wintun: ring buffers based I/O

Implemented according to Wintun documentation
and reference client code.

Wintun uses ring buffers to communicate between
kernel driver and user process. Client allocates
send and receive ring buffers, creates events
and passes it to kernel driver under LocalSystem
privileges.

When data is available for read, wintun modifies
"tail" pointer of send ring and signals via event.
User process reads data from "head" to "tail" and
updates "head" pointer.

When user process is ready to write, it writes
to receive ring, updates "tail" pointer and signals
to kernel via event.

In openvpn code we add send ring's event to event loop.
Before performing io wait, we compare "head" and "tail"
pointers of send ring and if they're different, we skip
io wait and perform read.

This also adds ring buffers support to tcp and udp
server code.

Signed-off-by: Lev Stipakov <lev@openvpn.net>
Acked-by: Steffan Karger <steffan.karger@fox-it.com>
Acked-by: Simon Rozman <simon@rozman.si>
Message-Id: <20191217124410.81-1-lstipakov@gmail.com>
URL: https://www.mail-archive.com/openvpn-devel@lists.sourceforge.net/msg19243.html
Signed-off-by: Gert Doering <gert@greenie.muc.de>

1 files changed, 167 insertions, 2 deletions

diff --git a/src/openvpn/tun.h b/src/openvpn/tun.h
index 66b75d9..10f687c 100644
--- a/src/openvpn/tun.h
+++ b/src/openvpn/tun.h
@@ -182,6 +182,9 @@ struct tuntap
 
     bool wintun; /* true if wintun is used instead of tap-windows6 */
     int standby_iter;
+
+    struct tun_ring *wintun_send_ring;
+    struct tun_ring *wintun_receive_ring;
 #else  /* ifdef _WIN32 */
     int fd; /* file descriptor for TUN/TAP dev */
 #endif
@@ -211,6 +214,20 @@ tuntap_defined(const struct tuntap *tt)
 #endif
 }
 
+#ifdef _WIN32
+inline bool
+tuntap_is_wintun(struct tuntap *tt)
+{
+    return tt && tt->wintun;
+}
+
+inline bool
+tuntap_ring_empty(struct tuntap *tt)
+{
+    return tuntap_is_wintun(tt) && (tt->wintun_send_ring->head == tt->wintun_send_ring->tail);
+}
+#endif
+
 /*
  * Function prototypes
  */
@@ -478,10 +495,158 @@ read_tun_buffered(struct tuntap *tt, struct buffer *buf)
     return tun_finalize(tt->hand, &tt->reads, buf);
 }
 
