From mboxrd@z Thu Jan 1 00:00:00 1970 From: Pablo Neira Ayuso Subject: [PATCH 6/8] netfilter: nf_ct_ext: fix possible panic after nf_ct_extend_unregister Date: Wed, 29 Mar 2017 14:14:08 +0200 Message-ID: <1490789650-7294-7-git-send-email-pablo@netfilter.org> References: <1490789650-7294-1-git-send-email-pablo@netfilter.org> Cc: davem@davemloft.net, netdev@vger.kernel.org To: netfilter-devel@vger.kernel.org Return-path: Received: from mail.us.es ([193.147.175.20]:43800 "EHLO mail.us.es" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756098AbdC2MPe (ORCPT ); Wed, 29 Mar 2017 08:15:34 -0400 Received: from antivirus1-rhel7.int (unknown [192.168.2.11]) by mail.us.es (Postfix) with ESMTP id 9E7F4EBAC9 for ; Wed, 29 Mar 2017 14:15:30 +0200 (CEST) Received: from antivirus1-rhel7.int (localhost [127.0.0.1]) by antivirus1-rhel7.int (Postfix) with ESMTP id 7D6E1DA391 for ; Wed, 29 Mar 2017 14:15:30 +0200 (CEST) Received: from antivirus1-rhel7.int (localhost [127.0.0.1]) by antivirus1-rhel7.int (Postfix) with ESMTP id 8E002DA8FF for ; Wed, 29 Mar 2017 14:15:26 +0200 (CEST) In-Reply-To: <1490789650-7294-1-git-send-email-pablo@netfilter.org> Sender: netdev-owner@vger.kernel.org List-ID: From: Liping Zhang If one cpu is doing nf_ct_extend_unregister while another cpu is doing __nf_ct_ext_add_length, then we may hit BUG_ON(t == NULL). Moreover, there's no synchronize_rcu invocation after set nf_ct_ext_types[id] to NULL, so it's possible that we may access invalid pointer. But actually, most of the ct extends are built-in, so the problem listed above will not happen. However, there are two exceptions: NF_CT_EXT_NAT and NF_CT_EXT_SYNPROXY. For _EXT_NAT, the panic will not happen, since adding the nat extend and unregistering the nat extend are located in the same file(nf_nat_core.c), this means that after the nat module is removed, we cannot add the nat extend too. For _EXT_SYNPROXY, synproxy extend may be added by init_conntrack, while synproxy extend unregister will be done by synproxy_core_exit. So after nf_synproxy_core.ko is removed, we may still try to add the synproxy extend, then kernel panic may happen. I know it's very hard to reproduce this issue, but I can play a tricky game to make it happen very easily :) Step 1. Enable SYNPROXY for tcp dport 1234 at FORWARD hook: # iptables -I FORWARD -p tcp --dport 1234 -j SYNPROXY Step 2. Queue the syn packet to the userspace at raw table OUTPUT hook. Also note, in the userspace we only add a 20s' delay, then reinject the syn packet to the kernel: # iptables -t raw -I OUTPUT -p tcp --syn -j NFQUEUE --queue-num 1 Step 3. Using "nc 2.2.2.2 1234" to connect the server. Step 4. Now remove the nf_synproxy_core.ko quickly: # iptables -F FORWARD # rmmod ipt_SYNPROXY # rmmod nf_synproxy_core Step 5. After 20s' delay, the syn packet is reinjected to the kernel. Now you will see the panic like this: kernel BUG at net/netfilter/nf_conntrack_extend.c:91! Call Trace: ? __nf_ct_ext_add_length+0x53/0x3c0 [nf_conntrack] init_conntrack+0x12b/0x600 [nf_conntrack] nf_conntrack_in+0x4cc/0x580 [nf_conntrack] ipv4_conntrack_local+0x48/0x50 [nf_conntrack_ipv4] nf_reinject+0x104/0x270 nfqnl_recv_verdict+0x3e1/0x5f9 [nfnetlink_queue] ? nfqnl_recv_verdict+0x5/0x5f9 [nfnetlink_queue] ? nla_parse+0xa0/0x100 nfnetlink_rcv_msg+0x175/0x6a9 [nfnetlink] [...] One possible solution is to make NF_CT_EXT_SYNPROXY extend built-in, i.e. introduce nf_conntrack_synproxy.c and only do ct extend register and unregister in it, similar to nf_conntrack_timeout.c. But having such a obscure restriction of nf_ct_extend_unregister is not a good idea, so we should invoke synchronize_rcu after set nf_ct_ext_types to NULL, and check the NULL pointer when do __nf_ct_ext_add_length. Then it will be easier if we add new ct extend in the future. Last, we use kfree_rcu to free nf_ct_ext, so rcu_barrier() is unnecessary anymore, remove it too. Signed-off-by: Liping Zhang Acked-by: Florian Westphal Signed-off-by: Pablo Neira Ayuso --- net/netfilter/nf_conntrack_extend.c | 13 ++++++++++--- 1 file changed, 10 insertions(+), 3 deletions(-) diff --git a/net/netfilter/nf_conntrack_extend.c b/net/netfilter/nf_conntrack_extend.c index 02bcf00c2492..008299b7f78f 100644 --- a/net/netfilter/nf_conntrack_extend.c +++ b/net/netfilter/nf_conntrack_extend.c @@ -53,7 +53,11 @@ nf_ct_ext_create(struct nf_ct_ext **ext, enum nf_ct_ext_id id, rcu_read_lock(); t = rcu_dereference(nf_ct_ext_types[id]); - BUG_ON(t == NULL); + if (!t) { + rcu_read_unlock(); + return NULL; + } + off = ALIGN(sizeof(struct nf_ct_ext), t->align); len = off + t->len + var_alloc_len; alloc_size = t->alloc_size + var_alloc_len; @@ -88,7 +92,10 @@ void *__nf_ct_ext_add_length(struct nf_conn *ct, enum nf_ct_ext_id id, rcu_read_lock(); t = rcu_dereference(nf_ct_ext_types[id]); - BUG_ON(t == NULL); + if (!t) { + rcu_read_unlock(); + return NULL; + } newoff = ALIGN(old->len, t->align); newlen = newoff + t->len + var_alloc_len; @@ -175,6 +182,6 @@ void nf_ct_extend_unregister(struct nf_ct_ext_type *type) RCU_INIT_POINTER(nf_ct_ext_types[type->id], NULL); update_alloc_size(type); mutex_unlock(&nf_ct_ext_type_mutex); - rcu_barrier(); /* Wait for completion of call_rcu()'s */ + synchronize_rcu(); } EXPORT_SYMBOL_GPL(nf_ct_extend_unregister); -- 2.1.4