From patchwork Thu Apr 25 07:33:19 2019 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Jason Wang X-Patchwork-Id: 10916185 Return-Path: Received: from mail.wl.linuxfoundation.org (pdx-wl-mail.web.codeaurora.org [172.30.200.125]) by pdx-korg-patchwork-2.web.codeaurora.org (Postfix) with ESMTP id E4F501575 for ; Thu, 25 Apr 2019 07:33:33 +0000 (UTC) Received: from mail.wl.linuxfoundation.org (localhost [127.0.0.1]) by mail.wl.linuxfoundation.org (Postfix) with ESMTP id D276828BD7 for ; Thu, 25 Apr 2019 07:33:33 +0000 (UTC) Received: by mail.wl.linuxfoundation.org (Postfix, from userid 486) id C64AC28BE1; Thu, 25 Apr 2019 07:33:33 +0000 (UTC) X-Spam-Checker-Version: SpamAssassin 3.3.1 (2010-03-16) on pdx-wl-mail.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-7.9 required=2.0 tests=BAYES_00,MAILING_LIST_MULTI, RCVD_IN_DNSWL_HI autolearn=ham version=3.3.1 Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.wl.linuxfoundation.org (Postfix) with ESMTP id 590B228BD7 for ; Thu, 25 Apr 2019 07:33:33 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726957AbfDYHd1 (ORCPT ); Thu, 25 Apr 2019 03:33:27 -0400 Received: from mx1.redhat.com ([209.132.183.28]:60130 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726317AbfDYHd1 (ORCPT ); Thu, 25 Apr 2019 03:33:27 -0400 Received: from smtp.corp.redhat.com (int-mx07.intmail.prod.int.phx2.redhat.com [10.5.11.22]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id C2BCE3002619; Thu, 25 Apr 2019 07:33:26 +0000 (UTC) Received: from hp-dl380pg8-02.lab.eng.pek2.redhat.com (hp-dl380pg8-02.lab.eng.pek2.redhat.com [10.73.8.12]) by smtp.corp.redhat.com (Postfix) with ESMTP id 5DA021001DDB; Thu, 25 Apr 2019 07:33:21 +0000 (UTC) From: Jason Wang To: mst@redhat.com, jasowang@redhat.com, kvm@vger.kernel.org, virtualization@lists.linux-foundation.org, netdev@vger.kernel.org, linux-kernel@vger.kernel.org Cc: ppandit@redhat.com Subject: [PATCH net] vhost_net: fix possible infinite loop Date: Thu, 25 Apr 2019 03:33:19 -0400 Message-Id: <1556177599-56248-1-git-send-email-jasowang@redhat.com> X-Scanned-By: MIMEDefang 2.84 on 10.5.11.22 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.40]); Thu, 25 Apr 2019 07:33:26 +0000 (UTC) Sender: kvm-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: kvm@vger.kernel.org X-Virus-Scanned: ClamAV using ClamSMTP When the rx buffer is too small for a packet, we will discard the vq descriptor and retry it for the next packet: while ((sock_len = vhost_net_rx_peek_head_len(net, sock->sk, &busyloop_intr))) { ... /* On overrun, truncate and discard */ if (unlikely(headcount > UIO_MAXIOV)) { iov_iter_init(&msg.msg_iter, READ, vq->iov, 1, 1); err = sock->ops->recvmsg(sock, &msg, 1, MSG_DONTWAIT | MSG_TRUNC); pr_debug("Discarded rx packet: len %zd\n", sock_len); continue; } ... } This makes it possible to trigger a infinite while..continue loop through the co-opreation of two VMs like: 1) Malicious VM1 allocate 1 byte rx buffer and try to slow down the vhost process as much as possible e.g using indirect descriptors or other. 