[PATCH nf-next 1/4] netfilter: conntrack: __nf_ct_l4proto_find() always returns valid pointer

[PATCH nf-next 1/4] netfilter: conntrack: __nf_ct_l4proto_find() always returns valid pointer

[Pablo Neira Ayuso]

Remove unnecessary check for non-nul pointer in destroy_conntrack()
given that __nf_ct_l4proto_find() returns the generic protocol tracker
if the protocol is not supported.

Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
---
 net/netfilter/nf_conntrack_core.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/net/netfilter/nf_conntrack_core.c b/net/netfilter/nf_conntrack_core.c
index 1fd0ff1..32fba4f 100644
--- a/net/netfilter/nf_conntrack_core.c
+++ b/net/netfilter/nf_conntrack_core.c
@@ -360,7 +360,7 @@ destroy_conntrack(struct nf_conntrack *nfct)
 	}
 	rcu_read_lock();
 	l4proto = __nf_ct_l4proto_find(nf_ct_l3num(ct), nf_ct_protonum(ct));
-	if (l4proto && l4proto->destroy)
+	if (l4proto->destroy)
 		l4proto->destroy(ct);
 
 	rcu_read_unlock();
-- 
2.1.4

[PATCH nf-next 2/4] netfilter: conntrack: introduce nf_ct_acct_update()

[Pablo Neira Ayuso]

Introduce a helper function to update conntrack counters.
__nf_ct_kill_acct() was unnecessarily subtracting skb_network_offset()
that is expected to be zero from the ipv4/ipv6 hooks.

Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
---
 net/netfilter/nf_conntrack_core.c | 42 ++++++++++++++++++---------------------
 1 file changed, 19 insertions(+), 23 deletions(-)

diff --git a/net/netfilter/nf_conntrack_core.c b/net/netfilter/nf_conntrack_core.c
index 32fba4f..8462b54 100644
--- a/net/netfilter/nf_conntrack_core.c
+++ b/net/netfilter/nf_conntrack_core.c
@@ -601,6 +601,21 @@ out:
 }
 EXPORT_SYMBOL_GPL(nf_conntrack_hash_check_insert);
 
+static inline void nf_ct_acct_update(struct nf_conn *ct,
+				     enum ip_conntrack_info ctinfo,
+				     unsigned int len)
+{
+	struct nf_conn_acct *acct;
+
+	acct = nf_conn_acct_find(ct);
+	if (acct) {
+		struct nf_conn_counter *counter = acct->counter;
+
+		atomic64_inc(&counter[CTINFO2DIR(ctinfo)].packets);
+		atomic64_add(len, &counter[CTINFO2DIR(ctinfo)].bytes);
+	}
+}
+
 /* Confirm a connection given skb; places it in hash table */
 int
 __nf_conntrack_confirm(struct sk_buff *skb)
@@ -1251,17 +1266,8 @@ void __nf_ct_refresh_acct(struct nf_conn *ct,
 	}
 
 acct:
-	if (do_acct) {
-		struct nf_conn_acct *acct;
-
-		acct = nf_conn_acct_find(ct);
-		if (acct) {
-			struct nf_conn_counter *counter = acct->counter;
-
-			atomic64_inc(&counter[CTINFO2DIR(ctinfo)].packets);
-			atomic64_add(skb->len, &counter[CTINFO2DIR(ctinfo)].bytes);
-		}
-	}
+	if (do_acct)
+		nf_ct_acct_update(ct, ctinfo, skb->len);
 }
 EXPORT_SYMBOL_GPL(__nf_ct_refresh_acct);
 
@@ -1270,18 +1276,8 @@ bool __nf_ct_kill_acct(struct nf_conn *ct,
 		       const struct sk_buff *skb,
 		       int do_acct)
 {
-	if (do_acct) {
-		struct nf_conn_acct *acct;
-
-		acct = nf_conn_acct_find(ct);
-		if (acct) {
-			struct nf_conn_counter *counter = acct->counter;
-
-			atomic64_inc(&counter[CTINFO2DIR(ctinfo)].packets);
-			atomic64_add(skb->len - skb_network_offset(skb),
-				     &counter[CTINFO2DIR(ctinfo)].bytes);
-		}
-	}
+	if (do_acct)
+		nf_ct_acct_update(ct, ctinfo, skb->len);
 
 	if (del_timer(&ct->timeout)) {
 		ct->timeout.function((unsigned long)ct);
-- 
2.1.4

[PATCH nf-next 3/4] netfilter: conntrack: introduce clash resolution on insertion race

[Pablo Neira Ayuso]

This patch introduces nf_ct_resolve_clash() to resolve race condition on
conntrack insertions.

