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 050F4C7EE23 for ; Tue, 23 May 2023 13:04:23 +0000 (UTC) Received: from localhost ([::1] helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1q1Rg5-0003HN-7A; Tue, 23 May 2023 09:03:49 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1q1Rg3-0003Gr-18 for qemu-devel@nongnu.org; Tue, 23 May 2023 09:03:47 -0400 Received: from us-smtp-delivery-124.mimecast.com ([170.10.133.124]) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1q1Rg1-0000CH-1e for qemu-devel@nongnu.org; Tue, 23 May 2023 09:03:46 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1684847022; h=from:from:reply-to: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=gaSVe/ubveQ5cCN/BW/OiX+WXZA/Pko+U1uyj19xY+A=; b=Iemp9glofkT7hKHmYuL76PyErKA8UUxl99qTCHQGNqKjIRwWu/2qclrxmmrSktC3DpnqKR SLhCVYKlLHBQQ02wYfp/X1SsyueG7FETcuEka6UkB7GjvrfpAJhwpzltK7rVEOXLcFPLq3 2qMohu3NR58LcN7zQ5lWObYEbmW83nU= Received: from mimecast-mx02.redhat.com (mx3-rdu2.redhat.com [66.187.233.73]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-172-TwoyCvP8PZubBErDk_T_zw-1; Tue, 23 May 2023 09:02:32 -0400 X-MC-Unique: TwoyCvP8PZubBErDk_T_zw-1 Received: from smtp.corp.redhat.com (int-mx05.intmail.prod.int.rdu2.redhat.com [10.11.54.5]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id 47FD71C06ECB; Tue, 23 May 2023 13:02:30 +0000 (UTC) Received: from redhat.com (unknown [10.42.28.40]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 7BAB59D73; Tue, 23 May 2023 13:02:29 +0000 (UTC) Date: Tue, 23 May 2023 14:02:26 +0100 From: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= To: Mauro Matteo Cascella Cc: qemu-devel@nongnu.org, kraxel@redhat.com, marcandre.lureau@redhat.com, jacek.halon@gmail.com Subject: Re: [PATCH] ui/cursor: incomplete check for integer overflow in cursor_alloc Message-ID: References: <20230508141813.1086562-1-mcascell@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: User-Agent: Mutt/2.2.9 (2022-11-12) X-Scanned-By: MIMEDefang 3.1 on 10.11.54.5 Received-SPF: pass client-ip=170.10.133.124; envelope-from=berrange@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -20 X-Spam_score: -2.1 X-Spam_bar: -- X-Spam_report: (-2.1 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.001, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H2=-0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001, T_SCC_BODY_TEXT_LINE=-0.01 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: , Reply-To: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org On Tue, May 23, 2023 at 02:50:09PM +0200, Mauro Matteo Cascella wrote: > On Tue, May 23, 2023 at 10:16 AM Daniel P. Berrangé wrote: > > > > On Mon, May 08, 2023 at 04:18:13PM +0200, Mauro Matteo Cascella wrote: > > > The cursor_alloc function still accepts a signed integer for both the cursor > > > width and height. A specially crafted negative width/height could make datasize > > > wrap around and cause the next allocation to be 0, potentially leading to a > > > heap buffer overflow. Modify QEMUCursor struct and cursor_alloc prototype to > > > accept unsigned ints. > > > > > I concur with Marc-Andre that there is no code path that can > > actually trigger an overflow: > > > > > > hw/display/ati.c: s->cursor = cursor_alloc(64, 64); > > hw/display/vhost-user-gpu.c: s->current_cursor = cursor_alloc(64, 64); > > hw/display/virtio-gpu.c: s->current_cursor = cursor_alloc(64, 64); > > > > Not exploitable as fixed size > > > > hw/display/qxl-render.c: c = cursor_alloc(cursor->header.width, cursor->header.height); > > > > Cursor header defined as: > > > > typedef struct SPICE_ATTR_PACKED QXLCursorHeader { > > uint64_t unique; > > uint16_t type; > > uint16_t width; > > uint16_t height; > > uint16_t hot_spot_x; > > uint16_t hot_spot_y; > > } QXLCursorHeader; > > > > So no negative values can be passed to cursor_alloc() > > > > > Fixes: CVE-2023-1601 > > > Fixes: fa892e9a ("ui/cursor: fix integer overflow in cursor_alloc (CVE-2021-4206)") > > > > Given there is no possible codepath that can overflow, CVE-2023-1601 > > looks invalid to me. It should be clsoed as not-a-bug and these two > > Fixes lines removed. > > I think you can tweak the original PoC [1] to trigger this bug. > Setting width/height to 0x80000000 (versus 0x8000) should do the > trick. You should be able to overflow datasize while bypassing the > sanity check (width > 512 || height > 512) as width/height are signed > prior to this patch. I haven't tested it, though. The QXLCursorHeader width/height fields are uint16_t, so 0x80000000 will get truncated. No matter what value the guest sets, when we interpret this in qxl_cursor when calling cursor_alloc, the value will be in the range 0-65535, as that's the bounds of uint16_t. We'll pass this unsigned value to cursor_alloc() which converts from uint16_t, to (signed) int. 'int' is larger than uint16_t, so the result will still be positive in the range 0-65535, and so the sanity check > 512 will fire and protect us. I still see no bug, let alone a CVE. With regards, Daniel -- |: https://berrange.com -o- https://www.flickr.com/photos/dberrange :| |: https://libvirt.org -o- https://fstop138.berrange.com :| |: https://entangle-photo.org -o- https://www.instagram.com/dberrange :|