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=-5.4 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,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 356BFC54FD0 for ; Thu, 23 Apr 2020 18:19:34 +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 01C222071C for ; Thu, 23 Apr 2020 18:19:34 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="M5fHbaOP" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 01C222071C 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]:36212 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1jRgRh-0004Sj-65 for qemu-devel@archiver.kernel.org; Thu, 23 Apr 2020 14:19:33 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:57984) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1jRgQc-0002sc-Be for qemu-devel@nongnu.org; Thu, 23 Apr 2020 14:18:26 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.90_1) (envelope-from ) id 1jRgQa-00010h-SW for qemu-devel@nongnu.org; Thu, 23 Apr 2020 14:18:25 -0400 Received: from us-smtp-1.mimecast.com ([205.139.110.61]:28027 helo=us-smtp-delivery-1.mimecast.com) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_CBC_SHA1:256) (Exim 4.90_1) (envelope-from ) id 1jRgQa-0000xq-FA for qemu-devel@nongnu.org; Thu, 23 Apr 2020 14:18:24 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1587665903; 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=+xtdrzsF04zvBFlNFveofitFAjCVODi73AWwr6171FA=; b=M5fHbaOPC8T/IgW4zPUvYeJnb9DC/n01qc2ZwRYHtqvtKAyj60jqE93cVH3JHftieyrA2j x/157ZqvBuFJ+mdYLFdwm3w6gS6LZjhiEAWJrBRmuKWhq1nxfl+wxwQowoYGTcipknzfUy iz1UQJqb6YzVT1SynrYCmV7FsEwf5yY= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-122-rW-P051YOVuxgQjDd9RoNQ-1; Thu, 23 Apr 2020 14:18:19 -0400 X-MC-Unique: rW-P051YOVuxgQjDd9RoNQ-1 Received: from smtp.corp.redhat.com (int-mx03.intmail.prod.int.phx2.redhat.com [10.5.11.13]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 32D15800FC7; Thu, 23 Apr 2020 18:18:18 +0000 (UTC) Received: from [10.10.116.80] (ovpn-116-80.rdu2.redhat.com [10.10.116.80]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 948776084C; Thu, 23 Apr 2020 18:18:17 +0000 (UTC) Subject: Re: [PATCH 10/13] qapi: Clean up visitor's recovery from input with invalid type From: Eric Blake To: Markus Armbruster , qemu-devel@nongnu.org References: <20200423160036.7048-1-armbru@redhat.com> <20200423160036.7048-11-armbru@redhat.com> <435f2d5d-e732-a236-bf13-991d5c3510e6@redhat.com> Organization: Red Hat, Inc. Message-ID: <89636246-6a5c-476d-6016-977f39cb653c@redhat.com> Date: Thu, 23 Apr 2020 13:18:04 -0500 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.7.0 MIME-Version: 1.0 In-Reply-To: <435f2d5d-e732-a236-bf13-991d5c3510e6@redhat.com> Content-Language: en-US X-Scanned-By: MIMEDefang 2.79 on 10.5.11.13 X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: quoted-printable Received-SPF: pass client-ip=205.139.110.61; envelope-from=eblake@redhat.com; helo=us-smtp-delivery-1.mimecast.com X-detected-operating-system: by eggs.gnu.org: First seen = 2020/04/23 03:23:21 X-ACL-Warn: Detected OS = Linux 2.2.x-3.x [generic] X-Received-From: 205.139.110.61 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: mdroth@linux.vnet.ibm.com Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On 4/23/20 1:06 PM, Eric Blake wrote: > On 4/23/20 11:00 AM, Markus Armbruster wrote: >> An alternate type's visit_type_FOO() fails when it runs into an >> invalid ->type.=C2=A0 If it's an input visit, we then need to free the t= he >> object we got from visit_start_alternate().=C2=A0 We do that with >> qapi_free_FOO(), which uses the dealloc visitor. >> >> Trouble is that object is in a bad state: its ->type is invalid.=C2=A0 S= o >> the dealloc visitor will run into the same error again, and the error >> recovery skips deallocating the alternate's (invalid) alternative. >> This is a roundabout way to g_free() the alternate. >> >> Simplify: replace the qapi_free_FOO() by g_free(). >> >> Signed-off-by: Markus Armbruster >> --- >> =C2=A0 scripts/qapi/visit.py | 2 +- >> =C2=A0 1 file changed, 1 insertion(+), 1 deletion(-) >> >=20 > Required looking at what gets generated into qapi_free_FOO() as well as= =20 > when visit_start_alternate() can fail, but makes sense. >=20 > Reviewed-by: Eric Blake Actually, I'm having second thoughts. As an example, look at the generated= : > void visit_type_BlockDirtyBitmapMergeSource(Visitor *v, const char *name,= BlockDirtyBitmapMergeSource **obj, Error **errp) > { > Error *err =3D NULL; >=20 > visit_start_alternate(v, name, (GenericAlternate **)obj, sizeof(**obj= ), > &err); > if (err) { > goto out; > } > if (!*obj) { > goto out_obj; [1] > } > switch ((*obj)->type) { > case QTYPE_QSTRING: > visit_type_str(v, name, &(*obj)->u.local, &err); [2] > break; > case QTYPE_QDICT: > visit_start_struct(v, name, NULL, 0, &err); > if (err) { > break; [3] > } > visit_type_BlockDirtyBitmap_members(v, &(*obj)->u.external, &err)= ; > if (!err) { > visit_check_struct(v, &err); [4] > } > visit_end_struct(v, NULL); > break; > case QTYPE_NONE: > abort(); > default: > error_setg(&err, QERR_INVALID_PARAMETER_TYPE, name ? name : "null= ", > "BlockDirtyBitmapMergeSource"); [5] > } > out_obj: > visit_end_alternate(v, (void **)obj); > if (err && visit_is_input(v)) { > qapi_free_BlockDirtyBitmapMergeSource(*obj); If we got here, we must have failed at any of the points mentioned above. If [1], visit_start_alternate() failed, but *obj is NULL and both=20 qapi_free_FOO(NULL) and g_free(NULL) are safe. If [2], visit_type_str() failed, so *obj is allocated but the embedded=20 string (here, u.local) was left NULL. qapi_free_FOO() then does nothing=20 further than g_free(obj). If [3], visit_start_struct() failed, the embedded dict (here,=20 u.external) was left NULL. qapi_free_FOO() then does nothing further=20 than g_free(obj). If [5], we have the wrong ->type. As pointed out by this commit,=20 qapi_free_FOO() does nothing further than g_free(obj). But what happens in [4]? Here, the embedded dict was allocated, but we=20 then failed while parsing its members. That leaves us in a=20 partially-allocated state, and g_free(NULL) does NOT recursively visit=20 that partial allocation. I think this patch is prone to a memory leak=20 unless you _also_ patch things to free any dict branch on failure=20 (perhaps during the QTYPE_QDICT case label, rather than here at the end). --=20 Eric Blake, Principal Software Engineer Red Hat, Inc. +1-919-301-3226 Virtualization: qemu.org | libvirt.org