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Diffstat (limited to 'pkg/tcpip/stack/ndp.go')
| -rw-r--r-- | pkg/tcpip/stack/ndp.go | 534 |
1 files changed, 534 insertions, 0 deletions
diff --git a/pkg/tcpip/stack/ndp.go b/pkg/tcpip/stack/ndp.go new file mode 100644 index 000000000..8e49f7a56 --- /dev/null +++ b/pkg/tcpip/stack/ndp.go @@ -0,0 +1,534 @@ +// Copyright 2019 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 ( + "fmt" + "log" + "time" + + "gvisor.dev/gvisor/pkg/tcpip" + "gvisor.dev/gvisor/pkg/tcpip/buffer" + "gvisor.dev/gvisor/pkg/tcpip/header" +) + +const ( + // defaultDupAddrDetectTransmits is the default number of NDP Neighbor + // Solicitation messages to send when doing Duplicate Address Detection + // for a tentative address. + // + // Default = 1 (from RFC 4862 section 5.1) + defaultDupAddrDetectTransmits = 1 + + // defaultRetransmitTimer is the default amount of time to wait between + // sending NDP Neighbor solicitation messages. + // + // Default = 1s (from RFC 4861 section 10). + defaultRetransmitTimer = time.Second + + // defaultHandleRAs is the default configuration for whether or not to + // handle incoming Router Advertisements as a host. + // + // Default = true. + defaultHandleRAs = true + + // defaultDiscoverDefaultRouters is the default configuration for + // whether or not to discover default routers from incoming Router + // Advertisements as a host. + // + // Default = true. + defaultDiscoverDefaultRouters = true + + // minimumRetransmitTimer is the minimum amount of time to wait between + // sending NDP Neighbor solicitation messages. Note, RFC 4861 does + // not impose a minimum Retransmit Timer, but we do here to make sure + // the messages are not sent all at once. We also come to this value + // because in the RetransmitTimer field of a Router Advertisement, a + // value of 0 means unspecified, so the smallest valid value is 1. + // Note, the unit of the RetransmitTimer field in the Router + // Advertisement is milliseconds. + // + // Min = 1ms. + minimumRetransmitTimer = time.Millisecond + + // MaxDiscoveredDefaultRouters is the maximum number of discovered + // default routers. The stack should stop discovering new routers after + // discovering MaxDiscoveredDefaultRouters routers. + // + // This value MUST be at minimum 2 as per RFC 4861 section 6.3.4, and + // SHOULD be more. + // + // Max = 10. + MaxDiscoveredDefaultRouters = 10 +) + +// NDPDispatcher is the interface integrators of netstack must implement to +// receive and handle NDP related events. +type NDPDispatcher interface { + // OnDuplicateAddressDetectionStatus will be called when the DAD process + // for an address (addr) on a NIC (with ID nicID) completes. resolved + // will be set to true if DAD completed successfully (no duplicate addr + // detected); false otherwise (addr was detected to be a duplicate on + // the link the NIC is a part of, or it was stopped for some other + // reason, such as the address being removed). If an error occured + // during DAD, err will be set and resolved must be ignored. + // + // This function is permitted to block indefinitely without interfering + // with the stack's operation. + OnDuplicateAddressDetectionStatus(nicID tcpip.NICID, addr tcpip.Address, resolved bool, err *tcpip.Error) + + // OnDefaultRouterDiscovered will be called when a new default router is + // discovered. Implementations must return true along with a new valid + // route table if the newly discovered router should be remembered. If + // an implementation returns false, the second return value will be + // ignored. + // + // This function is not permitted to block indefinitely. This function + // is also not permitted to call into the stack. + OnDefaultRouterDiscovered(nicID tcpip.NICID, addr tcpip.Address) (bool, []tcpip.Route) + + // OnDefaultRouterInvalidated will be called when a discovered default + // router is invalidated. Implementers must return a new valid route + // table. + // + // This function is not permitted to block indefinitely. This function + // is also not permitted to call into the stack. + OnDefaultRouterInvalidated(nicID tcpip.NICID, addr tcpip.Address) []tcpip.Route +} + +// NDPConfigurations is the NDP configurations for the netstack. +type NDPConfigurations struct { + // The number of Neighbor Solicitation messages to send when doing + // Duplicate Address Detection for a tentative address. + // + // Note, a value of zero effectively disables DAD. + DupAddrDetectTransmits uint8 + + // The amount of time to wait between sending