From nobody Mon Feb 23 01:03:38 2026 Delivered-To: importer@patchew.org Authentication-Results: mx.zohomail.com; dkim=fail; spf=pass (zohomail.com: domain of gnu.org designates 209.51.188.17 as permitted sender) smtp.mailfrom=qemu-devel-bounces+importer=patchew.org@nongnu.org; dmarc=fail(p=none dis=none) header.from=redhat.com Return-Path: Received: from lists.gnu.org (lists.gnu.org [209.51.188.17]) by mx.zohomail.com with SMTPS id 1641915512633435.10447231619946; Tue, 11 Jan 2022 07:38:32 -0800 (PST) Received: from localhost ([::1]:57084 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1n7JEF-0003bc-HK for importer@patchew.org; Tue, 11 Jan 2022 10:38:31 -0500 Received: from eggs.gnu.org ([209.51.188.92]:37600) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1n7JCL-0000cV-BC for qemu-devel@nongnu.org; Tue, 11 Jan 2022 10:36:33 -0500 Received: from us-smtp-delivery-124.mimecast.com ([170.10.129.124]:33288) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1n7JCH-0000iB-IN for qemu-devel@nongnu.org; Tue, 11 Jan 2022 10:36:33 -0500 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-213-Q-HO1594OCyqc-UVT_Ut2g-1; Tue, 11 Jan 2022 10:36:24 -0500 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 mimecast-mx01.redhat.com (Postfix) with ESMTPS id A54EB1966322; Tue, 11 Jan 2022 15:36:23 +0000 (UTC) Received: from localhost (unknown [10.39.192.97]) by smtp.corp.redhat.com (Postfix) with ESMTP id 4C2F94EC84; Tue, 11 Jan 2022 15:36:20 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1641915387; 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: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=ZSWv9JVuS8m91TEuYQoQm6tm2E7qO0d9cvbUGRdmc5s=; b=ZX1xHTaaBv1WO+Cwj4vuHt/iForf76B5niODbpa9NIcDlVGxM2DTHvX4XQdEEdJNCngfoS ThO1cxgfBxjUpkFyrchqtHWHCPgr/cZ07OJBwEQBaiEBDUUoRicGt5CD364Xhe2gK1Bdtz KRv1VUiL0SzslhfyibVaC4qe/4sSHH8= X-MC-Unique: Q-HO1594OCyqc-UVT_Ut2g-1 From: Stefan Hajnoczi To: qemu-devel@nongnu.org Subject: [PATCH v3 1/2] block-backend: prevent dangling BDS pointers across aio_poll() Date: Tue, 11 Jan 2022 15:36:12 +0000 Message-Id: <20220111153613.25453-2-stefanha@redhat.com> In-Reply-To: <20220111153613.25453-1-stefanha@redhat.com> References: <20220111153613.25453-1-stefanha@redhat.com> MIME-Version: 1.0 X-Scanned-By: MIMEDefang 2.79 on 10.5.11.15 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=stefanha@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Transfer-Encoding: quoted-printable Received-SPF: pass (zohomail.com: domain of gnu.org designates 209.51.188.17 as permitted sender) client-ip=209.51.188.17; envelope-from=qemu-devel-bounces+importer=patchew.org@nongnu.org; helo=lists.gnu.org; Received-SPF: pass client-ip=170.10.129.124; envelope-from=stefanha@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -33 X-Spam_score: -3.4 X-Spam_bar: --- X-Spam_report: (-3.4 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.595, 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=unavailable 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: Kevin Wolf , Vladimir Sementsov-Ogievskiy , qemu-block@nongnu.org, qemu-stable@nongnu.org, Hanna Reitz , Stefan Hajnoczi Errors-To: qemu-devel-bounces+importer=patchew.org@nongnu.org Sender: "Qemu-devel" X-ZohoMail-DKIM: fail (Header signature does not verify) X-ZM-MESSAGEID: 1641915514302100001 Content-Type: text/plain; charset="utf-8" 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(). Buglink: https://bugzilla.redhat.com/show_bug.cgi?id=3D2021778 Buglink: https://bugzilla.redhat.com/show_bug.cgi?id=3D2036178 Signed-off-by: Stefan Hajnoczi --- v3: - Add comment in blk_remove_bs() and reduce scope of bs local variable [Kev= in] v2: - Audit block/block-backend.c and fix additional cases --- block/block-backend.c | 19 +++++++++++++++++-- 1 file changed, 17 insertions(+), 2 deletions(-) diff --git a/block/block-backend.c b/block/block-backend.c index 12ef80ea17..23e727199b 100644 --- a/block/block-backend.c +++ b/block/block-backend.c @@ -822,16 +822,22 @@ BlockBackend *blk_by_public(BlockBackendPublic *publi= c) void blk_remove_bs(BlockBackend *blk) { ThrottleGroupMember *tgm =3D &blk->public.throttle_group_member; - BlockDriverState *bs; BdrvChild *root; =20 notifier_list_notify(&blk->remove_bs_notifiers, blk); if (tgm->throttle_state) { - bs =3D blk_bs(blk); + BlockDriverState *bs =3D blk_bs(blk); + + /* + * Take a ref in case blk_bs() changes across bdrv_drained_begin()= , for + * example, if a temporary filter node is removed by a blockjob. + */ + 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); } =20 blk_update_root_state(blk); @@ -1705,6 +1711,7 @@ void blk_drain(BlockBackend *blk) BlockDriverState *bs =3D blk_bs(blk); =20 if (bs) { + bdrv_ref(bs); bdrv_drained_begin(bs); } =20 @@ -1714,6 +1721,7 @@ void blk_drain(BlockBackend *blk) =20 if (bs) { bdrv_drained_end(bs); + bdrv_unref(bs); } } =20 @@ -2044,10 +2052,13 @@ static int blk_do_set_aio_context(BlockBackend *blk= , AioContext *new_context, int ret; =20 if (bs) { + bdrv_ref(bs); + if (update_root_node) { ret =3D bdrv_child_try_set_aio_context(bs, new_context, blk->r= oot, errp); if (ret < 0) { + bdrv_unref(bs); return ret; } } @@ -2057,6 +2068,8 @@ static int blk_do_set_aio_context(BlockBackend *blk, = AioContext *new_context, throttle_group_attach_aio_context(tgm, new_context); bdrv_drained_end(bs); } + + bdrv_unref(bs); } =20 blk->ctx =3D new_context; @@ -2326,11 +2339,13 @@ void blk_io_limits_disable(BlockBackend *blk) ThrottleGroupMember *tgm =3D &blk->public.throttle_group_member; assert(tgm->throttle_state); if (bs) { + bdrv_ref(bs); bdrv_drained_begin(bs); } throttle_group_unregister_tgm(tgm); if (bs) { bdrv_drained_end(bs); + bdrv_unref(bs); } } =20 --=20 2.33.1