnu.org [209.51.188.17]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id CC6682089E for ; Thu, 22 Aug 2019 15:55:02 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org CC6682089E Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=redhat.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Received: from localhost ([::1]:44748 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1i0pQT-0004RG-Ub for qemu-devel@archiver.kernel.org; Thu, 22 Aug 2019 11:55:02 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:57800) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1i0pOx-0002nU-Nr for qemu-devel@nongnu.org; Thu, 22 Aug 2019 11:53:28 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1i0pOw-0003nJ-Kh for qemu-devel@nongnu.org; Thu, 22 Aug 2019 11:53:27 -0400 Received: from mx1.redhat.com ([209.132.183.28]:54908) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1i0pOu-0003kd-AW; Thu, 22 Aug 2019 11:53:24 -0400 Received: from smtp.corp.redhat.com (int-mx05.intmail.prod.int.phx2.redhat.com [10.5.11.15]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 9BB332BFDC; Thu, 22 Aug 2019 15:53:23 +0000 (UTC) Received: from localhost (ovpn-116-61.ams2.redhat.com [10.36.116.61]) by smtp.corp.redhat.com (Postfix) with ESMTP id 3D66E5D772; Thu, 22 Aug 2019 15:53:15 +0000 (UTC) From: Stefan Hajnoczi To: qemu-devel@nongnu.org Date: Thu, 22 Aug 2019 16:53:01 +0100 Message-Id: <20190822155302.20916-2-stefanha@redhat.com> In-Reply-To: <20190822155302.20916-1-stefanha@redhat.com> References: <20190822155302.20916-1-stefanha@redhat.com> MIME-Version: 1.0 X-Scanned-By: MIMEDefang 2.79 on 10.5.11.15 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.39]); Thu, 22 Aug 2019 15:53:23 +0000 (UTC) Content-Transfer-Encoding: quoted-printable X-detected-operating-system: by eggs.gnu.org: GNU/Linux 2.2.x-3.x [generic] X-Received-From: 209.132.183.28 Subject: [Qemu-devel] [PULL 1/2] util/async: hold AioContext ref to prevent use-after-free X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Fam Zheng , Peter Maydell , qemu-block@nongnu.org, "Michael S. Tsirkin" , Stefan Hajnoczi , Paolo Bonzini Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" The tests/test-bdrv-drain /bdrv-drain/iothread/drain test case does the following: 1. The preadv coroutine calls aio_bh_schedule_oneshot() and then yields. 2. The one-shot BH executes in another AioContext. All it does is call aio_co_wakeup(preadv_co). 3. The preadv coroutine is re-entered and returns. There is a race condition in aio_co_wake() where the preadv coroutine returns and the test case destroys the preadv IOThread. aio_co_wake() can still be running in the other AioContext and it performs an access to the freed IOThread AioContext. Here is the race in aio_co_schedule(): QSLIST_INSERT_HEAD_ATOMIC(&ctx->scheduled_coroutines, co, co_scheduled_next); <-- race: co may execute before we invoke qemu_bh_schedule()! qemu_bh_schedule(ctx->co_schedule_bh); So if co causes ctx to be freed then we're in trouble. Fix this problem by holding a reference to ctx. Signed-off-by: Stefan Hajnoczi Reviewed-by: Paolo Bonzini Message-id: 20190723190623.21537-1-stefanha@redhat.com Message-Id: <20190723190623.21537-1-stefanha@redhat.com> Signed-off-by: Stefan Hajnoczi --- util/async.c | 8 ++++++++ 1 file changed, 8 insertions(+) diff --git a/util/async.c b/util/async.c index 8d2105729c..4e4c7af51e 100644 --- a/util/async.c +++ b/util/async.c @@ -459,9 +459,17 @@ void aio_co_schedule(AioContext *ctx, Coroutine *co) abort(); } =20 + /* The coroutine might run and release the last ctx reference before= we + * invoke qemu_bh_schedule(). Take a reference to keep ctx alive un= til + * we're done. + */ + aio_context_ref(ctx); + QSLIST_INSERT_HEAD_ATOMIC(&ctx->scheduled_coroutines, co, co_scheduled_next); qemu_bh_schedule(ctx->co_schedule_bh); + + aio_context_unref(ctx); } =20 void aio_co_wake(struct Coroutine *co) --=20 2.21.0