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 A0627C433FE for ; Tue, 14 Dec 2021 14:37:23 +0000 (UTC) Received: from localhost ([::1]:37022 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1mx8vi-0000cU-8f for qemu-devel@archiver.kernel.org; Tue, 14 Dec 2021 09:37:22 -0500 Received: from eggs.gnu.org ([209.51.188.92]:42154) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1mx8uf-0007aL-HY for qemu-devel@nongnu.org; Tue, 14 Dec 2021 09:36:17 -0500 Received: from us-smtp-delivery-124.mimecast.com ([170.10.129.124]:27092) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1mx8uc-0006Mj-E8 for qemu-devel@nongnu.org; Tue, 14 Dec 2021 09:36:16 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1639492573; 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; bh=zMEHm8d02ZPN/1SRCzxKaBTl4WXAIqs7NnA+bfaq7IA=; b=KOu7ENeXvvlMwtRl3ff8t8aldGnuOCQUp8eQPOWH7n4chSJNd9eATp5KP7d0zoeW+acdJv rqxCHGzn5kcPwBEBcb50H+gPWAqBYoD4KbHN7izgZ170F1NuKO7ijstC8UY2ru1weOjKqW xjpXbJNUpHHPFdiJyxspKB9tTT0waHU= 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-459-fsRpgwQfNNufpWcFv9wS0Q-1; Tue, 14 Dec 2021 09:36:12 -0500 X-MC-Unique: fsRpgwQfNNufpWcFv9wS0Q-1 Received: from smtp.corp.redhat.com (int-mx08.intmail.prod.int.phx2.redhat.com [10.5.11.23]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 5AB1010168C7; Tue, 14 Dec 2021 14:36:11 +0000 (UTC) Received: from localhost (unknown [10.39.195.51]) by smtp.corp.redhat.com (Postfix) with ESMTP id EB37B1F423; Tue, 14 Dec 2021 14:35:43 +0000 (UTC) From: Stefan Hajnoczi To: qemu-devel@nongnu.org Subject: [PATCH v2] block-backend: prevent dangling BDS pointers across aio_poll() Date: Tue, 14 Dec 2021 14:35:42 +0000 Message-Id: <20211214143542.14758-1-stefanha@redhat.com> MIME-Version: 1.0 X-Scanned-By: MIMEDefang 2.84 on 10.5.11.23 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: 8bit Content-Type: text/plain; charset="US-ASCII" 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: -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: Kevin Wolf , Vladimir Sementsov-Ogievskiy , qemu-block@nongnu.org, qemu-stable@nongnu.org, Hanna Reitz , Stefan Hajnoczi Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" 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); @@ -1705,6 +1707,7 @@ void blk_drain(BlockBackend *blk) BlockDriverState *bs = blk_bs(blk); if (bs) { + bdrv_ref(bs); bdrv_drained_begin(bs); } @@ -1714,6 +1717,7 @@ void blk_drain(BlockBackend *blk) if (bs) { bdrv_drained_end(bs); + bdrv_unref(bs); } } @@ -2044,10 +2048,13 @@ static int blk_do_set_aio_context(BlockBackend *blk, AioContext *new_context, int ret; if (bs) { + bdrv_ref(bs); + if (update_root_node) { ret = bdrv_child_try_set_aio_context(bs, new_context, blk->root, errp); if (ret < 0) { + bdrv_unref(bs); return ret; } } @@ -2057,6 +2064,8 @@ 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); } blk->ctx = new_context; @@ -2326,11 +2335,13 @@ void blk_io_limits_disable(BlockBackend *blk) ThrottleGroupMember *tgm = &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); } } -- 2.33.1