Fix datarace on TransportEndpointInfo.ID and clean up semantics.

Ensures that all access to TransportEndpointInfo.ID is either:
* In a function ending in a Locked suffix.
* While holding the appropriate mutex.

This primary affects the checkV4Mapped method on affected endpoints, which has
been renamed to checkV4MappedLocked. Also document the method and change its
argument to be a value instead of a pointer which had caused some awkwardness.

This race was possible in the udp and icmp endpoints between Connect and uses
of TransportEndpointInfo.ID including in both itself and Bind.

The tcp endpoint did not suffer from this bug, but benefited from better
documentation.

Updates #357

PiperOrigin-RevId: 298682913

1 files changed, 11 insertions, 12 deletions

diff --git a/pkg/tcpip/transport/icmp/endpoint.go b/pkg/tcpip/transport/icmp/endpoint.go
index 426da1ee6..2a396e9bc 100644
--- a/pkg/tcpip/transport/icmp/endpoint.go
+++ b/pkg/tcpip/transport/icmp/endpoint.go
@@ -291,15 +291,13 @@ func (e *endpoint) write(p tcpip.Payloader, opts tcpip.WriteOptions) (int64, <-c
 			nicID = e.BindNICID
 		}
 
-		toCopy := *to
-		to = &toCopy
-		netProto, err := e.checkV4Mapped(to)
+		dst, netProto, err := e.checkV4MappedLocked(*to)
 		if err != nil {
 			return 0, nil, err
 		}
 
-		// Find the enpoint.
-		r, err := e.stack.FindRoute(nicID, e.BindAddr, to.Addr, netProto, false /* multicastLoop */)
+		// Find the endpoint.
+		r, err := e.stack.FindRoute(nicID, e.BindAddr, dst.Addr, netProto, false /* multicastLoop */)
 		if err != nil {
 			return 0, nil, err
 		}
@@ -480,13 +478,14 @@ func send6(r *stack.Route, ident uint16, data buffer.View, ttl uint8) *tcpip.Err
 	})
 }
 
-func (e *endpoint) checkV4Mapped(addr *tcpip.FullAddress) (tcpip.NetworkProtocolNumber, *tcpip.Error) {
-	unwrapped, netProto, err := e.TransportEndpointInfo.AddrNetProto(*addr, false /* v6only */)
+// checkV4MappedLocked determines the effective network protocol and converts
+// addr to its canonical form.
+func (e *endpoint) checkV4MappedLocked(addr tcpip.FullAddress) (tcpip.FullAddress, tcpip.NetworkProtocolNumber, *tcpip.Error) {
+	unwrapped, netProto, err := e.TransportEndpointInfo.AddrNetProtoLocked(addr, false /* v6only */)
 	if err != nil {
-		return 0, err
+		return tcpip.FullAddress{}, 0, err
 	}
-	*addr = unwrapped
-	return netProto, nil
+	return unwrapped, netProto, nil
 }
 
 // Disconnect implements tcpip.Endpoint.Disconnect.
@@ -517,7 +516,7 @@ func (e *endpoint) Connect(addr tcpip.FullAddress) *tcpip.Error {
 		return tcpip.ErrInvalidEndpointState
 	}
 
-	netProto, err := e.checkV4Mapped(&addr)
+	addr, netProto, err := e.checkV4MappedLocked(addr)
 	if err != nil {
 		return err
 	}
@@ -630,7 +629,7 @@ func (e *endpoint) bindLocked(addr tcpip.FullAddress) *tcpip.Error {
 		return tcpip.ErrInvalidEndpointState
 	}
 
-	netProto, err := e.checkV4Mapped(&addr)
+	addr, netProto, err := e.checkV4MappedLocked(addr)
 	if err != nil {
 		return err
 	}