2) Malicious VM2 generate packets to VM1 as fast as possible Fixing this by checking against weight at the end of RX and TX loop. This also eliminate other similar cases when: - userspace is consuming the packets in the meanwhile - theoretical TOCTOU attack if guest moving avail index back and forth to hit the continue after vhost find guest just add new buffers This addresses CVE-2019-3900. Fixes: d8316f3991d20 ("vhost: fix total length when packets are too short") Fixes: 3a4d5c94e9593 ("vhost_net: a kernel-level virtio server") Signed-off-by: Jason Wang --- drivers/vhost/net.c | 41 +++++++++++++++++++++-------------------- 1 file changed, 21 insertions(+), 20 deletions(-) diff --git a/drivers/vhost/net.c b/drivers/vhost/net.c index df51a35..fb46e6b 100644 --- a/drivers/vhost/net.c +++ b/drivers/vhost/net.c @@ -778,8 +778,9 @@ static void handle_tx_copy(struct vhost_net *net, struct socket *sock) int err; int sent_pkts = 0; bool sock_can_batch = (sock->sk->sk_sndbuf == INT_MAX); + bool next_round = false; - for (;;) { + do { bool busyloop_intr = false; if (nvq->done_idx == VHOST_NET_BATCH) @@ -845,11 +846,10 @@ static void handle_tx_copy(struct vhost_net *net, struct socket *sock) vq->heads[nvq->done_idx].id = cpu_to_vhost32(vq, head); vq->heads[nvq->done_idx].len = 0; ++nvq->done_idx; - if (vhost_exceeds_weight(++sent_pkts, total_len)) { - vhost_poll_queue(&vq->poll); - break; - } - } + } while (!(next_round = vhost_exceeds_weight(++sent_pkts, total_len))); + + if (next_round) + vhost_poll_queue(&vq->poll); vhost_tx_batch(net, nvq, sock, &msg); } @@ -873,8 +873,9 @@ static void handle_tx_zerocopy(struct vhost_net *net, struct socket *sock) struct vhost_net_ubuf_ref *uninitialized_var(ubufs); bool zcopy_used; int sent_pkts = 0; + bool next_round = false; - for (;;) { + do { bool busyloop_intr; /* Release DMAs done buffers first */ @@ -951,11 +952,10 @@ static void handle_tx_zerocopy(struct vhost_net *net, struct socket *sock) else vhost_zerocopy_signal_used(net, vq); vhost_net_tx_packet(net); - if (unlikely(vhost_exceeds_weight(++sent_pkts, total_len))) { - vhost_poll_queue(&vq->poll); - break; - } - } + } while (!(next_round = vhost_exceeds_weight(++sent_pkts, total_len))); + + if (next_round) + vhost_poll_queue(&vq->poll); } /* Expects to be always run from workqueue - which acts as @@ -1134,6 +1134,7 @@ static void handle_rx(struct vhost_net *net) struct iov_iter fixup; __virtio16 num_buffers; int recv_pkts = 0; + bool next_round = false; mutex_lock_nested(&vq->mutex, VHOST_NET_VQ_RX); sock = vq->private_data; @@ -1153,8 +1154,11 @@ static void handle_rx(struct vhost_net *net) vq->log : NULL; mergeable = vhost_has_feature(vq, VIRTIO_NET_F_MRG_RXBUF); - while ((sock_len = vhost_net_rx_peek_head_len(net, sock->sk, - &busyloop_intr))) { + do { + sock_len = vhost_net_rx_peek_head_len(net, sock->sk, + &busyloop_intr); + if (!sock_len) + break; sock_len += sock_hlen; vhost_len = sock_len + vhost_hlen; headcount = get_rx_bufs(vq, vq->heads + nvq->done_idx, @@ -1239,12 +1243,9 @@ static void handle_rx(struct vhost_net *net) vhost_log_write(vq, vq_log, log, vhost_len, vq->iov, in); total_len += vhost_len; - if (unlikely(vhost_exceeds_weight(++recv_pkts, total_len))) { - vhost_poll_queue(&vq->poll); - goto out; - } - } - if (unlikely(busyloop_intr)) + } while (!(next_round = vhost_exceeds_weight(++recv_pkts, total_len))); + + if (unlikely(busyloop_intr || next_round)) vhost_poll_queue(&vq->poll); else vhost_net_enable_vq(net, vq);