Handle removed NIC in NDP timer for packet tx

NDP packets are sent periodically from NDP timers. These timers do not
hold the NIC lock when sending packets as the packet write operation
may take some time. While the lock is not held, the NIC may be removed
by some other goroutine. This change handles that scenario gracefully.

Test: stack_test.TestRemoveNICWhileHandlingRSTimer
PiperOrigin-RevId: 315524143

1 files changed, 4 insertions, 0 deletions

diff --git a/pkg/tcpip/stack/route.go b/pkg/tcpip/stack/route.go
index f5b6ca0b9..d65f8049e 100644
--- a/pkg/tcpip/stack/route.go
+++ b/pkg/tcpip/stack/route.go
@@ -113,6 +113,8 @@ func (r *Route) GSOMaxSize() uint32 {
 // If address resolution is required, ErrNoLinkAddress and a notification channel is
 // returned for the top level caller to block. Channel is closed once address resolution
 // is complete (success or not).
+//
+// The NIC r uses must not be locked.
 func (r *Route) Resolve(waker *sleep.Waker) (<-chan struct{}, *tcpip.Error) {
 	if !r.IsResolutionRequired() {
 		// Nothing to do if there is no cache (which does the resolution on cache miss) or
@@ -148,6 +150,8 @@ func (r *Route) RemoveWaker(waker *sleep.Waker) {
 
 // IsResolutionRequired returns true if Resolve() must be called to resolve
 // the link address before the this route can be written to.
+//
+// The NIC r uses must not be locked.
 func (r *Route) IsResolutionRequired() bool {
 	return r.ref.isValidForOutgoing() && r.ref.linkCache != nil && r.RemoteLinkAddress == ""
 }