From fbf89789b80d564c2bdeb3d4643eb899223d17c9 Mon Sep 17 00:00:00 2001
From: Brad Fitzpatrick <bradfitz@tailscale.com>
Date: Tue, 4 Aug 2020 17:04:02 -0700
Subject: [PATCH] wgengine/magicsock: don't deadlock on pre-disco Endpoints w/
 lazy wireguard configs

Fixes tailscale/tailscale#637

(cherry picked from commit 7c38db0c971b450636841a8b9be5ae5c00b1f1f2)
---
 wgengine/magicsock/magicsock.go | 12 +++++-------
 1 file changed, 5 insertions(+), 7 deletions(-)

diff --git a/wgengine/magicsock/magicsock.go b/wgengine/magicsock/magicsock.go
index 587f4f72d..e842eb3cd 100644
--- a/wgengine/magicsock/magicsock.go
+++ b/wgengine/magicsock/magicsock.go
@@ -2626,16 +2626,17 @@ func (c *Conn) CreateEndpoint(pubKey [32]byte, addrs string) (conn.Endpoint, err
 	pk := key.Public(pubKey)
 	c.logf("magicsock: CreateEndpoint: key=%s: %s", pk.ShortString(), derpStr(addrs))
 
+	if !c.canCreateEPUnlocked.Get() { // sorry
+		c.mu.Lock()
+		defer c.mu.Unlock()
+	}
+
 	if strings.HasSuffix(addrs, controlclient.EndpointDiscoSuffix) {
 		discoHex := strings.TrimSuffix(addrs, controlclient.EndpointDiscoSuffix)
 		discoKey, err := key.NewPublicFromHexMem(mem.S(discoHex))
 		if err != nil {
 			return nil, fmt.Errorf("magicsock: invalid discokey endpoint %q for %v: %w", addrs, pk.ShortString(), err)
 		}
-		if !c.canCreateEPUnlocked.Get() { // sorry
-			c.mu.Lock()
-			defer c.mu.Unlock()
-		}
 		de := &discoEndpoint{
 			c:                  c,
 			publicKey:          tailcfg.NodeKey(pk),        // peer public key (for WireGuard + DERP)
@@ -2679,9 +2680,6 @@ func (c *Conn) CreateEndpoint(pubKey [32]byte, addrs string) (conn.Endpoint, err
 		}
 	}
 
-	c.mu.Lock()
-	defer c.mu.Unlock()
-
 	// If this endpoint is being updated, remember its old set of
 	// endpoints so we can remove any (from c.addrsByUDP) that are
 	// not in the new set.