netfilter: let reset rules clean out conntrack entries

iptables/nftables support responding to tcp packets with tcp resets.

The generated tcp reset packet passes through both output and postrouting
netfilter hooks, but conntrack will never see them because the generated
skb has its ->nfct pointer copied over from the packet that triggered the
reset rule.

If the reset rule is used for established connections, this
may result in the conntrack entry to be around for a very long
time (default timeout is 5 days).

One way to avoid this would be to not copy the nf_conn pointer
so that the rest packet passes through conntrack too.

Problem is that output rules might not have the same conntrack
zone setup as the prerouting ones, so its possible that the
reset skb won't find the correct entry.  Generating a template
entry for the skb seems error prone as well.

Add an explicit "closing" function that switches a confirmed
conntrack entry to closed state and wire this up for tcp.

If the entry isn't confirmed, no action is needed because
the conntrack entry will never be committed to the table.

Reported-by: Russel King <linux@armlinux.org.uk>
Signed-off-by: Florian Westphal <fw@strlen.de>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

diff --git a/include/linux/netfilter.h b/include/linux/netfilter.h
index d8817d381c14bfaecff3fb5a0b0cf487306e173a..6863e271a9deda135318f0b6b31b6b936bc84792 100644 (file)
--- a/include/linux/netfilter.h
+++ b/include/linux/netfilter.h
@@ -437,11 +437,13 @@ nf_nat_decode_session(struct sk_buff *skb, struct flowi *fl, u_int8_t family)
 #include <linux/netfilter/nf_conntrack_zones_common.h>
 
 void nf_ct_attach(struct sk_buff *, const struct sk_buff *);
+void nf_ct_set_closing(struct nf_conntrack *nfct);
 struct nf_conntrack_tuple;
 bool nf_ct_get_tuple_skb(struct nf_conntrack_tuple *dst_tuple,
                         const struct sk_buff *skb);
 #else
 static inline void nf_ct_attach(struct sk_buff *new, struct sk_buff *skb) {}
+static inline void nf_ct_set_closing(struct nf_conntrack *nfct) {}
 struct nf_conntrack_tuple;
 static inline bool nf_ct_get_tuple_skb(struct nf_conntrack_tuple *dst_tuple,
                                       const struct sk_buff *skb)
@@ -459,6 +461,7 @@ struct nf_ct_hook {
        bool (*get_tuple_skb)(struct nf_conntrack_tuple *,
                              const struct sk_buff *);
        void (*attach)(struct sk_buff *nskb, const struct sk_buff *skb);
+       void (*set_closing)(struct nf_conntrack *nfct);
 };
 extern const struct nf_ct_hook __rcu *nf_ct_hook;
 

diff --git a/include/net/netfilter/nf_conntrack.h b/include/net/netfilter/nf_conntrack.h
index 6a2019aaa46448be88b4994e5d41a07ce194a25f..3dbf947285be297ab4fbefc582edaccba88c33db 100644 (file)
--- a/include/net/netfilter/nf_conntrack.h
+++ b/include/net/netfilter/nf_conntrack.h
@@ -125,6 +125,12 @@ struct nf_conn {
        union nf_conntrack_proto proto;
 };
 
+static inline struct nf_conn *
+nf_ct_to_nf_conn(const struct nf_conntrack *nfct)
+{
+       return container_of(nfct, struct nf_conn, ct_general);
+}
+
 static inline struct nf_conn *
 nf_ct_tuplehash_to_ctrack(const struct nf_conntrack_tuple_hash *hash)
 {
@@ -175,6 +181,8 @@ nf_ct_get(const struct sk_buff *skb, enum ip_conntrack_info *ctinfo)
 
 void nf_ct_destroy(struct nf_conntrack *nfct);
 
+void nf_conntrack_tcp_set_closing(struct nf_conn *ct);
+
 /* decrement reference count on a conntrack */
 static inline void nf_ct_put(struct nf_conn *ct)
 {

diff --git a/net/ipv4/netfilter/nf_reject_ipv4.c b/net/ipv4/netfilter/nf_reject_ipv4.c
index d640adcaf1b125590ad60578c815b5a9ce20dfa2..f33aeab9424f75478aa19db46820823024762a0c 100644 (file)
--- a/net/ipv4/netfilter/nf_reject_ipv4.c
+++ b/net/ipv4/netfilter/nf_reject_ipv4.c
@@ -280,6 +280,7 @@ void nf_send_reset(struct net *net, struct sock *sk, struct sk_buff *oldskb,
                goto free_nskb;
 
        nf_ct_attach(nskb, oldskb);
+       nf_ct_set_closing(skb_nfct(oldskb));
 
