diff options
Diffstat (limited to 'pkg/tcpip/stack/conntrack.go')
| -rw-r--r-- | pkg/tcpip/stack/conntrack.go | 631 |
1 files changed, 631 insertions, 0 deletions
diff --git a/pkg/tcpip/stack/conntrack.go b/pkg/tcpip/stack/conntrack.go new file mode 100644 index 000000000..7dd344b4f --- /dev/null +++ b/pkg/tcpip/stack/conntrack.go @@ -0,0 +1,631 @@ +// 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 stack + +import ( + "encoding/binary" + "sync" + "time" + + "gvisor.dev/gvisor/pkg/tcpip" + "gvisor.dev/gvisor/pkg/tcpip/hash/jenkins" + "gvisor.dev/gvisor/pkg/tcpip/header" + "gvisor.dev/gvisor/pkg/tcpip/transport/tcpconntrack" +) + +// Connection tracking is used to track and manipulate packets for NAT rules. +// The connection is created for a packet if it does not exist. Every +// connection contains two tuples (original and reply). The tuples are +// manipulated if there is a matching NAT rule. The packet is modified by +// looking at the tuples in the Prerouting and Output hooks. +// +// Currently, only TCP tracking is supported. + +// Our hash table has 16K buckets. +// TODO(gvisor.dev/issue/170): These should be tunable. +const numBuckets = 1 << 14 + +// Direction of the tuple. +type direction int + +const ( + dirOriginal direction = iota + dirReply +) + +// Manipulation type for the connection. +type manipType int + +const ( + manipNone manipType = iota + manipDstPrerouting + manipDstOutput +) + +// tuple holds a connection's identifying and manipulating data in one +// direction. It is immutable. +// +// +stateify savable +type tuple struct { + // tupleEntry is used to build an intrusive list of tuples. + tupleEntry + + tupleID + + // conn is the connection tracking entry this tuple belongs to. + conn *conn + + // direction is the direction of the tuple. + direction direction +} + +// tupleID uniquely identifies a connection in one direction. It currently +// contains enough information to distinguish between any TCP or UDP +// connection, and will need to be extended to support other protocols. +// +// +stateify savable +type tupleID struct { + srcAddr tcpip.Address + srcPort uint16 + dstAddr tcpip.Address + dstPort uint16 + transProto tcpip.TransportProtocolNumber + netProto tcpip.NetworkProtocolNumber +} + +// reply creates the reply tupleID. +func (ti tupleID) reply() tupleID { + return tupleID{ + srcAddr: ti.dstAddr, + srcPort: ti.dstPort, + dstAddr: ti.srcAddr, + dstPort: ti.srcPort, + transProto: ti.transProto, + netProto: ti.netProto, + } +} + +// conn is a tracked connection. +// +// +stateify savable +type conn struct { + // original is the tuple in original direction. It is immutable. + original tuple + + // reply is the tuple in reply direction. It is immutable. + reply tuple + + // manip indicates if the packet should be manipulated. It is immutable. + manip manipType + + // tcbHook indicates if the packet is inbound or outbound to + // update the state of tcb. It is immutable. + tcbHook Hook + + // mu protects all mutable state. + mu sync.Mutex `state:"nosave"` + // tcb is TCB control block. It is used to keep track of states + // of tcp connection and is protected by mu. + tcb tcpconntrack.TCB + // lastUsed is the last time the connection saw a relevant packet, and + // is updated by each packet on the connection. It is protected by mu. + lastUsed time.Time `state:".(unixTime)"` +} + +// timedOut returns whether the connection timed out based on its state. +func (cn *conn) timedOut(now time.Time) bool { + const establishedTimeout = 5 * 24 * time.Hour + const defaultTimeout = 120 * time.Second + cn.mu.Lock() + defer cn.mu.Unlock() + if cn.tcb.State() == tcpconntrack.ResultAlive { + // Use the same default as Linux, which doesn't delete + // established connections for 5(!) days. + return now.Sub(cn.lastUsed) > establishedTimeout + } + // Use the same default as Linux, which lets connections in most states + // other than established remain for <= 120 seconds. + return now.Sub(cn.lastUsed) > defaultTimeout +} + +// update the connection tracking