Neighbor solicitation + // messages. + // + // Must be greater than 0.5s. + RetransmitTimer time.Duration + + // HandleRAs determines whether or not Router Advertisements will be + // processed. + HandleRAs bool + + // DiscoverDefaultRouters determines whether or not default routers will + // be discovered from Router Advertisements. This configuration is + // ignored if HandleRAs is false. + DiscoverDefaultRouters bool +} + +// DefaultNDPConfigurations returns an NDPConfigurations populated with +// default values. +func DefaultNDPConfigurations() NDPConfigurations { + return NDPConfigurations{ + DupAddrDetectTransmits: defaultDupAddrDetectTransmits, + RetransmitTimer: defaultRetransmitTimer, + HandleRAs: defaultHandleRAs, + DiscoverDefaultRouters: defaultDiscoverDefaultRouters, + } +} + +// validate modifies an NDPConfigurations with valid values. If invalid values +// are present in c, the corresponding default values will be used instead. +// +// If RetransmitTimer is less than minimumRetransmitTimer, then a value of +// defaultRetransmitTimer will be used. +func (c *NDPConfigurations) validate() { + if c.RetransmitTimer < minimumRetransmitTimer { + c.RetransmitTimer = defaultRetransmitTimer + } +} + +// ndpState is the per-interface NDP state. +type ndpState struct { + // The NIC this ndpState is for. + nic *NIC + + // configs is the per-interface NDP configurations. + configs NDPConfigurations + + // The DAD state to send the next NS message, or resolve the address. + dad map[tcpip.Address]dadState + + // The default routers discovered through Router Advertisements. + defaultRouters map[tcpip.Address]defaultRouterState +} + +// dadState holds the Duplicate Address Detection timer and channel to signal +// to the DAD goroutine that DAD should stop. +type dadState struct { + // The DAD timer to send the next NS message, or resolve the address. + timer *time.Timer + + // Used to let the DAD timer know that it has been stopped. + // + // Must only be read from or written to while protected by the lock of + // the NIC this dadState is associated with. + done *bool +} + +// defaultRouterState holds data associated with a default router discovered by +// a Router Advertisement. +type defaultRouterState struct { + invalidationTimer *time.Timer + + // Used to signal the timer not to invalidate the default router (R) in + // a race condition (T1 is a goroutine that handles an RA from R and T2 + // is the goroutine that handles R's invalidation timer firing): + // T1: Receive a new RA from R + // T1: Obtain the NIC's lock before processing the RA + // T2: R's invalidation timer fires, and gets blocked on obtaining the + // NIC's lock + // T1: Refreshes/extends R's lifetime & releases NIC's lock + // T2: Obtains NIC's lock & invalidates R immediately + // + // To resolve this, T1 will check to see if the timer already fired, and + // signal the timer using this channel to not invalidate R, so that once + // T2 obtains the lock, it will see that there is an event on this + // channel and do nothing further. + doNotInvalidateC chan struct{} +} + +// startDuplicateAddressDetection performs Duplicate Address Detection. +// +// This function must only be called by IPv6 addresses that are currently +// tentative. +// +// The NIC that ndp belongs to MUST be locked. +func (ndp *ndpState) startDuplicateAddressDetection(addr tcpip.Address, ref *referencedNetworkEndpoint) *tcpip.Error { + // addr must be a valid unicast IPv6 address. + if !header.IsV6UnicastAddress(addr) { + return tcpip.ErrAddressFamilyNotSupported + } + + // Should not attempt to perform DAD on an address that is currently in + // the DAD process. + if _, ok := ndp.dad[addr]; ok { + // Should never happen because we should only ever call this + // function for newly created addresses. If we attemped to + // "add" an address that already existed, we would returned an + // error since we attempted to add a duplicate address, or its + // reference count would have been increased without doing the + // work that would have been done for an address that was brand + // new. See NIC.addPermanentAddressLocked. + panic(fmt.Sprintf("ndpdad: already performing DAD for addr %s on NIC(%d)", addr, ndp.nic.ID())) + } + + remaining := ndp.configs.DupAddrDetectTransmits + + { + done, err := ndp.doDuplicateAddressDetection(addr, remaining, ref) + if err != nil { + return err + } + if done { + return nil + } + } + + remaining-- + + var done bool + var timer *time.Timer + timer = time.AfterFunc(ndp.configs.RetransmitTimer, func() { + var d bool + var