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// Copyright 2020 The gVisor Authors.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
package iptables
import (
"fmt"
"gvisor.dev/gvisor/pkg/log"
"gvisor.dev/gvisor/pkg/tcpip"
"gvisor.dev/gvisor/pkg/tcpip/header"
)
type TCPMatcher struct {
data TCPMatcherData
// tablename string
// unsigned int matchsize;
// unsigned int usersize;
// #ifdef CONFIG_COMPAT
// unsigned int compatsize;
// #endif
// unsigned int hooks;
// unsigned short proto;
// unsigned short family;
}
// TODO: Delete?
// MatchCheckEntryParams
type TCPMatcherData struct {
// Filter IPHeaderFilter
SourcePortStart uint16
SourcePortEnd uint16
DestinationPortStart uint16
DestinationPortEnd uint16
Option uint8
FlagMask uint8
FlagCompare uint8
InverseFlags uint8
}
func NewTCPMatcher(filter IPHeaderFilter, data TCPMatcherData) (Matcher, error) {
// TODO: We currently only support source port and destination port.
log.Infof("Adding rule with TCPMatcherData: %+v", data)
if data.Option != 0 ||
data.FlagMask != 0 ||
data.FlagCompare != 0 ||
data.InverseFlags != 0 {
return nil, fmt.Errorf("unsupported TCP matcher flags set")
}
if filter.Protocol != header.TCPProtocolNumber {
log.Warningf("TCP matching is only valid for protocol %d.", header.TCPProtocolNumber)
}
return &TCPMatcher{data: data}, nil
}
// TODO: Check xt_tcpudp.c. Need to check for same things (e.g. fragments).
func (tm *TCPMatcher) Match(hook Hook, pkt tcpip.PacketBuffer, interfaceName string) (bool, bool) {
netHeader := header.IPv4(pkt.NetworkHeader)
// TODO: Do we check proto here or elsewhere? I think elsewhere (check
// codesearch).
if netHeader.TransportProtocol() != header.TCPProtocolNumber {
return false, false
}
// We dont't match fragments.
if frag := netHeader.FragmentOffset(); frag != 0 {
if frag == 1 {
log.Warningf("Dropping TCP packet: malicious packet with fragment with fragment offest of 1.")
return false, true
}
return false, false
}
// Now we need the transport header. However, this may not have been set
// yet.
// TODO
var tcpHeader header.TCP
if pkt.TransportHeader != nil {
tcpHeader = header.TCP(pkt.TransportHeader)
} else {
// The TCP header hasn't been parsed yet. We have to do it here.
if len(pkt.Data.First()) < header.TCPMinimumSize {
// There's no valid TCP header here, so we hotdrop the
// packet.
// TODO: Stats.
log.Warningf("Dropping TCP packet: size to small.")
return false, true
}
tcpHeader = header.TCP(pkt.Data.First())
}
// Check whether the source and destination ports are within the
// matching range.
sourcePort := tcpHeader.SourcePort()
destinationPort := tcpHeader.DestinationPort()
if sourcePort < tm.data.SourcePortStart || tm.data.SourcePortEnd < sourcePort {
return false, false
}
if destinationPort < tm.data.DestinationPortStart || tm.data.DestinationPortEnd < destinationPort {
return false, false
}
return true, false
}
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