state. +// +// Precondition: ct.mu must be held. +func (ct *conn) updateLocked(tcpHeader header.TCP, hook Hook) { + // Update the state of tcb. tcb assumes it's always initialized on the + // client. However, we only need to know whether the connection is + // established or not, so the client/server distinction isn't important. + // TODO(gvisor.dev/issue/170): Add support in tcpconntrack to handle + // other tcp states. + if ct.tcb.IsEmpty() { + ct.tcb.Init(tcpHeader) + } else if hook == ct.tcbHook { + ct.tcb.UpdateStateOutbound(tcpHeader) + } else { + ct.tcb.UpdateStateInbound(tcpHeader) + } +} + +// ConnTrack tracks all connections created for NAT rules. Most users are +// expected to only call handlePacket, insertRedirectConn, and maybeInsertNoop. +// +// ConnTrack keeps all connections in a slice of buckets, each of which holds a +// linked list of tuples. This gives us some desirable properties: +// - Each bucket has its own lock, lessening lock contention. +// - The slice is large enough that lists stay short (<10 elements on average). +// Thus traversal is fast. +// - During linked list traversal we reap expired connections. This amortizes +// the cost of reaping them and makes reapUnused faster. +// +// Locks are ordered by their location in the buckets slice. That is, a +// goroutine that locks buckets[i] can only lock buckets[j] s.t. i < j. +// +// +stateify savable +type ConnTrack struct { + // seed is a one-time random value initialized at stack startup + // and is used in the calculation of hash keys for the list of buckets. + // It is immutable. + seed uint32 + + // mu protects the buckets slice, but not buckets' contents. Only take + // the write lock if you are modifying the slice or saving for S/R. + mu sync.RWMutex `state:"nosave"` + + // buckets is protected by mu. + buckets []bucket +} + +// +stateify savable +type bucket struct { + // mu protects tuples. + mu sync.Mutex `state:"nosave"` + tuples tupleList +} + +// packetToTupleID converts packet to a tuple ID. It fails when pkt lacks a valid +// TCP header. +func packetToTupleID(pkt *PacketBuffer) (tupleID, *tcpip.Error) { + // TODO(gvisor.dev/issue/170): Need to support for other + // protocols as well. + netHeader := header.IPv4(pkt.NetworkHeader().View()) + if len(netHeader) < header.IPv4MinimumSize || netHeader.TransportProtocol() != header.TCPProtocolNumber { + return tupleID{}, tcpip.ErrUnknownProtocol + } + tcpHeader := header.TCP(pkt.TransportHeader().View()) + if len(tcpHeader) < header.TCPMinimumSize { + return tupleID{}, tcpip.ErrUnknownProtocol + } + + return tupleID{ + srcAddr: netHeader.SourceAddress(), + srcPort: tcpHeader.SourcePort(), + dstAddr: netHeader.DestinationAddress(), + dstPort: tcpHeader.DestinationPort(), + transProto: netHeader.TransportProtocol(), + netProto: header.IPv4ProtocolNumber, + }, nil +} + +// newConn creates new connection. +func newConn(orig, reply tupleID, manip manipType, hook Hook) *conn { + conn := conn{ + manip: manip, + tcbHook: hook, + lastUsed: time.Now(), + } + conn.original = tuple{conn: &conn, tupleID: orig} + conn.reply = tuple{conn: &conn, tupleID: reply, direction: dirReply} + return &conn +} + +// connFor gets the conn for pkt if it exists, or returns nil +// if it does not. It returns an error when pkt does not contain a valid TCP +// header. +// TODO(gvisor.dev/issue/170): Only TCP packets are supported. Need to support +// other transport protocols. +func (ct *ConnTrack) connFor(pkt *PacketBuffer) (*conn, direction) { + tid, err := packetToTupleID(pkt) + if err != nil { + return nil, dirOriginal + } + return ct.connForTID(tid) +} + +func (ct *ConnTrack) connForTID(tid tupleID) (*conn, direction) { + bucket := ct.bucket(tid) + now := time.Now() + + ct.mu.RLock() + defer ct.mu.RUnlock() + ct.buckets[bucket].mu.Lock() + defer ct.buckets[bucket].mu.Unlock() + + // Iterate over the tuples in a bucket, cleaning up any unused + // connections we find. + for other := ct.buckets[bucket].tuples.Front(); other != nil; other = other.Next() { + // Clean