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 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 smtp.lore.kernel.org (Postfix) with ESMTPS id 0D034C433F5 for ; Tue, 14 Dec 2021 15:07:45 +0000 (UTC) Received: from localhost ([::1]:58970 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1mx9P5-00022a-Sz for qemu-devel@archiver.kernel.org; Tue, 14 Dec 2021 10:07:44 -0500 Received: from eggs.gnu.org ([209.51.188.92]:47342) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1mx9Ha-0007OA-VI for qemu-devel@nongnu.org; Tue, 14 Dec 2021 09:59:59 -0500 Received: from us-smtp-delivery-124.mimecast.com ([170.10.129.124]:30702) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1mx9HZ-00015k-0N for qemu-devel@nongnu.org; Tue, 14 Dec 2021 09:59:58 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1639493995; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=rOoT+y37XhAMWSTS76ol8Ujc8USecQx3HLnDfWnxJRs=; b=GvPIixrO3IzuXLZ2oHmBtVXKZnZL6SEbc8y46xayhxnxuWqsBQ39mSM0djI4peQDSiE2MZ Kqfb5A3ZvMOOa/wLYa5almYUxcM1NqJIEyeWHyifpFe26GBSJhb/6TqGmOIv7YSOWP53Nx ocHtCijBhH4B3uuIS4pzFtD4FgWBQTs= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-575-QbGaoid_PYGD6RET05h-xg-1; Tue, 14 Dec 2021 09:59:54 -0500 X-MC-Unique: QbGaoid_PYGD6RET05h-xg-1 Received: from smtp.corp.redhat.com (int-mx04.intmail.prod.int.phx2.redhat.com [10.5.11.14]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 1FADF2F47; Tue, 14 Dec 2021 14:59:53 +0000 (UTC) Received: from redhat.com (unknown [10.39.195.29]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 96B5C5ED4F; Tue, 14 Dec 2021 14:59:51 +0000 (UTC) Date: Tue, 14 Dec 2021 15:59:49 +0100 From: Kevin Wolf To: Stefan Hajnoczi Subject: Re: [PATCH v2] block-backend: prevent dangling BDS pointers across aio_poll() Message-ID: References: <20211214143542.14758-1-stefanha@redhat.com> MIME-Version: 1.0 In-Reply-To: <20211214143542.14758-1-stefanha@redhat.com> X-Scanned-By: MIMEDefang 2.79 on 10.5.11.14 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=kwolf@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Received-SPF: pass client-ip=170.10.129.124; envelope-from=kwolf@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -34 X-Spam_score: -3.5 X-Spam_bar: --- X-Spam_report: (-3.5 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.716, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_LOW=-0.7, RCVD_IN_MSPIKE_H3=0.001, RCVD_IN_MSPIKE_WL=0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Hanna Reitz , Vladimir Sementsov-Ogievskiy , qemu-devel@nongnu.org, qemu-block@nongnu.org, qemu-stable@nongnu.org Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" Am 14.12.2021 um 15:35 hat Stefan Hajnoczi geschrieben: > The BlockBackend root child can change when aio_poll() is invoked. This > happens when a temporary filter node is removed upon blockjob > completion, for example. > > Functions in block/block-backend.c must be aware of this when using a > blk_bs() pointer across aio_poll() because the BlockDriverState refcnt > may reach 0, resulting in a stale pointer. > > One example is scsi_device_purge_requests(), which calls blk_drain() to > wait for in-flight requests to cancel. If the backup blockjob is active, > then the BlockBackend root child is a temporary filter BDS owned by the > blockjob. The blockjob can complete during bdrv_drained_begin() and the > last reference to the BDS is released when the temporary filter node is > removed. This results in a use-after-free when blk_drain() calls > bdrv_drained_end(bs) on the dangling pointer. > > Explicitly hold a reference to bs across block APIs that invoke > aio_poll(). > > Signed-off-by: Stefan Hajnoczi > --- > v2: > - Audit block/block-backend.c and fix additional cases > --- > block/block-backend.c | 11 +++++++++++ > 1 file changed, 11 insertions(+) > > diff --git a/block/block-backend.c b/block/block-backend.c > index 12ef80ea17..a40ad7fa92 100644 > --- a/block/block-backend.c > +++ b/block/block-backend.c > @@ -828,10 +828,12 @@ void blk_remove_bs(BlockBackend *blk) > notifier_list_notify(&blk->remove_bs_notifiers, blk); > if (tgm->throttle_state) { > bs = blk_bs(blk); > + bdrv_ref(bs); > bdrv_drained_begin(bs); > throttle_group_detach_aio_context(tgm); > throttle_group_attach_aio_context(tgm, qemu_get_aio_context()); > bdrv_drained_end(bs); > + bdrv_unref(bs); > } > > blk_update_root_state(blk); This hunk is unnecessary, we still hold a reference that is only given up a few lines down with bdrv_root_unref_child(root). The rest looks good to me, so without this hunk: Reviewed-by: Kevin Wolf