device: use atomic access for unlocked keypair.next

Go's GC semantics might not always guarantee the safety of this, and the
race detector gets upset too, so instead we wrap this all in atomic
accessors.

Reported-by: David Anderson <danderson@tailscale.com>
Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>

1 files changed, 10 insertions, 0 deletions

diff --git a/device/keypair.go b/device/keypair.go
index 9c78fa9..d70c7f4 100644
--- a/device/keypair.go
+++ b/device/keypair.go
@@ -8,7 +8,9 @@ package device
 import (
 	"crypto/cipher"
 	"sync"
+	"sync/atomic"
 	"time"
+	"unsafe"
 
 	"golang.zx2c4.com/wireguard/replay"
 )
@@ -38,6 +40,14 @@ type Keypairs struct {
 	next     *Keypair
 }
 
+func (kp *Keypairs) storeNext(next *Keypair) {
+	atomic.StorePointer((*unsafe.Pointer)((unsafe.Pointer)(&kp.next)), (unsafe.Pointer)(next))
+}
+
+func (kp *Keypairs) loadNext() *Keypair {
+	return (*Keypair)(atomic.LoadPointer((*unsafe.Pointer)((unsafe.Pointer)(&kp.next))))
+}
+
 func (kp *Keypairs) Current() *Keypair {
 	kp.RLock()
 	defer kp.RUnlock()