up any timed-out connections we happen to find. + if ct.reapTupleLocked(other, bucket, now) { + // The tuple expired. + continue + } + if tid == other.tupleID { + return other.conn, other.direction + } + } + + return nil, dirOriginal +} + +func (ct *ConnTrack) insertRedirectConn(pkt *PacketBuffer, hook Hook, rt RedirectTarget) *conn { + tid, err := packetToTupleID(pkt) + if err != nil { + return nil + } + if hook != Prerouting && hook != Output { + return nil + } + + // Create a new connection and change the port as per the iptables + // rule. This tuple will be used to manipulate the packet in + // handlePacket. + replyTID := tid.reply() + replyTID.srcAddr = rt.MinIP + replyTID.srcPort = rt.MinPort + var manip manipType + switch hook { + case Prerouting: + manip = manipDstPrerouting + case Output: + manip = manipDstOutput + } + conn := newConn(tid, replyTID, manip, hook) + ct.insertConn(conn) + return conn +} + +// insertConn inserts conn into the appropriate table bucket. +func (ct *ConnTrack) insertConn(conn *conn) { + // Lock the buckets in the correct order. + tupleBucket := ct.bucket(conn.original.tupleID) + replyBucket := ct.bucket(conn.reply.tupleID) + ct.mu.RLock() + defer ct.mu.RUnlock() + if tupleBucket < replyBucket { + ct.buckets[tupleBucket].mu.Lock() + ct.buckets[replyBucket].mu.Lock() + } else if tupleBucket > replyBucket { + ct.buckets[replyBucket].mu.Lock() + ct.buckets[tupleBucket].mu.Lock() + } else { + // Both tuples are in the same bucket. + ct.buckets[tupleBucket].mu.Lock() + } + + // Now that we hold the locks, ensure the tuple hasn't been inserted by + // another thread. + alreadyInserted := false + for other := ct.buckets[tupleBucket].tuples.Front(); other != nil; other = other.Next() { + if other.tupleID == conn.original.tupleID { + alreadyInserted = true + break + } + } + + if !alreadyInserted { + // Add the tuple to the map. + ct.buckets[tupleBucket].tuples.PushFront(&conn.original) + ct.buckets[replyBucket].tuples.PushFront(&conn.reply) + } + + // Unlocking can happen in any order. + ct.buckets[tupleBucket].mu.Unlock() + if tupleBucket != replyBucket { + ct.buckets[replyBucket].mu.Unlock() + } +} + +// handlePacketPrerouting manipulates ports for packets in Prerouting hook. +// TODO(gvisor.dev/issue/170): Change address for Prerouting hook. +func handlePacketPrerouting(pkt *PacketBuffer, conn *conn, dir direction) { + // If this is a noop entry, don't do anything. + if conn.manip == manipNone { + return + } + + netHeader := header.IPv4(pkt.NetworkHeader().View()) + tcpHeader := header.TCP(pkt.TransportHeader().View()) + + // For prerouting redirection, packets going in the original direction + // have their destinations modified and replies have their sources + // modified. + switch dir { + case dirOriginal: + port := conn.reply.srcPort + tcpHeader.SetDestinationPort(port) + netHeader.SetDestinationAddress(conn.reply.srcAddr) + case dirReply: + port := conn.original.dstPort + tcpHeader.SetSourcePort(port) + netHeader.SetSourceAddress(conn.original.dstAddr) + } + + // TODO(gvisor.dev/issue/170): TCP checksums aren't usually validated + // on inbound packets, so we don't recalculate them. However, we should + // support cases when they are validated, e.g. when we can't offload + // receive checksumming. + + netHeader.SetChecksum(0) + netHeader.SetChecksum(^netHeader.CalculateChecksum()) +} + +// handlePacketOutput manipulates ports for packets in Output hook. +func handlePacketOutput(pkt *PacketBuffer, conn *conn, gso *GSO, r *Route, dir direction) { + // If this is a noop entry, don't do anything. + if conn.manip == manipNone { + return + } + + netHeader := header.IPv4(pkt.NetworkHeader().View()) + tcpHeader := header.TCP(pkt.TransportHeader().View()) + + // For output redirection, packets going in the original direction + // have their destinations modified and replies have their sources + // modified. For prerouting redirection, we only reach this point + // when replying, so packet sources are modified. + if conn.manip == manipDstOutput && dir == dirOriginal { + port := conn.reply.srcPort + tcpHeader.SetDestinationPort(port) + netHeader.SetDestinationAddress(conn.reply.srcAddr) + } else { + port := conn.original.dstPort + tcpHeader.SetSourcePort(port) + netHeader.SetSourceAddress(conn.original.dstAddr) + } + + // Calculate the TCP checksum and set it. + tcpHeader.SetChecksum(0) + length := uint16(pkt.Size()) - uint16(netHeader.HeaderLength()) + xsum := r.PseudoHeaderChecksum(header.TCPProtocolNumber, length) + if gso != nil && gso.NeedsCsum { + tcpHeader.SetChecksum(xsum) + } else if r.Capabilities()&CapabilityTXChecksumOffload == 0 { + xsum = header.ChecksumVVWithOffset(pkt.Data, xsum, int(tcpHeader.DataOffset()), pkt.Data.Size()) + tcpHeader.SetChecksum(^tcpHeader.CalculateChecksum(xsum)) + } + + netHeader.SetChecksum(0) + netHeader.SetChecksum(^netHeader.CalculateChecksum()) +} + +// handlePacket will manipulate the port and address of the packet if the +// connection exists. Returns whether, after the packet traverses the tables, +// it should create a new entry in the table. +func (ct *ConnTrack) handlePacket(pkt *PacketBuffer, hook Hook, gso *GSO, r *Route) bool { + if pkt.NatDone { + return false + } + + if hook != Prerouting && hook != Output { + return false + } + + // TODO(gvisor.dev/issue/170): Support other transport protocols. + if nh := pkt.NetworkHeader().View(); nh.IsEmpty() || header.IPv4(nh).TransportProtocol() != header.TCPProtocolNumber { + return false + } + + conn, dir := ct.connFor(pkt) + // Connection or Rule not found for the packet. + if conn == nil { + return true + } + + tcpHeader := header.TCP(pkt.TransportHeader().View()) + if len(tcpHeader) < header.TCPMinimumSize { + return false + } + + switch hook { + case Prerouting: + handlePacketPrerouting(pkt, conn, dir) + case Output: + handlePacketOutput(pkt, conn, gso, r, dir) + } + pkt.NatDone = true + + // Update the state of tcb. + // TODO(gvisor.dev/issue/170): Add support in tcpcontrack to handle + // other tcp states. + conn.mu.Lock() + defer conn.mu.Unlock() + + // Mark the connection as having been used recently so it isn't reaped. + conn.lastUsed = time.Now() + // Update connection state. + conn.updateLocked(header.TCP(pkt.TransportHeader().View()), hook) + + return false +} + +// maybeInsertNoop tries to insert a no-op connection entry to keep connections +// from getting clobbered when replies arrive. It only inserts if there isn't +// already a connection for pkt. +// +// This should be called after traversing iptables rules only, to ensure that +// pkt.NatDone is set correctly. +func (ct *ConnTrack) maybeInsertNoop(pkt *PacketBuffer, hook Hook) { + // If there were a rule applying to this packet, it would be marked + // with NatDone. + if pkt.NatDone { + return + } + + // We only track TCP connections. + if nh := pkt.NetworkHeader().View(); nh.IsEmpty() || header.IPv4(nh).TransportProtocol() != header.TCPProtocolNumber { + return + } + + // This is the first packet we're seeing for the TCP connection. Insert + // the noop entry (an identity mapping) so that the response doesn't + // get NATed, breaking the connection. + tid, err := packetToTupleID(pkt) + if err != nil { + return + } + conn := newConn(tid, tid.reply(), manipNone, hook) + conn.updateLocked(header.TCP(pkt.TransportHeader().View()), hook) + ct.insertConn(conn) +} + +// bucket gets the conntrack bucket for a tupleID. +func (ct *ConnTrack) bucket(id tupleID) int { + h := jenkins.Sum32(ct.seed) + h.Write([]byte(id.srcAddr)) + h.Write([]byte(id.dstAddr)) + shortBuf := make([]byte, 2) + binary.LittleEndian.PutUint16(shortBuf, id.srcPort) + h.Write([]byte(shortBuf)) + binary.LittleEndian.PutUint16(shortBuf, id.dstPort) + h.Write([]byte(shortBuf)) + binary.LittleEndian.PutUint16(shortBuf, uint16(id.transProto)) + h.Write([]byte(shortBuf)) + binary.LittleEndian.PutUint16(shortBuf, uint16(id.netProto)) + h.Write([]byte(shortBuf)) + ct.mu.RLock() + defer ct.mu.RUnlock() + return int(h.Sum32()) % len(ct.buckets) +} + +// reapUnused deletes timed out entries from