From 1025ce75212bf06d93910297a03ed6a4d41d8213 Mon Sep 17 00:00:00 2001 From: Florian Westphal Date: Mon, 25 Mar 2019 23:11:54 +0100 Subject: netfilter: conntrack: don't set related state for different outer address Luca Moro says: ------ The issue lies in the filtering of ICMP and ICMPv6 errors that include an inner IP datagram. For these packets, icmp_error_message() extract the ICMP error and inner layer to search of a known state. If a state is found the packet is tagged as related (IP_CT_RELATED). The problem is that there is no correlation check between the inner and outer layer of the packet. So one can encapsulate an error with an inner layer matching a known state, while its outer layer is directed to a filtered host. In this case the whole packet will be tagged as related. This has various implications from a rule bypass (if a rule to related trafic is allow), to a known state oracle. Unfortunately, we could not find a real statement in a RFC on how this case should be filtered. The closest we found is RFC5927 (Section 4.3) but it is not very clear. A possible fix would be to check that the inner IP source is the same than the outer destination. We believed this kind of attack was not documented yet, so we started to write a blog post about it. You can find it attached to this mail (sorry for the extract quality). It contains more technical details, PoC and discussion about the identified behavior. We discovered later that https://www.gont.com.ar/papers/filtering-of-icmp-error-messages.pdf described a similar attack concept in 2004 but without the stateful filtering in mind. ----- This implements above suggested fix: In icmp(v6) error handler, take outer destination address, then pass that into the common function that does the "related" association. After obtaining the nf_conn of the matching inner-headers connection, check that the destination address of the opposite direction tuple is the same as the outer address and only set RELATED if thats the case. Reported-by: Luca Moro Signed-off-by: Florian Westphal Signed-off-by: Pablo Neira Ayuso --- include/net/netfilter/nf_conntrack_l4proto.h | 6 ++++++ 1 file changed, 6 insertions(+) (limited to 'include') diff --git a/include/net/netfilter/nf_conntrack_l4proto.h b/include/net/netfilter/nf_conntrack_l4proto.h index 778087591983..a49edfdf47e8 100644 --- a/include/net/netfilter/nf_conntrack_l4proto.h +++ b/include/net/netfilter/nf_conntrack_l4proto.h @@ -75,6 +75,12 @@ bool nf_conntrack_invert_icmp_tuple(struct nf_conntrack_tuple *tuple, bool nf_conntrack_invert_icmpv6_tuple(struct nf_conntrack_tuple *tuple, const struct nf_conntrack_tuple *orig); +int nf_conntrack_inet_error(struct nf_conn *tmpl, struct sk_buff *skb, + unsigned int dataoff, + const struct nf_hook_state *state, + u8 l4proto, + union nf_inet_addr *outer_daddr); + int nf_conntrack_icmpv4_error(struct nf_conn *tmpl, struct sk_buff *skb, unsigned int dataoff, -- cgit v1.2.3 From 3c79107631db1f7fd32cf3f7368e4672004a3010 Mon Sep 17 00:00:00 2001 From: Florian Westphal Date: Mon, 1 Apr 2019 13:08:54 +0200 Subject: netfilter: ctnetlink: don't use conntrack/expect object addresses as id else, we leak the addresses to userspace via ctnetlink events and dumps. Compute an ID on demand based on the immutable parts of nf_conn struct. Another advantage compared to using an address is that there is no immediate re-use of the same ID in case the conntrack entry is freed and reallocated again immediately. Fixes: 3583240249ef ("[NETFILTER]: nf_conntrack_expect: kill unique ID") Fixes: 7f85f914721f ("[NETFILTER]: nf_conntrack: kill unique ID") Signed-off-by: Florian Westphal Signed-off-by: Pablo Neira Ayuso --- include/net/netfilter/nf_conntrack.h | 2 ++ 1 file changed, 2 insertions(+) (limited to 'include') diff --git a/include/net/netfilter/nf_conntrack.h b/include/net/netfilter/nf_conntrack.h index 5ee7b30b4917..d2bc733a2ef1 100644 --- a/include/net/netfilter/nf_conntrack.h +++ b/include/net/netfilter/nf_conntrack.h @@ -316,6 +316,8 @@ struct nf_conn *nf_ct_tmpl_alloc(struct net *net, gfp_t flags); void nf_ct_tmpl_free(struct nf_conn *tmpl); +u32 nf_ct_get_id(const struct nf_conn *ct); + static inline void nf_ct_set(struct sk_buff *skb, struct nf_conn *ct, enum ip_conntrack_info info) { -- cgit v1.2.3