This is particularly a problem for connection-less protocols such as
UDP, with no initial handshake. Two or more packets may race to insert
the entry resulting in packet drops.

Another problematic scenario are packets enqueued to userspace via
NFQUEUE after the raw table, that make it easier to trigger this
race.

To resolve this, the idea is to reset the conntrack entry to the one
that won race. Packet and bytes counters are also merged.

The 'insert_failed' stats still accounts for this situation, after
this patch, the drop counter is bumped whenever we drop packets, so we
can watch for unresolved clashes.

Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
---
 include/net/netfilter/nf_conntrack_l4proto.h |  3 ++
 net/netfilter/nf_conntrack_core.c            | 45 +++++++++++++++++++++++++++-
 net/netfilter/nf_conntrack_proto_udp.c       |  2 ++
 net/netfilter/nf_conntrack_proto_udplite.c   |  2 ++
 4 files changed, 51 insertions(+), 1 deletion(-)

diff --git a/include/net/netfilter/nf_conntrack_l4proto.h b/include/net/netfilter/nf_conntrack_l4proto.h
index 956d8a6..1a5fb36 100644
--- a/include/net/netfilter/nf_conntrack_l4proto.h
+++ b/include/net/netfilter/nf_conntrack_l4proto.h
@@ -23,6 +23,9 @@ struct nf_conntrack_l4proto {
 	/* L4 Protocol number. */
 	u_int8_t l4proto;
 
+	/* Resolve clashes on insertion races. */
+	bool allow_clash;
+
 	/* Try to fill in the third arg: dataoff is offset past network protocol
            hdr.  Return true if possible. */
 	bool (*pkt_to_tuple)(const struct sk_buff *skb, unsigned int dataoff,
diff --git a/net/netfilter/nf_conntrack_core.c b/net/netfilter/nf_conntrack_core.c
index 8462b54..126e6f5 100644
--- a/net/netfilter/nf_conntrack_core.c
+++ b/net/netfilter/nf_conntrack_core.c
@@ -616,6 +616,47 @@ static inline void nf_ct_acct_update(struct nf_conn *ct,
 	}
 }
 
+static void nf_ct_acct_merge(struct nf_conn *ct, enum ip_conntrack_info ctinfo,
+			     const struct nf_conn *old_ct)
+{
+	struct nf_conn_acct *acct;
+
+	acct = nf_conn_acct_find(old_ct);
+	if (acct) {
+		struct nf_conn_counter *counter = acct->counter;
+		enum ip_conntrack_info ctinfo;
+		unsigned int bytes;
+
+		/* u32 should be fine since we must have seen one packet. */
+		bytes = atomic64_read(&counter[CTINFO2DIR(ctinfo)].bytes);
+		nf_ct_acct_update(ct, ctinfo, bytes);
+	}
+}
+
+/* Resolve race on insertion if this protocol allows this. */
+static int nf_ct_resolve_clash(struct net *net, struct sk_buff *skb,
+			       const struct nf_conn *old_ct,
+			       enum ip_conntrack_info ctinfo,
+			       struct nf_conntrack_tuple_hash *h)
+{
+	struct nf_conn *ct = nf_ct_tuplehash_to_ctrack(h);
+	struct nf_conntrack_l4proto *l4proto;
+
+	l4proto = __nf_ct_l4proto_find(nf_ct_l3num(ct), nf_ct_protonum(ct));
+	if (l4proto->allow_clash &&
+	    !nf_ct_is_dying(ct) &&
+	    atomic_inc_not_zero(&ct->ct_general.use)) {
+		/* Don't modify skb->nfctinfo, we're at POSTROUTING so this
+		 * packet is already leaving our framework, it is too late.
+		 */
+		skb->nfct = &ct->ct_general;
+		nf_ct_acct_merge(ct, ctinfo, old_ct);
+		return NF_ACCEPT;
+	}
+	NF_CT_STAT_INC(net, drop);
+	return NF_DROP;
+}
+
 /* Confirm a connection given skb; places it in hash table */
 int
 __nf_conntrack_confirm(struct sk_buff *skb)
@@ -630,6 +671,7 @@ __nf_conntrack_confirm(struct sk_buff *skb)
 	enum ip_conntrack_info ctinfo;
 	struct net *net;
 	unsigned int sequence;
+	int ret;
 