 #if IS_ENABLED(CONFIG_BRIDGE_NETFILTER)
        /* If we use ip_local_out for bridged traffic, the MAC source on

diff --git a/net/ipv6/netfilter/nf_reject_ipv6.c b/net/ipv6/netfilter/nf_reject_ipv6.c
index f61d4f18e1cf51d227bf9e6538f120883335c0ff..58ccdb08c0fd1858f4fc5aa326d9efc5df935cba 100644 (file)
--- a/net/ipv6/netfilter/nf_reject_ipv6.c
+++ b/net/ipv6/netfilter/nf_reject_ipv6.c
@@ -345,6 +345,7 @@ void nf_send_reset6(struct net *net, struct sock *sk, struct sk_buff *oldskb,
        nf_reject_ip6_tcphdr_put(nskb, oldskb, otcph, otcplen);
 
        nf_ct_attach(nskb, oldskb);
+       nf_ct_set_closing(skb_nfct(oldskb));
 
 #if IS_ENABLED(CONFIG_BRIDGE_NETFILTER)
        /* If we use ip6_local_out for bridged traffic, the MAC source on

diff --git a/net/netfilter/core.c b/net/netfilter/core.c
index 5a6705a0e4ecf7e41d0100abe40b19ee18385359..b2fdbbed2b4b7a4167400cc5538bba2650e99cb0 100644 (file)
--- a/net/netfilter/core.c
+++ b/net/netfilter/core.c
@@ -702,6 +702,22 @@ void nf_conntrack_destroy(struct nf_conntrack *nfct)
 }
 EXPORT_SYMBOL(nf_conntrack_destroy);
 
+void nf_ct_set_closing(struct nf_conntrack *nfct)
+{
+       const struct nf_ct_hook *ct_hook;
+
+       if (!nfct)
+               return;
+
+       rcu_read_lock();
+       ct_hook = rcu_dereference(nf_ct_hook);
+       if (ct_hook)
+               ct_hook->set_closing(nfct);
+
+       rcu_read_unlock();
+}
+EXPORT_SYMBOL_GPL(nf_ct_set_closing);
+
 bool nf_ct_get_tuple_skb(struct nf_conntrack_tuple *dst_tuple,
                         const struct sk_buff *skb)
 {

diff --git a/net/netfilter/nf_conntrack_core.c b/net/netfilter/nf_conntrack_core.c
index c00858344f025f7dec964ab60e1e910506a9050a..430bb52b645492db05e7a872b7247684df9839ed 100644 (file)
--- a/net/netfilter/nf_conntrack_core.c
+++ b/net/netfilter/nf_conntrack_core.c
@@ -2747,11 +2747,23 @@ err_cachep:
        return ret;
 }
 
+static void nf_conntrack_set_closing(struct nf_conntrack *nfct)
+{
+       struct nf_conn *ct = nf_ct_to_nf_conn(nfct);
+
+       switch (nf_ct_protonum(ct)) {
+       case IPPROTO_TCP:
+               nf_conntrack_tcp_set_closing(ct);
+               break;
+       }
+}
+
 static const struct nf_ct_hook nf_conntrack_hook = {
        .update         = nf_conntrack_update,
        .destroy        = nf_ct_destroy,
        .get_tuple_skb  = nf_conntrack_get_tuple_skb,
        .attach         = nf_conntrack_attach,
+       .set_closing    = nf_conntrack_set_closing,
 };
 
 void nf_conntrack_init_end(void)

diff --git a/net/netfilter/nf_conntrack_proto_tcp.c b/net/netfilter/nf_conntrack_proto_tcp.c
index 16ee5ebe1ce15a799b74ecee7f2b68550cad5c95..4018acb1d674e1d50fa370427070f6cc5c3de737 100644 (file)
--- a/net/netfilter/nf_conntrack_proto_tcp.c
+++ b/net/netfilter/nf_conntrack_proto_tcp.c
@@ -911,6 +911,41 @@ static bool tcp_can_early_drop(const struct nf_conn *ct)
        return false;
 }
 
+void nf_conntrack_tcp_set_closing(struct nf_conn *ct)
+{
+       enum tcp_conntrack old_state;
+       const unsigned int *timeouts;
+       u32 timeout;
+
+       if (!nf_ct_is_confirmed(ct))
+               return;
+
+       spin_lock_bh(&ct->lock);
+       old_state = ct->proto.tcp.state;
+       ct->proto.tcp.state = TCP_CONNTRACK_CLOSE;
+
+       if (old_state == TCP_CONNTRACK_CLOSE ||
+           test_bit(IPS_FIXED_TIMEOUT_BIT, &ct->status)) {
+               spin_unlock_bh(&ct->lock);
+               return;
+       }
+
+       timeouts = nf_ct_timeout_lookup(ct);
+       if (!timeouts) {
+               const struct nf_tcp_net *tn;
+
+               tn = nf_tcp_pernet(nf_ct_net(ct));
+               timeouts = tn->timeouts;
+       }
+
+       timeout = timeouts[TCP_CONNTRACK_CLOSE];
+       WRITE_ONCE(ct->timeout, timeout + nfct_time_stamp);
+
+       spin_unlock_bh(&ct->lock);
+
+       nf_conntrack_event_cache(IPCT_PROTOINFO, ct);
+}
+
 static void nf_ct_tcp_state_reset(struct ip_ct_tcp_state *state)
 {
        state->td_end           = 0;