From patchwork Sat Mar 12 10:14:42 2016 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Florian Westphal X-Patchwork-Id: 596640 X-Patchwork-Delegate: davem@davemloft.net Return-Path: X-Original-To: patchwork-incoming@ozlabs.org Delivered-To: patchwork-incoming@ozlabs.org Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by ozlabs.org (Postfix) with ESMTP id 3qMfy96LQ7z9sXQ for ; Sat, 12 Mar 2016 21:14:41 +1100 (AEDT) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751916AbcCLKOh (ORCPT ); Sat, 12 Mar 2016 05:14:37 -0500 Received: from Chamillionaire.breakpoint.cc ([80.244.247.6]:47664 "EHLO Chamillionaire.breakpoint.cc" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751241AbcCLKOf (ORCPT ); Sat, 12 Mar 2016 05:14:35 -0500 Received: from fw by Chamillionaire.breakpoint.cc with local (Exim 4.84) (envelope-from ) id 1aegZ4-0004Pf-Qk; Sat, 12 Mar 2016 11:14:31 +0100 From: Florian Westphal To: Cc: stephen@networkplumber.org, Florian Westphal , Felix Fietkau , Zefir Kurtisi Subject: [PATCH -next] bridge: fix potential use-after-free when hook returns QUEUE or STOLEN verdict Date: Sat, 12 Mar 2016 11:14:42 +0100 Message-Id: <1457777682-24689-1-git-send-email-fw@strlen.de> X-Mailer: git-send-email 2.4.10 Sender: netdev-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org Zefir Kurtisi reported kernel panic with an openwrt specific patch. However, it turns out that mainline has a similar bug waiting to happen. Once NF_HOOK() returns the skb is in undefined state and must not be used. Moreover, the okfn must consume the skb to support async processing (NF_QUEUE). Current okfn in this spot doesn't consume it and caller assumes that NF_HOOK return value tells us if skb was freed or not, but thats wrong. It "works" because no in-tree user registers a NFPROTO_BRIDGE hook at LOCAL_IN that returns STOLEN or NF_QUEUE verdicts. Once we add NF_QUEUE support for nftables bridge this will break -- NF_QUEUE holds the skb for async processing, caller will erronoulsy return RX_HANDLER_PASS and on reinject netfilter will access free'd skb. Fix this by pushing skb up the stack in the okfn instead. NB: It also seems dubious to use LOCAL_IN while bypassing PRE_ROUTING completely in this case but this is how its been forever so it seems preferable to not change this. Cc: Felix Fietkau Cc: Zefir Kurtisi Signed-off-by: Florian Westphal Tested-by: Zefir Kurtisi --- net/bridge/br_input.c | 16 +++++++--------- 1 file changed, 7 insertions(+), 9 deletions(-) diff --git a/net/bridge/br_input.c b/net/bridge/br_input.c index f7fba74..1607977 100644 --- a/net/bridge/br_input.c +++ b/net/bridge/br_input.c @@ -222,7 +222,10 @@ static int br_handle_local_finish(struct net *net, struct sock *sk, struct sk_bu /* check if vlan is allowed, to avoid spoofing */ if (p->flags & BR_LEARNING && br_should_learn(p, skb, &vid)) br_fdb_update(p->br, p, eth_hdr(skb)->h_source, vid, false); - return 0; /* process further */ + + BR_INPUT_SKB_CB(skb)->brdev = p->br->dev; + br_pass_frame_up(skb); + return 0; } /* @@ -284,14 +287,9 @@ rx_handler_result_t br_handle_frame(struct sk_buff **pskb) } /* Deliver packet to local host only */ - if (NF_HOOK(NFPROTO_BRIDGE, NF_BR_LOCAL_IN, - dev_net(skb->dev), NULL, skb, skb->dev, NULL, - br_handle_local_finish)) { - return RX_HANDLER_CONSUMED; /* consumed by filter */ - } else { - *pskb = skb; - return RX_HANDLER_PASS; /* continue processing */ - } + NF_HOOK(NFPROTO_BRIDGE, NF_BR_LOCAL_IN, dev_net(skb->dev), + NULL, skb, skb->dev, NULL, br_handle_local_finish); + return RX_HANDLER_CONSUMED; } forward: