api: add ring management

Rather than every client reinvent the art of using the Wintun and its
ring buffers, we offer helper structs and functions to unify and
simplify Wintun usage.

Signed-off-by: Simon Rozman <simon@rozman.si>

1 files changed, 213 insertions, 0 deletions

diff --git a/api/session.c b/api/session.c
new file mode 100644
index 0000000..5822cb6
--- /dev/null
+++ b/api/session.c
@@ -0,0 +1,213 @@
+/* SPDX-License-Identifier: GPL-2.0
+ *
+ * Copyright (C) 2018-2020 WireGuard LLC. All Rights Reserved.
+ */
+
+#include "pch.h"
+
+#pragma warning(disable : 4200) /* nonstandard: zero-sized array in struct/union */
+
+#define TUN_ALIGNMENT sizeof(ULONG)
+#define TUN_ALIGN(Size) (((ULONG)(Size) + ((ULONG)TUN_ALIGNMENT - 1)) & ~((ULONG)TUN_ALIGNMENT - 1))
+#define TUN_IS_ALIGNED(Size) (!((ULONG)(Size) & ((ULONG)TUN_ALIGNMENT - 1)))
+#define TUN_MAX_PACKET_SIZE TUN_ALIGN(sizeof(TUN_PACKET) + WINTUN_MAX_IP_PACKET_SIZE)
+#define TUN_RING_CAPACITY(Size) ((Size) - sizeof(TUN_RING) - (TUN_MAX_PACKET_SIZE - TUN_ALIGNMENT))
+#define TUN_RING_SIZE(Capacity) (sizeof(TUN_RING) + (Capacity) + (TUN_MAX_PACKET_SIZE - TUN_ALIGNMENT))
+#define TUN_RING_WRAP(Value, Capacity) ((Value) & (Capacity - 1))
+
+typedef struct _TUN_PACKET
+{
+    ULONG Size;
+    UCHAR _Field_size_bytes_(Size)
+    Data[];
+} TUN_PACKET;
+
+typedef struct _TUN_RING
+{
+    volatile ULONG Head;
+    volatile ULONG Tail;
+    volatile LONG Alertable;
+    UCHAR Data[];
+} TUN_RING;
+
+#define TUN_IOCTL_REGISTER_RINGS CTL_CODE(51820U, 0x970U, METHOD_BUFFERED, FILE_READ_DATA | FILE_WRITE_DATA)
+
+typedef struct _TUN_REGISTER_RINGS
+{
+    struct
+    {
+        ULONG RingSize;
+        TUN_RING *Ring;
+        HANDLE TailMoved;
+    } Send, Receive;
+} TUN_REGISTER_RINGS;
+
+typedef struct _TUN_SESSION
+{
+    ULONG Capacity;
+    TUN_REGISTER_RINGS Descriptor;
+    HANDLE Handle;
+} TUN_SESSION;
+
+WINTUN_STATUS WINAPI
+WintunStartSession(_In_ const WINTUN_ADAPTER *Adapter, _In_ DWORD Capacity, _Out_ TUN_SESSION **Session)
+{
+    HANDLE Heap = GetProcessHeap();
+    *Session = HeapAlloc(Heap, 0, sizeof(TUN_SESSION));
+    if (!*Session)
+        return LOG(WINTUN_LOG_ERR, L"Out of memory"), ERROR_OUTOFMEMORY;
+    const ULONG RingSize = TUN_RING_SIZE(Capacity);
+    DWORD Result;
+    BYTE *AllocatedRegion = VirtualAlloc(0, (size_t)RingSize * 2, MEM_COMMIT | MEM_RESERVE, PAGE_READWRITE);
+    if (!AllocatedRegion)
+    {
+        Result = LOG_LAST_ERROR(L"Failed to allocate ring memory");
+        goto cleanupRings;
+    }
+    (*Session)->Descriptor.Send.RingSize = RingSize;
+    (*Session)->Descriptor.Send.Ring = (TUN_RING *)AllocatedRegion;
+    (*Session)->Descriptor.Send.TailMoved = CreateEventW(SecurityAttributes, FALSE, FALSE, NULL);
+    if (!(*Session)->Descriptor.Send.TailMoved)
+    {
+        Result = LOG_LAST_ERROR(L"Failed to create send event");
+        goto cleanupAllocatedRegion;
+    }
+
+    (*Session)->Descriptor.Receive.RingSize = RingSize;
+    (*Session)->Descriptor.Receive.Ring = (TUN_RING *)(AllocatedRegion + RingSize);
+    (*Session)->Descriptor.Receive.TailMoved = CreateEvent(SecurityAttributes, FALSE, FALSE, NULL);
+    if (!(*Session)->Descriptor.Receive.TailMoved)
+    {
+        Result = LOG_LAST_ERROR(L"Failed to create receive event");
+        goto cleanupSendTailMoved;
+    }
+
+    Result = WintunGetAdapterDeviceObject(Adapter, &(*Session)->Handle);
+    if (Result != ERROR_SUCCESS)
+    {
+        LOG(WINTUN_LOG_ERR, L"Failed to open adapter device object");
+        goto cleanupReceiveTailMoved;
+    }
+    DWORD BytesReturned;
+    if (!DeviceIoControl(
+            (*Session)->Handle,
+            TUN_IOCTL_REGISTER_RINGS,
+            &(*Session)->Descriptor,
+            sizeof(TUN_REGISTER_RINGS),
+            NULL,
+            0,
+            &BytesReturned,
+            NULL))
+    {
+        Result = LOG_LAST_ERROR(L"Failed to perform ioctl");
+        goto cleanupHandle;
+    }
+    (*Session)->Capacity = Capacity;
