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 606AFC44506 for ; Mon, 13 Jul 2026 10:08:15 +0000 (UTC) Received: from localhost ([::1] helo=lists1p.gnu.org) by lists1p.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1wjDa1-0000hO-La; Mon, 13 Jul 2026 06:08:05 -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 1wjDZy-0000gm-9I for qemu-devel@nongnu.org; Mon, 13 Jul 2026 06:08:03 -0400 Received: from us-smtp-delivery-124.mimecast.com ([170.10.129.124]) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1wjDZu-0006l2-53 for qemu-devel@nongnu.org; Mon, 13 Jul 2026 06:08:01 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1783937276; 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=SzmqswxmBb5euHwr1t3hKHm1YKJaitdYsaG92hlpL18=; b=VZEHNMcOaOn+WNkfNhk3S1DRa46Qs3c7AmHdTyYkmGZ0uLGCefZhV0ZbcTR084ITS6cVbS zK0KYrc5GrZWznahWN6dzi4TF7C9JisiZz2EHNnHZWxtRl9+K0C1ddh/Z9k0zIgEwQCFBL J08ChuxiZyKZ4FCp3QHwfcPZ76tnEb4= Received: from mx-prod-mc-08.mail-002.prod.us-west-2.aws.redhat.com (ec2-35-165-154-97.us-west-2.compute.amazonaws.com [35.165.154.97]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-655-gYKW8HeYMyazJGCsdeBXBA-1; Mon, 13 Jul 2026 06:07:54 -0400 X-MC-Unique: gYKW8HeYMyazJGCsdeBXBA-1 X-Mimecast-MFC-AGG-ID: gYKW8HeYMyazJGCsdeBXBA_1783937273 Received: from mx-prod-int-06.mail-002.prod.us-west-2.aws.redhat.com (mx-prod-int-06.mail-002.prod.us-west-2.aws.redhat.com [10.30.177.93]) (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-08.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id 8D5C318002C3 for ; Mon, 13 Jul 2026 10:07:53 +0000 (UTC) Received: from redhat.com (unknown [10.44.50.22]) by mx-prod-int-06.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id 53987180059F; Mon, 13 Jul 2026 10:07:51 +0000 (UTC) Date: Mon, 13 Jul 2026 11:07:48 +0100 From: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= To: marcandre.lureau@redhat.com Cc: qemu-devel@nongnu.org Subject: Re: [PATCH] ui/vnc: validate SetPixelFormat field ranges Message-ID: References: <20260713100056.4104383-1-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: <20260713100056.4104383-1-marcandre.lureau@redhat.com> User-Agent: Mutt/2.3.2 (2026-04-26) X-Scanned-By: MIMEDefang 3.4.1 on 10.30.177.93 Received-SPF: permerror client-ip=170.10.129.124; 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_H3=-0.01, RCVD_IN_MSPIKE_WL=-0.01, SPF_HELO_PASS=-0.001, T_SPF_PERMERROR=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: 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 Mon, Jul 13, 2026 at 02:00:56PM +0400, marcandre.lureau@redhat.com wrote: > From: Marc-André Lureau > > The VNC SetPixelFormat message carries red/green/blue_max as 16-bit > values, but PixelFormat stores them as uint8_t. A client sending a > max value above 255 (e.g. 0x0100) passes the existing non-zero check > but silently truncates to 0 on assignment, leading to a division by > zero in the Tight PNG palette path. > > Similarly, the shift values are read as uint8_t from the wire but > used in left-shift expressions (red_max << red_shift). Shifts >= 32 > are undefined behavior in C for 32-bit operands. > > Add explicit range checks for both: reject the connection if any > channel max exceeds UINT8_MAX, or any shift is >= 32. > > Fixes: CVE-2026-15578 > Resolves: https://gitlab.com/qemu-project/qemu/-/issues/3976 > Reported-by: dong ling > Signed-off-by: Marc-Andre Lureau > --- > ui/vnc.c | 10 ++++++++++ > 1 file changed, 10 insertions(+) Reviewed-by: Daniel P. Berrangé > > diff --git a/ui/vnc.c b/ui/vnc.c > index dfc8262d42a..c4ee4738b28 100644 > --- a/ui/vnc.c > +++ b/ui/vnc.c > @@ -2276,6 +2276,16 @@ static void set_pixel_format(VncState *vs, int bits_per_pixel, > return; > } > > + if (red_max > UINT8_MAX || green_max > UINT8_MAX || blue_max > UINT8_MAX) { > + vnc_client_error(vs); > + return; > + } > + > + if (red_shift >= 32 || green_shift >= 32 || blue_shift >= 32) { > + vnc_client_error(vs); > + return; > + } > + > vs->client_pf.rmax = red_max ? red_max : 0xFF; > vs->client_pf.rbits = ctpopl(red_max); > vs->client_pf.rshift = red_shift; 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 :|