diff options
Diffstat (limited to 'pkg/tcpip/stack/ndp.go')
| -rwxr-xr-x | pkg/tcpip/stack/ndp.go | 309 |
1 files changed, 285 insertions, 24 deletions
diff --git a/pkg/tcpip/stack/ndp.go b/pkg/tcpip/stack/ndp.go index 8e49f7a56..8357dca77 100755 --- a/pkg/tcpip/stack/ndp.go +++ b/pkg/tcpip/stack/ndp.go @@ -46,11 +46,18 @@ const ( // defaultDiscoverDefaultRouters is the default configuration for // whether or not to discover default routers from incoming Router - // Advertisements as a host. + // Advertisements, as a host. // // Default = true. defaultDiscoverDefaultRouters = true + // defaultDiscoverOnLinkPrefixes is the default configuration for + // whether or not to discover on-link prefixes from incoming Router + // Advertisements' Prefix Information option, as a host. + // + // Default = true. + defaultDiscoverOnLinkPrefixes = 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 @@ -72,6 +79,14 @@ const ( // // Max = 10. MaxDiscoveredDefaultRouters = 10 + + // MaxDiscoveredOnLinkPrefixes is the maximum number of discovered + // on-link prefixes. The stack should stop discovering new on-link + // prefixes after discovering MaxDiscoveredOnLinkPrefixes on-link + // prefixes. + // + // Max = 10. + MaxDiscoveredOnLinkPrefixes = 10 ) // NDPDispatcher is the interface integrators of netstack must implement to @@ -106,6 +121,24 @@ type NDPDispatcher interface { // 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 + + // OnOnLinkPrefixDiscovered will be called when a new on-link prefix is + // discovered. Implementations must return true along with a new valid + // route table if the newly discovered on-link prefix 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. + OnOnLinkPrefixDiscovered(nicID tcpip.NICID, prefix tcpip.Subnet) (bool, []tcpip.Route) + + // OnOnLinkPrefixInvalidated will be called when a discovered on-link + // prefix 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. + OnOnLinkPrefixInvalidated(nicID tcpip.NICID, prefix tcpip.Subnet) []tcpip.Route } // NDPConfigurations is the NDP configurations for the netstack. @@ -130,6 +163,11 @@ type NDPConfigurations struct { // be discovered from Router Advertisements. This configuration is // ignored if HandleRAs is false. DiscoverDefaultRouters bool + + // DiscoverOnLinkPrefixes determines whether or not on-link prefixes + // will be discovered from Router Advertisements' Prefix Information + // option. This configuration is ignored if HandleRAs is false. + DiscoverOnLinkPrefixes bool } // DefaultNDPConfigurations returns an NDPConfigurations populated with @@ -140,6 +178,7 @@ func DefaultNDPConfigurations() NDPConfigurations { RetransmitTimer: defaultRetransmitTimer, HandleRAs: defaultHandleRAs, DiscoverDefaultRouters: defaultDiscoverDefaultRouters, + DiscoverOnLinkPrefixes: defaultDiscoverOnLinkPrefixes, } } @@ -167,6 +206,10 @@ type ndpState struct { // The default routers discovered through Router Advertisements. defaultRouters map[tcpip.Address]defaultRouterState + + // The on-link prefixes discovered through Router Advertisements' Prefix + // Information option. + onLinkPrefixes map[tcpip.Subnet]onLinkPrefixState } // dadState holds the Duplicate Address Detection timer and channel to signal @@ -183,11 +226,11 @@ type dadState struct { } // defaultRouterState holds data associated with a default router discovered by -// a Router Advertisement. +// a Router Advertisement (RA). type defaultRouterState struct { invalidationTimer *time.Timer - // Used to signal the timer not to invalidate the default router (R) in + // Used to inform 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 @@ -198,10 +241,33 @@ type defaultRouterState struct { // 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{} + // inform the timer using doNotInvalidate to not invalidate R, so that + // once T2 obtains the lock, it will see that it is set to true and do + // nothing further. + doNotInvalidate *bool +} + +// onLinkPrefixState holds data associated with an on-link prefix discovered by +// a Router Advertisement's Prefix Information option (PI) when the NDP +// configurations was configured to do so. +type onLinkPrefixState struct { + invalidationTimer *time.Timer + + // Used to signal the timer not to invalidate the on-link prefix (P) in + // a