From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:37515) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1cGl5g-0004tr-N0 for qemu-devel@nongnu.org; Tue, 13 Dec 2016 06:17:49 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1cGl5b-0005yf-Mg for qemu-devel@nongnu.org; Tue, 13 Dec 2016 06:17:48 -0500 Received: from mx1.redhat.com ([209.132.183.28]:57594) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1cGl5b-0005xn-HA for qemu-devel@nongnu.org; Tue, 13 Dec 2016 06:17:43 -0500 Message-ID: <1481627861.27088.116.camel@redhat.com> From: Gerd Hoffmann Date: Tue, 13 Dec 2016 12:17:41 +0100 In-Reply-To: <20161213071439.32322-1-ppandit@redhat.com> References: <20161213071439.32322-1-ppandit@redhat.com> Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable Mime-Version: 1.0 Subject: Re: [Qemu-devel] [PATCH] display: virtio-gpu-3d: check virgl capabilities max_size List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: P J P Cc: Qemu Developers , Zhenhao Hong , Prasad J Pandit On Di, 2016-12-13 at 12:44 +0530, P J P wrote: > From: Prasad J Pandit >=20 > Virtio GPU device while processing 'VIRTIO_GPU_CMD_GET_CAPSET' > command, retrieves the maximum capabilities size to fill in the > response object. It continues to fill in capabilities even if > retrieved 'max_size' is zero(0), thus resulting in OOB access. > Add check to avoid it. Hmm? Did you see this happing in practice? > diff --git a/hw/display/virtio-gpu-3d.c b/hw/display/virtio-gpu-3d.c > index 758d33a..fbfb39f 100644 > --- a/hw/display/virtio-gpu-3d.c > +++ b/hw/display/virtio-gpu-3d.c > @@ -371,11 +371,12 @@ static void virgl_cmd_get_capset(VirtIOGPU *g, > virgl_renderer_get_cap_set(gc.capset_id, &max_ver, > &max_size); This is not the guest returning the size, it is the host renderer library saying how much space it needs ... > resp =3D g_malloc(sizeof(*resp) + max_size); > - > - resp->hdr.type =3D VIRTIO_GPU_RESP_OK_CAPSET; > - virgl_renderer_fill_caps(gc.capset_id, > - gc.capset_version, > - (void *)resp->capset_data); ... and here the renderer fills the qemu-allocated space with the actual data. Can't see anything wrong here. It's not that we process untrusted data without checking. If a buffer overflow happens here this would clearly be a bug in the virglrenderer library, because the size advertised and the size actually needed mismatch. cheers, Gerd