+static inline ULONG
+wintun_ring_packet_align(ULONG size)
+{
+    return (size + (WINTUN_PACKET_ALIGN - 1)) & ~(WINTUN_PACKET_ALIGN - 1);
+}
+
+static inline ULONG
+wintun_ring_wrap(ULONG value)
+{
+    return value & (WINTUN_RING_CAPACITY - 1);
+}
+
+static inline void
+read_wintun(struct tuntap *tt, struct buffer* buf)
+{
+    struct tun_ring *ring = tt->wintun_send_ring;
+    ULONG head = ring->head;
+    ULONG tail = ring->tail;
+    ULONG content_len;
+    struct TUN_PACKET *packet;
+    ULONG aligned_packet_size;
+
+    *buf = tt->reads.buf_init;
+    buf->len = 0;
+
+    if ((head >= WINTUN_RING_CAPACITY) || (tail >= WINTUN_RING_CAPACITY))
+    {
+        msg(M_INFO, "Wintun: ring capacity exceeded");
+        buf->len = -1;
+        return;
+    }
+
+    if (head == tail)
+    {
+        /* nothing to read */
+        return;
+    }
+
+    content_len = wintun_ring_wrap(tail - head);
+    if (content_len < sizeof(struct TUN_PACKET_HEADER))
+    {
+        msg(M_INFO, "Wintun: incomplete packet header in send ring");
+        buf->len = -1;
+        return;
+    }
+
+    packet = (struct TUN_PACKET *) &ring->data[head];
+    if (packet->size > WINTUN_MAX_PACKET_SIZE)
+    {
+        msg(M_INFO, "Wintun: packet too big in send ring");
+        buf->len = -1;
+        return;
+    }
+
+    aligned_packet_size = wintun_ring_packet_align(sizeof(struct TUN_PACKET_HEADER) + packet->size);
+    if (aligned_packet_size > content_len)
+    {
+        msg(M_INFO, "Wintun: incomplete packet in send ring");
+        buf->len = -1;
+        return;
+    }
+
+    buf_write(buf, packet->data, packet->size);
+
+    head = wintun_ring_wrap(head + aligned_packet_size);
+    ring->head = head;
+}
+
+static inline bool
+is_ip_packet_valid(const struct buffer *buf)
+{
+    const struct openvpn_iphdr* ih = (const struct openvpn_iphdr *)BPTR(buf);
+
+    if (OPENVPN_IPH_GET_VER(ih->version_len) == 4)
+    {
+        if (BLEN(buf) < sizeof(struct openvpn_iphdr))
+        {
+            return false;
+        }
+    }
+    else if (OPENVPN_IPH_GET_VER(ih->version_len) == 6)
+    {
+        if (BLEN(buf) < sizeof(struct openvpn_ipv6hdr))
+        {
+            return false;
+        }
+    }
+    else
+    {
+        return false;
+    }
+
+    return true;
+}
+
+static inline int
+write_wintun(struct tuntap *tt, struct buffer *buf)
+{
+    struct tun_ring *ring = tt->wintun_receive_ring;
+    ULONG head = ring->head;
+    ULONG tail = ring->tail;
+    ULONG aligned_packet_size;
+    ULONG buf_space;
+    struct TUN_PACKET *packet;
+
+    /* wintun marks ring as corrupted (overcapacity) if it receives invalid IP packet */
+    if (!is_ip_packet_valid(buf))
+    {
+        msg(D_LOW, "write_wintun(): drop invalid IP packet");
+        return 0;
+    }
+
+    if ((head >= WINTUN_RING_CAPACITY) || (tail >= WINTUN_RING_CAPACITY))
+    {
+        msg(M_INFO, "write_wintun(): head/tail value is over capacity");
+        return -1;
+    }
+
+    aligned_packet_size = wintun_ring_packet_align(sizeof(struct TUN_PACKET_HEADER) + BLEN(buf));
+    buf_space = wintun_ring_wrap(head - tail - WINTUN_PACKET_ALIGN);
+    if (aligned_packet_size > buf_space)
+    {
+        msg(M_INFO, "write_wintun(): ring is full");
+        return 0;
+    }
+
+    /* copy packet size and data into ring */
+    packet = (struct TUN_PACKET* )&ring->data[tail];
+    packet->size = BLEN(buf);
+    memcpy(packet->data, BPTR(buf), BLEN(buf));
+
+    /* move ring tail */
+    ring->tail = wintun_ring_wrap(tail + aligned_packet_size);
+    if (ring->alertable != 0)
+    {
+        SetEvent(tt->rw_handle.write);
+    }
+
+    return BLEN(buf);
+}
+
 static inline int
 write_tun_buffered(struct tuntap *tt, struct buffer *buf)
 {
-    return tun_write_win32(tt, buf);
+    if (tt->wintun)
+    {
+        return write_wintun(tt, buf);
+    }
+    else
+    {
+        return tun_write_win32(tt, buf);
+    }
 }
 
 #else  /* ifdef _WIN32 */
@@ -544,7 +709,7 @@ tun_set(struct tuntap *tt,
             }
         }
 #ifdef _WIN32
-        if (rwflags & EVENT_READ)
+        if (!tt->wintun && (rwflags & EVENT_READ))
         {
             tun_read_queue(tt, 0);
         }