race condition (T1 is a goroutine that handles a PI for P and T2 + // is the goroutine that handles P's invalidation timer firing): + // T1: Receive a new PI for P + // T1: Obtain the NIC's lock before processing the PI + // T2: P's invalidation timer fires, and gets blocked on obtaining the + // NIC's lock + // T1: Refreshes/extends P's lifetime & releases NIC's lock + // T2: Obtains NIC's lock & invalidates P immediately + // + // To resolve this, T1 will check to see if the timer already fired, and + // inform the timer using doNotInvalidate to not invalidate P, so that + // once T2 obtains the lock, it will see that it is set to true and do + // nothing further. + doNotInvalidate *bool } // startDuplicateAddressDetection performs Duplicate Address Detection. @@ -440,14 +506,13 @@ func (ndp *ndpState) handleRA(ip tcpip.Address, ra header.NDPRouterAdvert) { 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 + // lock. Inform the timer not to invalidate the + // router when it obtains the lock as we just + // got a new RA that refreshes its lifetime to a + // non-zero value. See + // defaultRouterState.doNotInvalidate for more // details. - rtr.doNotInvalidateC <- struct{}{} + *rtr.doNotInvalidate = true } timer.Reset(rl) @@ -459,8 +524,117 @@ func (ndp *ndpState) handleRA(ip tcpip.Address, ra header.NDPRouterAdvert) { } } - // TODO(b/140948104): Do Prefix Discovery. - // TODO(b/141556115): Do Parameter Discovery. + // TODO(b/141556115): Do (RetransTimer, ReachableTime)) Parameter + // Discovery. + + // We know the options is valid as far as wire format is concerned since + // we got the Router Advertisement, as documented by this fn. Given this + // we do not check the iterator for errors on calls to Next. + it, _ := ra.Options().Iter(false) + for opt, done, _ := it.Next(); !done; opt, done, _ = it.Next() { + switch opt.Type() { + case header.NDPPrefixInformationType: + if !ndp.configs.DiscoverOnLinkPrefixes { + continue + } + + pi := opt.(header.NDPPrefixInformation) + + prefix := pi.Subnet() + + // Is the prefix a link-local? + if header.IsV6LinkLocalAddress(prefix.ID()) { + // ...Yes, skip as per RFC 4861 section 6.3.4. + continue + } + + // Is the Prefix Length 0? + if prefix.Prefix() == 0 { + // ...Yes, skip as this is an invalid prefix + // as all IPv6 addresses cannot be on-link. + continue + } + + if !pi.OnLinkFlag() { + // Not on-link so don't "discover" it as an + // on-link prefix. + continue + } + + prefixState, ok := ndp.onLinkPrefixes[prefix] + vl := pi.ValidLifetime() + switch { + case !ok && vl == 0: + // Don't know about this prefix but has a zero + // valid lifetime, so just ignore. + continue + + case !ok && vl != 0: + // This is a new on-link prefix we are + // discovering. + // + // Only remember it if we currently know about + // less than MaxDiscoveredOnLinkPrefixes on-link + // prefixes. + if len(ndp.onLinkPrefixes) < MaxDiscoveredOnLinkPrefixes { + ndp.rememberOnLinkPrefix(prefix, vl) + } + continue + + case ok && vl == 0: + // We know about the on-link prefix, but it is + // no longer to be considered on-link, so + // invalidate it. + ndp.invalidateOnLinkPrefix(prefix) + continue + } + + // This is an already discovered on-link prefix with a + // new non-zero valid lifetime. + // Update the invalidation timer. + timer := prefixState.invalidationTimer + + if timer == nil && vl >= header.NDPPrefixInformationInfiniteLifetime { + // Had infinite valid lifetime before and + // continues to have an invalid lifetime. Do + // nothing further. + continue + } + + if timer != nil && !timer.Stop() { + // If we reach this point, then we know the + // timer already fired after we took the NIC + // lock. Inform the timer to not invalidate + // the prefix once it obtains the lock as we + // just got a new PI that refeshes its lifetime + // to a non-zero value. See + // onLinkPrefixState.doNotInvalidate for more + // details. + *prefixState.doNotInvalidate = true + } + + if vl >= header.NDPPrefixInformationInfiniteLifetime { + // Prefix is now valid forever so we don't need + // an invalidation timer. + prefixState.invalidationTimer = nil + ndp.onLinkPrefixes[prefix] = prefixState + continue + } + + if timer != nil { + // We already have a timer so just reset it to + // expire after the new valid