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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"
)
// TODO(gvisor.dev/issue/170): The following per-matcher params should be
// supported:
// - Table name
// - Match size
// - User size
// - Hooks
// - Proto
// - Family
// UDPMatcher matches UDP packets and their headers. It implements Matcher.
type UDPMatcher struct {
Data UDPMatcherParams
}
// UDPMatcherParams are the parameters used to create a UDPMatcher.
type UDPMatcherParams struct {
SourcePortStart uint16
SourcePortEnd uint16
DestinationPortStart uint16
DestinationPortEnd uint16
InverseFlags uint8
}
// NewUDPMatcher returns a new instance of UDPMatcher.
func NewUDPMatcher(filter IPHeaderFilter, data UDPMatcherParams) (Matcher, error) {
log.Infof("Adding rule with UDPMatcherParams: %+v", data)
if data.InverseFlags != 0 {
return nil, fmt.Errorf("unsupported UDP matcher inverse flags set")
}
if filter.Protocol != header.UDPProtocolNumber {
return nil, fmt.Errorf("UDP matching is only valid for protocol %d.", header.UDPProtocolNumber)
}
return &UDPMatcher{Data: data}, nil
}
// Match implements Matcher.Match.
func (um *UDPMatcher) Match(hook Hook, pkt tcpip.PacketBuffer, interfaceName string) (bool, bool) {
netHeader := header.IPv4(pkt.NetworkHeader)
// TODO(gvisor.dev/issue/170): Proto checks should ultimately be moved
// into the iptables.Check codepath as matchers are added.
if netHeader.TransportProtocol() != header.UDPProtocolNumber {
return false, false
}
// We dont't match fragments.
if frag := netHeader.FragmentOffset(); frag != 0 {
if frag == 1 {
return false, true
}
log.Warningf("Dropping UDP packet: malicious fragmented packet.")
return false, false
}
// Now we need the transport header. However, this may not have been set
// yet.
// TODO(gvisor.dev/issue/170): Parsing the transport header should
// ultimately be moved into the iptables.Check codepath as matchers are
// added.
var udpHeader header.UDP
if pkt.TransportHeader != nil {
udpHeader = header.UDP(pkt.TransportHeader)
} else {
// The UDP header hasn't been parsed yet. We have to do it here.
if len(pkt.Data.First()) < header.UDPMinimumSize {
// There's no valid UDP header here, so we hotdrop the
// packet.
log.Warningf("Dropping UDP packet: size too small.")
return false, true
}
udpHeader = header.UDP(pkt.Data.First())
}
// Check whether the source and destination ports are within the
// matching range.
sourcePort := udpHeader.SourcePort()
destinationPort := udpHeader.DestinationPort()
if sourcePort < um.Data.SourcePortStart || um.Data.SourcePortEnd < sourcePort {
return false, false
}
if destinationPort < um.Data.DestinationPortStart || um.Data.DestinationPortEnd < destinationPort {
return false, false
}
return true, false
}
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