the conntrack map. The rules for +// reaping are: +// - Most reaping occurs in connFor, which is called on each packet. connFor +// cleans up the bucket the packet's connection maps to. Thus calls to +// reapUnused should be fast. +// - Each call to reapUnused traverses a fraction of the conntrack table. +// Specifically, it traverses len(ct.buckets)/fractionPerReaping. +// - After reaping, reapUnused decides when it should next run based on the +// ratio of expired connections to examined connections. If the ratio is +// greater than maxExpiredPct, it schedules the next run quickly. Otherwise it +// slightly increases the interval between runs. +// - maxFullTraversal caps the time it takes to traverse the entire table. +// +// reapUnused returns the next bucket that should be checked and the time after +// which it should be called again. +func (ct *ConnTrack) reapUnused(start int, prevInterval time.Duration) (int, time.Duration) { + // TODO(gvisor.dev/issue/170): This can be more finely controlled, as + // it is in Linux via sysctl. + const fractionPerReaping = 128 + const maxExpiredPct = 50 + const maxFullTraversal = 60 * time.Second + const minInterval = 10 * time.Millisecond + const maxInterval = maxFullTraversal / fractionPerReaping + + now := time.Now() + checked := 0 + expired := 0 + var idx int + ct.mu.RLock() + defer ct.mu.RUnlock() + for i := 0; i < len(ct.buckets)/fractionPerReaping; i++ { + idx = (i + start) % len(ct.buckets) + ct.buckets[idx].mu.Lock() + for tuple := ct.buckets[idx].tuples.Front(); tuple != nil; tuple = tuple.Next() { + checked++ + if ct.reapTupleLocked(tuple, idx, now) { + expired++ + } + } + ct.buckets[idx].mu.Unlock() + } + // We already checked buckets[idx]. + idx++ + + // If half or more of the connections are expired, the table has gotten + // stale. Reschedule quickly. + expiredPct := 0 + if checked != 0 { + expiredPct = expired * 100 / checked + } + if expiredPct > maxExpiredPct { + return idx, minInterval + } + if interval := prevInterval + minInterval; interval <= maxInterval { + // Increment the interval between runs. + return idx, interval + } + // We've hit the maximum interval. + return idx, maxInterval +} + +// reapTupleLocked tries to remove tuple and its reply from the table. It +// returns whether the tuple's connection has timed out. +// +// Preconditions: ct.mu is locked for reading and bucket is locked. +func (ct *ConnTrack) reapTupleLocked(tuple *tuple, bucket int, now time.Time) bool { + if !tuple.conn.timedOut(now) { + return false + } + + // To maintain lock order, we can only reap these tuples if the reply + // appears later in the table. + replyBucket := ct.bucket(tuple.reply()) + if bucket > replyBucket { + return true + } + + // Don't re-lock if both tuples are in the same bucket. + differentBuckets := bucket != replyBucket + if differentBuckets { + ct.buckets[replyBucket].mu.Lock() + } + + // We have the buckets locked and can remove both tuples. + if tuple.direction == dirOriginal { + ct.buckets[replyBucket].tuples.Remove(&tuple.conn.reply) + } else { + ct.buckets[replyBucket].tuples.Remove(&tuple.conn.original) + } + ct.buckets[bucket].tuples.Remove(tuple) + + // Don't re-unlock if both tuples are in the same bucket. + if differentBuckets { + ct.buckets[replyBucket].mu.Unlock() + } + + return true +} + +func (ct *ConnTrack) originalDst(epID TransportEndpointID) (tcpip.Address, uint16, *tcpip.Error) { + // Lookup the connection. The reply's original destination + // describes the original address. + tid := tupleID{ + srcAddr: epID.LocalAddress, + srcPort: epID.LocalPort, + dstAddr: epID.RemoteAddress, + dstPort: epID.RemotePort, + transProto: header.TCPProtocolNumber, + netProto: header.IPv4ProtocolNumber, + } + conn, _ := ct.connForTID(tid) + if conn == nil { + // Not a tracked connection. + return "", 0, tcpip.ErrNotConnected + } else if conn.manip == manipNone { + // Unmanipulated connection. + return "", 0, tcpip.ErrInvalidOptionValue + } + + return conn.original.dstAddr, conn.original.dstPort, nil +} |