 	ct = nf_ct_get(skb, &ctinfo);
 	net = nf_ct_net(ct);
@@ -726,11 +768,12 @@ __nf_conntrack_confirm(struct sk_buff *skb)
 	return NF_ACCEPT;
 
 out:
+	ret = nf_ct_resolve_clash(net, skb, ct, ctinfo, h);
 	nf_ct_add_to_dying_list(ct);
 	nf_conntrack_double_unlock(hash, reply_hash);
 	NF_CT_STAT_INC(net, insert_failed);
 	local_bh_enable();
-	return NF_DROP;
+	return ret;
 }
 EXPORT_SYMBOL_GPL(__nf_conntrack_confirm);
 
diff --git a/net/netfilter/nf_conntrack_proto_udp.c b/net/netfilter/nf_conntrack_proto_udp.c
index 478f92f..4fd0405 100644
--- a/net/netfilter/nf_conntrack_proto_udp.c
+++ b/net/netfilter/nf_conntrack_proto_udp.c
@@ -309,6 +309,7 @@ struct nf_conntrack_l4proto nf_conntrack_l4proto_udp4 __read_mostly =
 	.l3proto		= PF_INET,
 	.l4proto		= IPPROTO_UDP,
 	.name			= "udp",
+	.allow_clash		= true,
 	.pkt_to_tuple		= udp_pkt_to_tuple,
 	.invert_tuple		= udp_invert_tuple,
 	.print_tuple		= udp_print_tuple,
@@ -341,6 +342,7 @@ struct nf_conntrack_l4proto nf_conntrack_l4proto_udp6 __read_mostly =
 	.l3proto		= PF_INET6,
 	.l4proto		= IPPROTO_UDP,
 	.name			= "udp",
+	.allow_clash		= true,
 	.pkt_to_tuple		= udp_pkt_to_tuple,
 	.invert_tuple		= udp_invert_tuple,
 	.print_tuple		= udp_print_tuple,
diff --git a/net/netfilter/nf_conntrack_proto_udplite.c b/net/netfilter/nf_conntrack_proto_udplite.c
index 1ac8ee1..9d692f5 100644
--- a/net/netfilter/nf_conntrack_proto_udplite.c
+++ b/net/netfilter/nf_conntrack_proto_udplite.c
@@ -274,6 +274,7 @@ static struct nf_conntrack_l4proto nf_conntrack_l4proto_udplite4 __read_mostly =
 	.l3proto		= PF_INET,
 	.l4proto		= IPPROTO_UDPLITE,
 	.name			= "udplite",
+	.allow_clash		= true,
 	.pkt_to_tuple		= udplite_pkt_to_tuple,
 	.invert_tuple		= udplite_invert_tuple,
 	.print_tuple		= udplite_print_tuple,
@@ -306,6 +307,7 @@ static struct nf_conntrack_l4proto nf_conntrack_l4proto_udplite6 __read_mostly =
 	.l3proto		= PF_INET6,
 	.l4proto		= IPPROTO_UDPLITE,
 	.name			= "udplite",
+	.allow_clash		= true,
 	.pkt_to_tuple		= udplite_pkt_to_tuple,
 	.invert_tuple		= udplite_invert_tuple,
 	.print_tuple		= udplite_print_tuple,
-- 
2.1.4