device: fix possible deadlock in close methodmaster

There is a possible deadlock in `device.Close()` when you try to close
the device very soon after its start. The problem is that two different
methods acquire the same locks in different order:

1. device.Close()
 - device.ipcMutex.Lock()
 - device.state.Lock()

2. device.changeState(deviceState)
 - device.state.Lock()
 - device.ipcMutex.Lock()

Reproducer:

    func TestDevice_deadlock(t *testing.T) {
    	d := randDevice(t)
    	d.Close()
    }

Problem:

    $ go clean -testcache && go test -race -timeout 3s -run TestDevice_deadlock ./device | grep -A 10 sync.runtime_SemacquireMutex
    sync.runtime_SemacquireMutex(0xc000117d20?, 0x94?, 0x0?)
            /usr/local/opt/go/libexec/src/runtime/sema.go:77 +0x25
    sync.(*Mutex).lockSlow(0xc000130518)
            /usr/local/opt/go/libexec/src/sync/mutex.go:171 +0x213
    sync.(*Mutex).Lock(0xc000130518)
            /usr/local/opt/go/libexec/src/sync/mutex.go:90 +0x55
    golang.zx2c4.com/wireguard/device.(*Device).Close(0xc000130500)
            /Users/martin.basovnik/git/basovnik/wireguard-go/device/device.go:373 +0xb6
    golang.zx2c4.com/wireguard/device.TestDevice_deadlock(0x0?)
            /Users/martin.basovnik/git/basovnik/wireguard-go/device/device_test.go:480 +0x2c
    testing.tRunner(0xc00014c000, 0x131d7b0)
    --
    sync.runtime_SemacquireMutex(0xc000130564?, 0x60?, 0xc000130548?)
            /usr/local/opt/go/libexec/src/runtime/sema.go:77 +0x25
    sync.(*Mutex).lockSlow(0xc000130750)
            /usr/local/opt/go/libexec/src/sync/mutex.go:171 +0x213
    sync.(*Mutex).Lock(0xc000130750)
            /usr/local/opt/go/libexec/src/sync/mutex.go:90 +0x55
    sync.(*RWMutex).Lock(0xc000130750)
            /usr/local/opt/go/libexec/src/sync/rwmutex.go:147 +0x45
    golang.zx2c4.com/wireguard/device.(*Device).upLocked(0xc000130500)
            /Users/martin.basovnik/git/basovnik/wireguard-go/device/device.go:179 +0x72
    golang.zx2c4.com/wireguard/device.(*Device).changeState(0xc000130500, 0x1)

Signed-off-by: Martin Basovnik <martin.basovnik@gmail.com>
Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>

1 files changed, 2 insertions, 2 deletions

diff --git a/device/device.go b/device/device.go
index ca26d00..83c33ee 100644
--- a/device/device.go
+++ b/device/device.go
@@ -368,10 +368,10 @@ func (device *Device) RemoveAllPeers() {
 }
 
 func (device *Device) Close() {
-	device.ipcMutex.Lock()
-	defer device.ipcMutex.Unlock()
 	device.state.Lock()
 	defer device.state.Unlock()
+	device.ipcMutex.Lock()
+	defer device.ipcMutex.Unlock()
 	if device.isClosed() {
 		return
 	}