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89 lines
2.9 KiB
Diff
89 lines
2.9 KiB
Diff
From db29a9508a9246e77087c5531e45b2c88ec6988b Mon Sep 17 00:00:00 2001
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From: Florian Westphal <fw@strlen.de>
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Date: Fri, 26 Sep 2014 11:35:42 +0200
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Subject: [PATCH] netfilter: conntrack: disable generic tracking for known
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protocols
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Given following iptables ruleset:
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-P FORWARD DROP
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-A FORWARD -m sctp --dport 9 -j ACCEPT
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-A FORWARD -p tcp --dport 80 -j ACCEPT
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-A FORWARD -p tcp -m conntrack -m state ESTABLISHED,RELATED -j ACCEPT
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One would assume that this allows SCTP on port 9 and TCP on port 80.
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Unfortunately, if the SCTP conntrack module is not loaded, this allows
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*all* SCTP communication, to pass though, i.e. -p sctp -j ACCEPT,
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which we think is a security issue.
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This is because on the first SCTP packet on port 9, we create a dummy
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"generic l4" conntrack entry without any port information (since
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conntrack doesn't know how to extract this information).
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All subsequent packets that are unknown will then be in established
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state since they will fallback to proto_generic and will match the
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'generic' entry.
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Our originally proposed version [1] completely disabled generic protocol
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tracking, but Jozsef suggests to not track protocols for which a more
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suitable helper is available, hence we now mitigate the issue for in
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tree known ct protocol helpers only, so that at least NAT and direction
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information will still be preserved for others.
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[1] http://www.spinics.net/lists/netfilter-devel/msg33430.html
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Joint work with Daniel Borkmann.
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Signed-off-by: Florian Westphal <fw@strlen.de>
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Signed-off-by: Daniel Borkmann <dborkman@redhat.com>
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Acked-by: Jozsef Kadlecsik <kadlec@blackhole.kfki.hu>
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Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
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---
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net/netfilter/nf_conntrack_proto_generic.c | 26 +++++++++++++++++++++++++-
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1 file changed, 25 insertions(+), 1 deletion(-)
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diff --git a/net/netfilter/nf_conntrack_proto_generic.c b/net/netfilter/nf_conntrack_proto_generic.c
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index d25f293776482..957c1db666525 100644
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--- a/net/netfilter/nf_conntrack_proto_generic.c
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+++ b/net/netfilter/nf_conntrack_proto_generic.c
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@@ -14,6 +14,30 @@
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static unsigned int nf_ct_generic_timeout __read_mostly = 600*HZ;
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+static bool nf_generic_should_process(u8 proto)
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+{
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+ switch (proto) {
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+#ifdef CONFIG_NF_CT_PROTO_SCTP_MODULE
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+ case IPPROTO_SCTP:
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+ return false;
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+#endif
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+#ifdef CONFIG_NF_CT_PROTO_DCCP_MODULE
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+ case IPPROTO_DCCP:
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+ return false;
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+#endif
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+#ifdef CONFIG_NF_CT_PROTO_GRE_MODULE
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+ case IPPROTO_GRE:
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+ return false;
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+#endif
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+#ifdef CONFIG_NF_CT_PROTO_UDPLITE_MODULE
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+ case IPPROTO_UDPLITE:
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+ return false;
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+#endif
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+ default:
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+ return true;
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+ }
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+}
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+
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static inline struct nf_generic_net *generic_pernet(struct net *net)
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{
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return &net->ct.nf_ct_proto.generic;
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@@ -67,7 +91,7 @@ static int generic_packet(struct nf_conn *ct,
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static bool generic_new(struct nf_conn *ct, const struct sk_buff *skb,
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unsigned int dataoff, unsigned int *timeouts)
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{
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- return true;
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+ return nf_generic_should_process(nf_ct_protonum(ct));
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}
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#if IS_ENABLED(CONFIG_NF_CT_NETLINK_TIMEOUT)
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