Replace GoString with our own function to fix mte issue

Co-authored-by: Joakim Hulthe <joakim@hulthe.net>

4 files changed, 26 insertions, 4 deletions

diff --git a/wireguard-go-rs/libwg/libwg.go b/wireguard-go-rs/libwg/libwg.go
index aaa03ef838..6cfbd0ba55 100644
--- a/wireguard-go-rs/libwg/libwg.go
+++ b/wireguard-go-rs/libwg/libwg.go
@@ -97,7 +97,7 @@ func wgSetConfig(tunnelHandle int32, cSettings *C.char) C.int32_t {
 		tunnel.Logger.Errorf("cSettings is null\n")
 		return ERROR_INVALID_ARGUMENT
 	}
-	settings := C.GoString(cSettings)
+	settings := goStringFixed(cSettings)
 
 	setError := tunnel.Device.IpcSetOperation(bufio.NewReader(strings.NewReader(settings)))
 	if setError != nil {
@@ -114,3 +114,24 @@ func wgFreePtr(ptr unsafe.Pointer) {
 }
 
 func main() {}
+
+//Instead of using the normal version of C.GoString we need to use the version that takes
+//a length argument (C.GoStringN). That is because the normal C.GoString reads a whole
+//page of memory to determine the length of the string. This causes a crash if
+//mte is turned on. So instead we determine the length of the c string by reading
+//each character until we reach the end of the string.
+func goStringFixed(cString *C.char) string {
+	ptr := unsafe.Pointer(cString)
+	i := 0
+	for {
+		byte := (*C.char)(unsafe.Pointer(uintptr(ptr) + uintptr(i)))
+
+		if *byte == 0 {
+			break
+		}
+
+		i += 1
+	}
+
+	return C.GoStringN(cString, C.int(i))
+}
diff --git a/wireguard-go-rs/libwg/libwg_android.go b/wireguard-go-rs/libwg/libwg_android.go
index 86410721f5..d623b7711d 100644
--- a/wireguard-go-rs/libwg/libwg_android.go
+++ b/wireguard-go-rs/libwg/libwg_android.go
@@ -37,7 +37,8 @@ func wgTurnOn(cSettings *C.char, fd int, logSink LogSink, logContext LogContext)
 		logger.Errorf("cSettings is null\n")
 		return ERROR_INVALID_ARGUMENT
 	}
-	settings := C.GoString(cSettings)
+
+	settings := goStringFixed(cSettings)
 
 	tunDevice, _, err := tun.CreateUnmonitoredTUNFromFD(fd)
 	if err != nil {
diff --git a/wireguard-go-rs/libwg/libwg_daita.go b/wireguard-go-rs/libwg/libwg_daita.go
index d5f8f132ed..3b1fedda4c 100644
--- a/wireguard-go-rs/libwg/libwg_daita.go
+++ b/wireguard-go-rs/libwg/libwg_daita.go
@@ -38,7 +38,7 @@ func wgActivateDaita(tunnelHandle C.int32_t, peerPubkey *C.uint8_t, machines *C.
 		return ERROR_UNKNOWN_PEER
 	}
 
-	if !peer.EnableDaita(C.GoString((*C.char)(machines)), uint(eventsCapacity), uint(actionsCapacity), maxPaddingBytes, maxBlockingBytes) {
+	if !peer.EnableDaita(goStringFixed((*C.char)(machines)), uint(eventsCapacity), uint(actionsCapacity), maxPaddingBytes, maxBlockingBytes) {
 		return ERROR_ENABLE_DAITA
 	}
 
diff --git a/wireguard-go-rs/libwg/libwg_default.go b/wireguard-go-rs/libwg/libwg_default.go
index 6741de715f..263c231a61 100644
--- a/wireguard-go-rs/libwg/libwg_default.go
+++ b/wireguard-go-rs/libwg/libwg_default.go
@@ -40,7 +40,7 @@ func wgTurnOn(mtu int, cSettings *C.char, fd int, logSink LogSink, logContext Lo
 		logger.Errorf("cSettings is null\n")
 		return ERROR_INVALID_ARGUMENT
 	}
-	settings := C.GoString(cSettings)
+	settings := goStringFixed(cSettings)
 
 	file := os.NewFile(uintptr(fd), "")
 	tunDevice, err := tun.CreateTUNFromFile(file, mtu)