From patchwork Mon May 16 08:42:13 2022 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Jason Wang X-Patchwork-Id: 12850420 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 vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id D2930C433FE for ; Mon, 16 May 2022 08:42:43 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230264AbiEPImj (ORCPT ); Mon, 16 May 2022 04:42:39 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:43988 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S241857AbiEPImd (ORCPT ); Mon, 16 May 2022 04:42:33 -0400 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.133.124]) by lindbergh.monkeyblade.net (Postfix) with ESMTP id E46E4BC34 for ; Mon, 16 May 2022 01:42:27 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1652690547; h=from:from: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; bh=zsjSQ0E4x4apOOovvgvIeCzdF5L3Muj7tY5Ce1u0fFA=; b=HiMCBmcefGwx78a3Rgmxr8Jrj342i6wwNlIx8JWF50z4Yj0vNwEWiRy7NfOYaRkKhnqmEC sSMw3naw4qT9wFzSGCtKn1Kr8Ln/PGqolRkLRGONrnCclXvq2uxjwHMbtbg0EVQUX0zA4v ydE7nT6/Nu1boypEAzjNeWIPmzeiMyg= Received: from mimecast-mx02.redhat.com (mx3-rdu2.redhat.com [66.187.233.73]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-644-hrKwPFoVP6as52qPJiqDgw-1; Mon, 16 May 2022 04:42:20 -0400 X-MC-Unique: hrKwPFoVP6as52qPJiqDgw-1 Received: from smtp.corp.redhat.com (int-mx05.intmail.prod.int.rdu2.redhat.com [10.11.54.5]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id 4A4BF29AB44D; Mon, 16 May 2022 08:42:20 +0000 (UTC) Received: from localhost.localdomain (ovpn-13-125.pek2.redhat.com [10.72.13.125]) by smtp.corp.redhat.com (Postfix) with ESMTP id 6111A7C52; Mon, 16 May 2022 08:42:16 +0000 (UTC) From: Jason Wang To: viro@zeniv.linux.org.uk, mst@redhat.com, jasowang@redhat.com, kvm@vger.kernel.org Cc: virtualization@lists.linux-foundation.org, netdev@vger.kernel.org, linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org, ebiggers@kernel.org, davem@davemloft.net Subject: [PATCH] vhost_net: fix double fget() Date: Mon, 16 May 2022 16:42:13 +0800 Message-Id: <20220516084213.26854-1-jasowang@redhat.com> MIME-Version: 1.0 Content-type: text/plain X-Scanned-By: MIMEDefang 2.79 on 10.11.54.5 Precedence: bulk List-ID: X-Mailing-List: kvm@vger.kernel.org From: Al Viro Here's another piece of code assuming that repeated fget() will yield the same opened file: in vhost_net_set_backend() we have sock = get_socket(fd); if (IS_ERR(sock)) { r = PTR_ERR(sock); goto err_vq; } /* start polling new socket */ oldsock = vhost_vq_get_backend(vq); if (sock != oldsock) { ... vhost_vq_set_backend(vq, sock); ... if (index == VHOST_NET_VQ_RX) nvq->rx_ring = get_tap_ptr_ring(fd); with static struct socket *get_socket(int fd) { struct socket *sock; /* special case to disable backend */ if (fd == -1) return NULL; sock = get_raw_socket(fd); if (!IS_ERR(sock)) return sock; sock = get_tap_socket(fd); if (!IS_ERR(sock)) return sock; return ERR_PTR(-ENOTSOCK); } and static struct ptr_ring *get_tap_ptr_ring(int fd) { struct ptr_ring *ring; struct file *file = fget(fd); if (!file) return NULL; ring = tun_get_tx_ring(file); if (!IS_ERR(ring)) goto out; ring = tap_get_ptr_ring(file); if (!IS_ERR(ring)) goto out; ring = NULL; out: fput(file); return ring; } Again, there is no promise that fd will resolve to the same thing for lookups in get_socket() and in get_tap_ptr_ring(). I'm not familiar enough with the guts of drivers/vhost to tell how easy it is to turn into attack, but it looks like trouble. If nothing else, the pointer returned by tun_get_tx_ring() is not guaranteed to be pinned down by anything - the reference to sock will _usually_ suffice, but that doesn't help any if we get a different socket on that second fget(). One possible way to fix it would be the patch below; objections? Signed-off-by: Al Viro Signed-off-by: Jason Wang Acked-by: Michael S. Tsirkin Acked-by: Michael S. Tsirkin --- drivers/vhost/net.c | 15 +++++++-------- 1 file changed, 7 insertions(+), 8 deletions(-) diff --git a/drivers/vhost/net.c b/drivers/vhost/net.c index 28ef323882fb..0bd7d91de792 100644 --- a/drivers/vhost/net.c +++ b/drivers/vhost/net.c @@ -1449,13 +1449,9 @@ static struct socket *get_raw_socket(int fd) return ERR_PTR(r); } -static struct ptr_ring *get_tap_ptr_ring(int fd) +static struct ptr_ring *get_tap_ptr_ring(struct file *file) { struct ptr_ring *ring; - struct file *file = fget(fd); - - if (!file) - return NULL; ring = tun_get_tx_ring(file); if (!IS_ERR(ring)) goto out; @@ -1464,7 +1460,6 @@ static struct ptr_ring *get_tap_ptr_ring(int fd) goto out; ring = NULL; out: - fput(file); return ring; } @@ -1551,8 +1546,12 @@ static long vhost_net_set_backend(struct vhost_net *n, unsigned index, int fd) r = vhost_net_enable_vq(n, vq); if (r) goto err_used; - if (index == VHOST_NET_VQ_RX) - nvq->rx_ring = get_tap_ptr_ring(fd); + if (index == VHOST_NET_VQ_RX) { + if (sock) + nvq->rx_ring = get_tap_ptr_ring(sock->file); + else + nvq->rx_ring = NULL; + } oldubufs = nvq->ubufs; nvq->ubufs = ubufs;