From mboxrd@z Thu Jan 1 00:00:00 1970 From: Florian Westphal Subject: [PATCH nf] netfilter: sync with packet rx also after removing queue entries Date: Thu, 8 Oct 2015 23:38:07 +0200 Message-ID: <1444340287-8779-1-git-send-email-fw@strlen.de> Cc: Florian Westphal , "Eric W. Biederman" To: Return-path: Received: from Chamillionaire.breakpoint.cc ([80.244.247.6]:37858 "EHLO Chamillionaire.breakpoint.cc" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755976AbbJHViR (ORCPT ); Thu, 8 Oct 2015 17:38:17 -0400 Sender: netfilter-devel-owner@vger.kernel.org List-ID: We need to sync packet rx again after flushing the queue entries. Otherwise, the following race could happen: cpu1: nf_unregister_hook(H) called, H unliked from lists, calls synchronize_net() to wait for packet rx completion. Problem is that while no new nf_queue_entry structs that use H can be allocated, another CPU might receive a verdict from userspace just before cpu1 calls nf_queue_nf_hook_drop to remove this entry: cpu2: receive verdict from userspace, lock queue cpu2: unlink nf_queue_entry struct E, which references H, from queue list cpu1: calls nf_queue_nf_hook_drop, blocks on queue spinlock cpu2: unlock queue cpu1: nf_queue_nf_hook_drop drops affected queue entries cpu2: call nf_reinject for E cpu1: kfree(H) cpu2: potential use-after-free for H Cc: Eric W. Biederman Fixes: 085db2c04557 ("netfilter: Per network namespace netfilter hooks.") Signed-off-by: Florian Westphal --- Found during code review, no actual panic was observed. diff --git a/net/netfilter/core.c b/net/netfilter/core.c index 8e47f81..21a0856 100644 --- a/net/netfilter/core.c +++ b/net/netfilter/core.c @@ -152,6 +152,8 @@ void nf_unregister_net_hook(struct net *net, const struct nf_hook_ops *reg) #endif synchronize_net(); nf_queue_nf_hook_drop(net, &entry->ops); + /* other cpu might still process nfqueue verdict that used reg */ + synchronize_net(); kfree(entry); } EXPORT_SYMBOL(nf_unregister_net_hook); -- 2.0.5