lifetime. + timer.Reset(vl) + continue + } + + // We do not have a timer so just create a new one. + prefixState.invalidationTimer = ndp.prefixInvalidationCallback(prefix, vl, prefixState.doNotInvalidate) + ndp.onLinkPrefixes[prefix] = prefixState + } + + // TODO(b/141556115): Do (MTU) Parameter Discovery. + } } // invalidateDefaultRouter invalidates a discovered default router. @@ -477,8 +651,8 @@ func (ndp *ndpState) invalidateDefaultRouter(ip tcpip.Address) { rtr.invalidationTimer.Stop() rtr.invalidationTimer = nil - close(rtr.doNotInvalidateC) - rtr.doNotInvalidateC = nil + *rtr.doNotInvalidate = true + rtr.doNotInvalidate = nil delete(ndp.defaultRouters, ip) @@ -508,9 +682,9 @@ func (ndp *ndpState) rememberDefaultRouter(ip tcpip.Address, rl time.Duration) { } // Used to signal the timer not to invalidate the default router (R) in - // a race condition. See defaultRouterState.doNotInvalidateC for more + // a race condition. See defaultRouterState.doNotInvalidate for more // details. - doNotInvalidateC := make(chan struct{}, 1) + var doNotInvalidate bool ndp.defaultRouters[ip] = defaultRouterState{ invalidationTimer: time.AfterFunc(rl, func() { @@ -519,16 +693,103 @@ func (ndp *ndpState) rememberDefaultRouter(ip tcpip.Address, rl time.Duration) { ndp.nic.mu.Lock() defer ndp.nic.mu.Unlock() - select { - case <-doNotInvalidateC: + if doNotInvalidate { + doNotInvalidate = false return - default: } ndp.invalidateDefaultRouter(ip) }), - doNotInvalidateC: doNotInvalidateC, + doNotInvalidate: &doNotInvalidate, + } + + ndp.nic.stack.routeTable = routeTable +} + +// rememberOnLinkPrefix remembers a newly discovered on-link prefix with IPv6 +// address with prefix prefix with lifetime l. +// +// The prefix identified by prefix MUST NOT already be known. +// +// The NIC that ndp belongs to and its associated stack MUST be locked. +func (ndp *ndpState) rememberOnLinkPrefix(prefix tcpip.Subnet, l time.Duration) { + if ndp.nic.stack.ndpDisp == nil { + return + } + + // Inform the integrator when we discovered an on-link prefix. + remember, routeTable := ndp.nic.stack.ndpDisp.OnOnLinkPrefixDiscovered(ndp.nic.ID(), prefix) + if !remember { + // Informed by the integrator to not remember the prefix, do + // nothing further. + return + } + + // Used to signal the timer not to invalidate the on-link prefix (P) in + // a race condition. See onLinkPrefixState.doNotInvalidate for more + // details. + var doNotInvalidate bool + var timer *time.Timer + + // Only create a timer if the lifetime is not infinite. + if l < header.NDPPrefixInformationInfiniteLifetime { + timer = ndp.prefixInvalidationCallback(prefix, l, &doNotInvalidate) + } + + ndp.onLinkPrefixes[prefix] = onLinkPrefixState{ + invalidationTimer: timer, + doNotInvalidate: &doNotInvalidate, } ndp.nic.stack.routeTable = routeTable } + +// invalidateOnLinkPrefix invalidates a discovered on-link prefix. +// +// The NIC that ndp belongs to and its associated stack MUST be locked. +func (ndp *ndpState) invalidateOnLinkPrefix(prefix tcpip.Subnet) { + s, ok := ndp.onLinkPrefixes[prefix] + + // Is the on-link prefix still discovered? + if !ok { + // ...Nope, do nothing further. + return + } + + if s.invalidationTimer != nil { + s.invalidationTimer.Stop() + s.invalidationTimer = nil + *s.doNotInvalidate = true + } + + s.doNotInvalidate = nil + + delete(ndp.onLinkPrefixes, prefix) + + // Let the integrator know a discovered on-link prefix is invalidated. + if ndp.nic.stack.ndpDisp != nil { + ndp.nic.stack.routeTable = ndp.nic.stack.ndpDisp.OnOnLinkPrefixInvalidated(ndp.nic.ID(), prefix) + } +} + +// prefixInvalidationCallback returns a new on-link prefix invalidation timer +// for prefix that fires after vl. +// +// doNotInvalidate is used to signal the timer when it fires at the same time +// that a prefix's valid lifetime gets refreshed. See +// onLinkPrefixState.doNotInvalidate for more details. +func (ndp *ndpState) prefixInvalidationCallback(prefix tcpip.Subnet, vl time.Duration, doNotInvalidate *bool) *time.Timer { + return time.AfterFunc(vl, func() { + ndp.nic.stack.mu.Lock() + defer ndp.nic.stack.mu.Unlock() + ndp.nic.mu.Lock() + defer ndp.nic.mu.Unlock() + + if *doNotInvalidate { + *doNotInvalidate = false + return + } + + ndp.invalidateOnLinkPrefix(prefix) + }) +} |