err *tcpip.Error + + // doDadIteration does a single iteration of the DAD loop. + // + // Returns true if the integrator needs to be informed of DAD + // completing. + doDadIteration := func() bool { + ndp.nic.mu.Lock() + defer ndp.nic.mu.Unlock() + + if done { + // If we reach this point, it means that the DAD + // timer fired after another goroutine already + // obtained the NIC lock and stopped DAD before + // this function obtained the NIC lock. Simply + // return here and do nothing further. + return false + } + + ref, ok := ndp.nic.endpoints[NetworkEndpointID{addr}] + if !ok { + // This should never happen. + // We should have an endpoint for addr since we + // are still performing DAD on it. If the + // endpoint does not exist, but we are doing DAD + // on it, then we started DAD at some point, but + // forgot to stop it when the endpoint was + // deleted. + panic(fmt.Sprintf("ndpdad: unrecognized addr %s for NIC(%d)", addr, ndp.nic.ID())) + } + + d, err = ndp.doDuplicateAddressDetection(addr, remaining, ref) + if err != nil || d { + delete(ndp.dad, addr) + + if err != nil { + log.Printf("ndpdad: Error occured during DAD iteration for addr (%s) on NIC(%d); err = %s", addr, ndp.nic.ID(), err) + } + + // Let the integrator know DAD has completed. + return true + } + + remaining-- + timer.Reset(ndp.nic.stack.ndpConfigs.RetransmitTimer) + return false + } + + if doDadIteration() && ndp.nic.stack.ndpDisp != nil { + ndp.nic.stack.ndpDisp.OnDuplicateAddressDetectionStatus(ndp.nic.ID(), addr, d, err) + } + }) + + ndp.dad[addr] = dadState{ + timer: timer, + done: &done, + } + + return nil +} + +// doDuplicateAddressDetection is called on every iteration of the timer, and +// when DAD starts. +// +// It handles resolving the address (if there are no more NS to send), or +// sending the next NS if there are more NS to send. +// +// This function must only be called by IPv6 addresses that are currently +// tentative. +// +// The NIC that ndp belongs to (n) MUST be locked. +// +// Returns true if DAD has resolved; false if DAD is still ongoing. +func (ndp *ndpState) doDuplicateAddressDetection(addr tcpip.Address, remaining uint8, ref *referencedNetworkEndpoint) (bool, *tcpip.Error) { + if ref.getKind() != permanentTentative { + // The endpoint should still be marked as tentative + // since we are still performing DAD on it. + panic(fmt.Sprintf("ndpdad: addr %s is not tentative on NIC(%d)", addr, ndp.nic.ID())) + } + + if remaining == 0 { + // DAD has resolved. + ref.setKind(permanent) + return true, nil + } + + // Send a new NS. + snmc := header.SolicitedNodeAddr(addr) + snmcRef, ok := ndp.nic.endpoints[NetworkEndpointID{snmc}] + if !ok { + // This should never happen as if we have the + // address, we should have the solicited-node + // address. + panic(fmt.Sprintf("ndpdad: NIC(%d) is not in the solicited-node multicast group (%s) but it has addr %s", ndp.nic.ID(), snmc, addr)) + } + + // Use the unspecified address as the source address when performing + // DAD. + r := makeRoute(header.IPv6ProtocolNumber, header.IPv6Any, snmc, ndp.nic.linkEP.LinkAddress(), snmcRef, false, false) + + hdr := buffer.NewPrependable(int(r.MaxHeaderLength()) + header.ICMPv6NeighborSolicitMinimumSize) + pkt := header.ICMPv6(hdr.Prepend(header.ICMPv6NeighborSolicitMinimumSize)) + pkt.SetType(header.ICMPv6NeighborSolicit) + ns := header.NDPNeighborSolicit(pkt.NDPPayload()) + ns.SetTargetAddress(addr) + pkt.SetChecksum(header.ICMPv6Checksum(pkt, r.LocalAddress, r.RemoteAddress, buffer.VectorisedView{})) + + sent := r.Stats().ICMP.V6PacketsSent + if err := r.WritePacket(nil, hdr, buffer.VectorisedView{}, NetworkHeaderParams{Protocol: header.ICMPv6ProtocolNumber, TTL: header.NDPHopLimit, TOS: DefaultTOS}); err != nil { + sent.Dropped.Increment() + return false, err + } + sent.NeighborSolicit.Increment() + + return false, nil +} + +// stopDuplicateAddressDetection ends a running Duplicate Address Detection +// process. Note, this may leave the DAD process for a tentative address in +// such a state forever, unless some other external event resolves the DAD +// process (receiving an NA from the true owner of addr, or an NS for addr +// (implying another node is attempting to use addr)). It is up to the caller +// of this function to handle such a scenario. Normally, addr will be removed +// from n right after this function returns or the address successfully +// resolved. +// +// The NIC that ndp belongs to MUST be locked. +func (ndp *ndpState) stopDuplicateAddressDetection(addr tcpip.Address) { + dad, ok := ndp.dad[addr] + if !ok { + // Not currently performing DAD on addr, just return. + return + } + + if dad.timer != nil { + dad.timer.Stop() + dad.timer = nil + + *dad.done = true + dad.done = nil + } + + delete(ndp.dad, addr) + + // Let the integrator know DAD did not resolve. + if ndp.nic.stack.ndpDisp != nil { + go ndp.nic.stack.ndpDisp.OnDuplicateAddressDetectionStatus(ndp.nic.ID(), addr, false, nil) + } +} + +// handleRA handles a Router Advertisement message that arrived on the NIC +// this ndp is for. Does nothing if the NIC is configured to not handle RAs. +// +// The NIC that ndp belongs to and its associated stack MUST be locked. +func (ndp *ndpState) handleRA(ip tcpip.Address, ra header.NDPRouterAdvert) { + // Is the NIC configured to handle RAs at all? + // + // Currently, the stack does not determine router interface status on a + // per-interface basis; it is a stack-wide configuration, so we check + // stack's forwarding flag to determine if the NIC is a routing + // interface. + if !ndp.configs.HandleRAs || ndp.nic.stack.forwarding { + return + } + + // Is the NIC configured to discover default routers? + if ndp.configs.DiscoverDefaultRouters { + rtr, ok := ndp.defaultRouters[ip] + rl := ra.RouterLifetime() + switch { + case !ok && rl != 0: + // This is a new default router we are discovering. + // + // Only remember it if we currently know about less than + // MaxDiscoveredDefaultRouters routers. + if len(ndp.defaultRouters) < MaxDiscoveredDefaultRouters { + ndp.rememberDefaultRouter(ip, rl) + } + + case ok && rl != 0: + // This is an already discovered default router. Update + // the invalidation timer. + timer := rtr.invalidationTimer + + // We should ALWAYS have an invalidation timer for a + // discovered router. + if timer == nil { + panic("ndphandlera: RA invalidation timer should not be nil") + } + + if !timer.Stop() { + // If we reach this point, then we know the + // timer fired after we already took the NIC + // lock. Signal the timer so that once it + // obtains the lock, it doesn't actually + // invalidate the router as we just got a new + // RA that refreshes its lifetime to a non-zero + // value. See + // defaultRouterState.doNotInvalidateC for more + // details. + rtr.doNotInvalidateC <- struct{}{} + } + + timer.Reset(rl) + + case ok && rl == 0: + // We know about the router but it is no longer to be + // used as a default router so invalidate it. + ndp.invalidateDefaultRouter(ip) + } + } + + // TODO(b/140948104): Do Prefix Discovery. + // TODO(b/141556115): Do Parameter Discovery. +} + +// invalidateDefaultRouter invalidates a discovered default router. +// +// The NIC that ndp belongs to and its associated stack MUST be locked. +func (ndp *ndpState) invalidateDefaultRouter(ip tcpip.Address) { + rtr, ok := ndp.defaultRouters[ip] + + // Is the router still discovered? + if !ok { + // ...Nope, do nothing further. + return + } + + rtr.invalidationTimer.Stop() + rtr.invalidationTimer = nil + close(rtr.doNotInvalidateC) + rtr.doNotInvalidateC = nil + + delete(ndp.defaultRouters, ip) + + // Let the integrator know a discovered default router is invalidated. + if ndp.nic.stack.ndpDisp != nil { + ndp.nic.stack.routeTable = ndp.nic.stack.ndpDisp.OnDefaultRouterInvalidated(ndp.nic.ID(), ip) + } +} + +// rememberDefaultRouter remembers a newly discovered default router with IPv6 +// link-local address ip with lifetime rl. +// +// The router identified by ip MUST NOT already be known by the NIC. +// +// The NIC that ndp belongs to and its associated stack MUST be locked. +func (ndp *ndpState) rememberDefaultRouter(ip tcpip.Address, rl time.Duration) { + if ndp.nic.stack.ndpDisp == nil { + return + } + + // Inform the integrator when we discovered a default router. + remember, routeTable := ndp.nic.stack.ndpDisp.OnDefaultRouterDiscovered(ndp.nic.ID(), ip) + if !remember { + // Informed by the integrator to not remember the router, do + // nothing further. + return + } + + // Used to signal the timer not to invalidate the default router (R) in + // a race condition. See defaultRouterState.doNotInvalidateC for more + // details. + doNotInvalidateC := make(chan struct{}, 1) + + ndp.defaultRouters[ip] = defaultRouterState{ + invalidationTimer: time.AfterFunc(rl, func() { + ndp.nic.stack.mu.Lock() + defer ndp.nic.stack.mu.Unlock() + ndp.nic.mu.Lock() + defer ndp.nic.mu.Unlock() + + select { + case <-doNotInvalidateC: + return + default: + } + + ndp.invalidateDefaultRouter(ip) + }), + doNotInvalidateC: doNotInvalidateC, + } + + ndp.nic.stack.routeTable = routeTable +} |