Fix bridge connection reset due to invalid packets

Add drop of conntrack INVALID packets in input
such that invalid packets due to TCP window overflow do
not cause a connection reset.

Due to some netfilter/conntrack limitations, invalid packets
are never treated as NAT'ed but reassigned to the
host and considered martians.
This causes a RST response from the host and resets the connection.
As soon as NAT is setup, for bridge networks for instance,
invalid packets have to be dropped in input.

The implementation adds a generic DOCKER-INPUT chain prefilled
with a rule for dropping invalid packets and a return rule.
As soon as some bridge network is setup, the DOCKER-INPUT
chain call is inserted in the filter table INPUT chain.

Fixes moby#1090.

Signed-off-by: Christophe Guillon <christophe.guillon@st.com>

drivers/bridge/setup_ip_tables.go

@@ -12,7 +12,8 @@ import (
 
 // DockerChain: DOCKER iptable chain name
 const (
-	DockerChain = "DOCKER"
+	DockerChain      = "DOCKER"
+	DockerInputChain = "DOCKER-INPUT"
 	// Isolation between bridge networks is achieved in two stages by means
 	// of the following two chains in the filter table. The first chain matches
 	// on the source interface being a bridge network's bridge and the
@@ -58,6 +59,18 @@ func setupIPChains(config *configuration) (*iptables.ChainInfo, *iptables.ChainI
 		}
 	}()
 
+	_, err = iptables.NewChain(DockerInputChain, iptables.Filter, false)
+	if err != nil {
+		return nil, nil, nil, nil, fmt.Errorf("failed to create INPUT chain %s: %v", DockerInputChain, err)
+	}
+	defer func() {
+		if err != nil {
+			if err := iptables.RemoveExistingChain(DockerInputChain, iptables.Filter); err != nil {
+				logrus.Warnf("failed on removing iptables INPUT chain %s on cleanup: %v", DockerInputChain, err)
+			}
+		}
+	}()
+
 	isolationChain1, err := iptables.NewChain(IsolationChain1, iptables.Filter, false)
 	if err != nil {
 		return nil, nil, nil, nil, fmt.Errorf("failed to create FILTER isolation chain: %v", err)
@@ -82,6 +95,10 @@ func setupIPChains(config *configuration) (*iptables.ChainInfo, *iptables.ChainI
 		}
 	}()
 
+	if err := iptables.AddReturnRule(DockerInputChain); err != nil {
+		return nil, nil, nil, nil, err
+	}
+
 	if err := iptables.AddReturnRule(IsolationChain1); err != nil {
 		return nil, nil, nil, nil, err
 	}
@@ -90,6 +107,10 @@ func setupIPChains(config *configuration) (*iptables.ChainInfo, *iptables.ChainI
 		return nil, nil, nil, nil, err
 	}
 
+	if err := iptables.ProgramRule(iptables.Filter, DockerInputChain, iptables.Insert, []string{"-m", "conntrack", "--ctstate", "INVALID", "-j", "DROP"}); err != nil {
+		return nil, nil, nil, nil, err
+	}
+
 	return natChain, filterChain, isolationChain1, isolationChain2, nil
 }
 
@@ -149,6 +170,13 @@ func (n *bridgeNetwork) setupIPTables(config *networkConfiguration, i *bridgeInt
 		n.portMapper.SetIptablesChain(natChain, n.getNetworkBridgeName())
 	}
 
+	d.Lock()
+	err = iptables.EnsureJumpRule("INPUT", DockerInputChain)
+	d.Unlock()
+	if err != nil {
+		return err
+	}
+
 	d.Lock()
 	err = iptables.EnsureJumpRule("FORWARD", IsolationChain1)
 	d.Unlock()
@@ -321,10 +349,14 @@ func removeIPChains() {
 	// Remove obsolete rules from default chains
 	iptables.ProgramRule(iptables.Filter, "FORWARD", iptables.Delete, []string{"-j", oldIsolationChain})
 
+	// Remove possibly installed references to chains
+	iptables.ProgramRule(iptables.Filter, "INPUT", iptables.Delete, []string{"-j", DockerInputChain})
+
 	// Remove chains
 	for _, chainInfo := range []iptables.ChainInfo{
 		{Name: DockerChain, Table: iptables.Nat},
 		{Name: DockerChain, Table: iptables.Filter},
+		{Name: DockerInputChain, Table: iptables.Filter},
 		{Name: IsolationChain1, Table: iptables.Filter},
 		{Name: IsolationChain2, Table: iptables.Filter},
 		{Name: oldIsolationChain, Table: iptables.Filter},