+    return ERROR_SUCCESS;
+cleanupHandle:
+    CloseHandle((*Session)->Handle);
+cleanupReceiveTailMoved:
+    CloseHandle((*Session)->Descriptor.Receive.TailMoved);
+cleanupSendTailMoved:
+    CloseHandle((*Session)->Descriptor.Send.TailMoved);
+cleanupAllocatedRegion:
+    VirtualFree(AllocatedRegion, 0, MEM_RELEASE);
+cleanupRings:
+    HeapFree(Heap, 0, *Session);
+    *Session = NULL;
+    return Result;
+}
+
+void WINAPI
+WintunEndSession(_In_ TUN_SESSION *Session)
+{
+    SetEvent(Session->Descriptor.Send.TailMoved); // wake the reader if it's sleeping
+    CloseHandle(Session->Handle);
+    CloseHandle(Session->Descriptor.Send.TailMoved);
+    CloseHandle(Session->Descriptor.Receive.TailMoved);
+    VirtualFree(Session->Descriptor.Send.Ring, 0, MEM_RELEASE);
+    HeapFree(GetProcessHeap(), 0, Session);
+}
+
+BOOL WINAPI
+WintunIsPacketAvailable(_In_ TUN_SESSION *Session)
+{
+    return InterlockedGetU(&Session->Descriptor.Send.Ring->Head) !=
+           InterlockedGetU(&Session->Descriptor.Send.Ring->Tail);
+}
+
+WINTUN_STATUS WINAPI
+WintunWaitForPacket(_In_ TUN_SESSION *Session, _In_ DWORD Milliseconds)
+{
+    return WaitForSingleObject(Session->Descriptor.Send.TailMoved, Milliseconds);
+}
+
+WINTUN_STATUS WINAPI
+WintunReceivePackets(_In_ TUN_SESSION *Session, _Inout_ WINTUN_PACKET *Queue)
+{
+    ULONG BuffHead = InterlockedGetU(&Session->Descriptor.Send.Ring->Head);
+    if (BuffHead >= Session->Capacity)
+        return ERROR_HANDLE_EOF;
+
+    for (; Queue; Queue = Queue->Next)
+    {
+        const ULONG BuffTail = InterlockedGetU(&Session->Descriptor.Send.Ring->Tail);
+        if (BuffTail >= Session->Capacity)
+            return ERROR_HANDLE_EOF;
+
+        if (BuffHead == BuffTail)
+            return ERROR_NO_MORE_ITEMS;
+
+        const ULONG BuffContent = TUN_RING_WRAP(BuffTail - BuffHead, Session->Capacity);
+        if (BuffContent < sizeof(TUN_PACKET))
+            return ERROR_INVALID_DATA;
+
+        const TUN_PACKET *Packet = (TUN_PACKET *)&Session->Descriptor.Send.Ring->Data[BuffHead];
+        if (Packet->Size > WINTUN_MAX_IP_PACKET_SIZE)
+            return ERROR_INVALID_DATA;
+
+        const ULONG AlignedPacketSize = TUN_ALIGN(sizeof(TUN_PACKET) + Packet->Size);
+        if (AlignedPacketSize > BuffContent)
+            return ERROR_INVALID_DATA;
+
+        Queue->Size = Packet->Size;
+        memcpy(Queue->Data, Packet->Data, Packet->Size);
+        BuffHead = TUN_RING_WRAP(BuffHead + AlignedPacketSize, Session->Capacity);
+        InterlockedSetU(&Session->Descriptor.Send.Ring->Head, BuffHead);
+    }
+
+    return ERROR_SUCCESS;
+}
+
+WINTUN_STATUS WINAPI
+WintunSendPackets(_In_ TUN_SESSION *Session, _In_ const WINTUN_PACKET *Queue)
+{
+    ULONG BuffTail = InterlockedGetU(&Session->Descriptor.Receive.Ring->Tail);
+    if (BuffTail >= Session->Capacity)
+        return ERROR_HANDLE_EOF;
+
+    for (; Queue; Queue = Queue->Next)
+    {
+        const ULONG PacketSize = Queue->Size;
+        const ULONG AlignedPacketSize = TUN_ALIGN(sizeof(TUN_PACKET) + PacketSize);
+
+        const ULONG BuffHead = InterlockedGetU(&Session->Descriptor.Receive.Ring->Head);
+        if (BuffHead >= Session->Capacity)
+            return ERROR_HANDLE_EOF;
+
+        const ULONG BuffSpace = TUN_RING_WRAP(BuffHead - BuffTail - TUN_ALIGNMENT, Session->Capacity);
+        if (AlignedPacketSize > BuffSpace)
+            return ERROR_BUFFER_OVERFLOW; /* Dropping when ring is full. */
+
+        TUN_PACKET *Packet = (TUN_PACKET *)&Session->Descriptor.Receive.Ring->Data[BuffTail];
+        Packet->Size = PacketSize;
+        memcpy(Packet->Data, Queue->Data, PacketSize);
+        BuffTail = TUN_RING_WRAP(BuffTail + AlignedPacketSize, Session->Capacity);
+        InterlockedSetU(&Session->Descriptor.Receive.Ring->Tail, BuffTail);
+
+        if (InterlockedGet(&Session->Descriptor.Receive.Ring->Alertable))
+            SetEvent(Session->Descriptor.Receive.TailMoved);
+    }
+
+    return ERROR_SUCCESS;
+}