From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754078Ab1I1MUh (ORCPT ); Wed, 28 Sep 2011 08:20:37 -0400 Received: from mail-ey0-f174.google.com ([209.85.215.174]:62212 "EHLO mail-ey0-f174.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752997Ab1I1MUg (ORCPT ); Wed, 28 Sep 2011 08:20:36 -0400 Subject: Re: [PATCH 1/2] virtio-net: Verify page list size before fitting into skb From: Sasha Levin To: "Michael S. Tsirkin" Cc: linux-kernel@vger.kernel.org, Rusty Russell , virtualization@lists.linux-foundation.org, netdev@vger.kernel.org, kvm@vger.kernel.org In-Reply-To: <20110927123719.GB11276@redhat.com> References: <1317058869-19276-1-git-send-email-levinsasha928@gmail.com> <20110926184445.GA22278@redhat.com> <1317065842.20885.3.camel@lappy> <20110926195541.GA23086@redhat.com> <1317105842.3467.3.camel@lappy> <20110927070034.GB4690@redhat.com> <1317122429.3467.5.camel@lappy> <20110927123719.GB11276@redhat.com> Content-Type: text/plain; charset="us-ascii" Date: Wed, 28 Sep 2011 15:19:42 +0300 Message-ID: <1317212382.7213.21.camel@lappy> Mime-Version: 1.0 X-Mailer: Evolution 2.32.3 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, 2011-09-27 at 15:37 +0300, Michael S. Tsirkin wrote: > On Tue, Sep 27, 2011 at 02:20:29PM +0300, Sasha Levin wrote: > > On Tue, 2011-09-27 at 10:00 +0300, Michael S. Tsirkin wrote: > > > > skb = page_to_skb(vi, page, len); > > > > ... > > > > > > Sorry I don't get it yet. Where is mergeable ignored here? > > > > The NULL deref happens in page_to_skb(), before merge buffers are > > handled. > > The len here is a single buffer length, so for mergeable > buffers it is <= the size of the buffer we gave to hardware, > which is PAGE_SIZE. > > err = virtqueue_add_buf_single(vi->rvq, page_address(page), > PAGE_SIZE, false, page, gfp); > > > Unless of course we are trying to work around broken hardware again, > which I don't have a problem with, but should probably > get appropriate comments in code and trigger a warning. > > > I'll test it and see if it's really the case. I've verified it with VIRTIO_NET_F_MRG_RXBUF set, and we still get the NULL deref. -- Sasha.