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 lists1p.gnu.org (lists1p.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 1903AC61DC2 for ; Thu, 27 Aug 2026 10:30:56 +0000 (UTC) Received: from localhost ([::1] helo=lists1p.gnu.org) by lists1p.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1wzXNJ-0001Al-IC; Thu, 27 Aug 2026 06:30:25 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]) by lists1p.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1wzXNG-0001AI-U8 for qemu-devel@nongnu.org; Thu, 27 Aug 2026 06:30:22 -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 1wzXNF-0005e5-5M for qemu-devel@nongnu.org; Thu, 27 Aug 2026 06:30:22 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1787826619; 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=Ch+c0lIYIhs4oj0KT3rgvce0AE/PdcU0D0NmHIz2grc=; b=cYwXqnc3kA7nYSllFlihhJk8fq1P1LKCZff8wO9ANY4egDxtIbM0OYACTrAqu13UVFV8CV B30jRTPqg8YcM6aGNT4Bh3k5x2JC1Xkj/YxZpXVMfZpje3Hw5Hs4lf2JFQAK0akiTRBB+f YSPt/0svJ/OLKaJRVdvybnZ5FTw4beQ= Received: from mx-prod-mc-03.mail-002.prod.us-west-2.aws.redhat.com (ec2-54-186-198-63.us-west-2.compute.amazonaws.com [54.186.198.63]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-146-haeoymO-PvqiTY9VuKSMHg-1; Thu, 27 Aug 2026 06:30:16 -0400 X-MC-Unique: haeoymO-PvqiTY9VuKSMHg-1 X-Mimecast-MFC-AGG-ID: haeoymO-PvqiTY9VuKSMHg_1787826615 Received: from mx-prod-int-03.mail-002.prod.us-west-2.aws.redhat.com (mx-prod-int-03.mail-002.prod.us-west-2.aws.redhat.com [10.30.177.12]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest SHA256) (No client certificate requested) by mx-prod-mc-03.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id AEE061955F1D; Thu, 27 Aug 2026 10:30:15 +0000 (UTC) Received: from redhat.com (headnet05.pony-001.prod.iad2.dc.redhat.com [10.2.32.117]) by mx-prod-int-03.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id 8B8411955F04; Thu, 27 Aug 2026 10:30:14 +0000 (UTC) Date: Thu, 27 Aug 2026 11:30:11 +0100 From: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= To: =?utf-8?Q?Marc-Andr=C3=A9?= Lureau Cc: qemu-devel@nongnu.org, akihiko.odaki@gmail.com Subject: Re: [PATCH] ui/console: fix use-after-free in qemu_console_set_cursor Message-ID: References: <20260827070647.2872650-1-marcandre.lureau@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/2.4.0 (2026-06-19) X-Scanned-By: MIMEDefang 3.0 on 10.30.177.12 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: 12 X-Spam_score: 1.2 X-Spam_bar: + X-Spam_report: (1.2 / 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_H3=0.001, RCVD_IN_MSPIKE_WL=0.001, RCVD_IN_SBL_CSS=3.335, SPF_HELO_PASS=-0.001, SPF_PASS=-0.001 autolearn=no autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: qemu development 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 Thu, Aug 27, 2026 at 01:58:14PM +0400, Marc-André Lureau wrote: > Hi > > On Thu, Aug 27, 2026 at 12:47 PM Daniel P. Berrangé wrote: > > > > On Thu, Aug 27, 2026 at 11:06:47AM +0400, marcandre.lureau@redhat.com wrote: > > > From: Marc-André Lureau > > > > > > When the new cursor is the same object as the one already held by > > > the console and the refcount is 1, cursor_unref frees it before > > > cursor_ref can increment the count. > > > > > > Ref the incoming cursor before unreffing the old one so the > > > refcount goes 1-2-1 instead of 1-0 (freed) then use-after-free. > > > > I don't see where/how this can happen. The caller of > > qemu_console_set_cursor should own its own reference > > on 'cursor'. So on entry to this method, 'cursor' > > should have a ref of 2 if it is the same as the > > current con->cursor. > > > > if anything the behaviour you describe sounds like a > > bug in a caller not holding its own reference. > > You are right, I thought virtio-gpu kept a weak pointer, but it should > have a strong ref, so we should never reach 0. I can't explain the > crash I observed then. Is there a bug report for this or crash scenario info ? Something wrong with the 'cursor' object stored in virtio_gpu_scanout ? I notice in the VMState: VMSTATE_UINT32(cursor.resource_id, struct virtio_gpu_scanout), VMSTATE_UINT32(cursor.hot_x, struct virtio_gpu_scanout), VMSTATE_UINT32(cursor.hot_y, struct virtio_gpu_scanout), VMSTATE_UINT32(cursor.pos.x, struct virtio_gpu_scanout), VMSTATE_UINT32(cursor.pos.y, struct virtio_gpu_scanout), what is restoring the "refcount" to "1" when vmstate is loaded ? With regards, Daniel -- |: https://berrange.com ~~ https://hachyderm.io/@berrange :| |: https://libvirt.org ~~ https://entangle-photo.org :| |: https://pixelfed.art/berrange ~~ https://fstop138.berrange.com :|