From b28bd31bb6d920c23b5036d94bc7123143369e24 Mon Sep 17 00:00:00 2001
From: Ghanan Gowripalan <ghanan@google.com>
Date: Thu, 16 Sep 2021 20:04:00 -0700
Subject: Allow creating packet socket bound to any protocol

...even protocols the stack is unaware of.

While I am here, annotate checklocks on stack.packetEndpointList.

PiperOrigin-RevId: 397226754
---
 pkg/tcpip/stack/nic.go | 20 +++++++++++++-------
 1 file changed, 13 insertions(+), 7 deletions(-)

(limited to 'pkg/tcpip/stack')

diff --git a/pkg/tcpip/stack/nic.go b/pkg/tcpip/stack/nic.go
index ab7e1d859..29d580e76 100644
--- a/pkg/tcpip/stack/nic.go
+++ b/pkg/tcpip/stack/nic.go
@@ -97,6 +97,8 @@ type packetEndpointList struct {
 	mu sync.RWMutex
 
 	// eps is protected by mu, but the contained PacketEndpoint values are not.
+	//
+	// +checklocks:mu
 	eps []PacketEndpoint
 }
 
@@ -117,6 +119,12 @@ func (p *packetEndpointList) remove(ep PacketEndpoint) {
 	}
 }
 
+func (p *packetEndpointList) len() int {
+	p.mu.RLock()
+	defer p.mu.RUnlock()
+	return len(p.eps)
+}
+
 // forEach calls fn with each endpoints in p while holding the read lock on p.
 func (p *packetEndpointList) forEach(fn func(PacketEndpoint)) {
 	p.mu.RLock()
@@ -157,14 +165,8 @@ func newNIC(stack *Stack, id tcpip.NICID, name string, ep LinkEndpoint, ctx NICC
 
 	resolutionRequired := ep.Capabilities()&CapabilityResolutionRequired != 0
 
-	// Register supported packet and network endpoint protocols.
-	for _, netProto := range header.Ethertypes {
-		nic.packetEPs.eps[netProto] = new(packetEndpointList)
-	}
 	for _, netProto := range stack.networkProtocols {
 		netNum := netProto.Number()
-		nic.packetEPs.eps[netNum] = new(packetEndpointList)
-
 		netEP := netProto.NewEndpoint(nic, nic)
 		nic.networkEndpoints[netNum] = netEP
 
@@ -974,7 +976,8 @@ func (n *nic) registerPacketEndpoint(netProto tcpip.NetworkProtocolNumber, ep Pa
 
 	eps, ok := n.packetEPs.eps[netProto]
 	if !ok {
-		return &tcpip.ErrNotSupported{}
+		eps = new(packetEndpointList)
+		n.packetEPs.eps[netProto] = eps
 	}
 	eps.add(ep)
 
@@ -990,6 +993,9 @@ func (n *nic) unregisterPacketEndpoint(netProto tcpip.NetworkProtocolNumber, ep
 		return
 	}
 	eps.remove(ep)
+	if eps.len() == 0 {
+		delete(n.packetEPs.eps, netProto)
+	}
 }
 
 // isValidForOutgoing returns true if the endpoint can be used to send out a
-- 
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