Enable dhcp on tap adapter using interactive service

Currently, if dhcp on the TAP interface is disabled, OpenVPN
on Windows tries to enable it using netsh but that succeeds only when
run with admin privileges.

When interactive service is available, delegate this task to the
service.

Trac: #1111
Tested on Windows 7

Signed-off-by: Selva Nair <selva.nair@gmail.com>
Acked-by: Lev Stipakov <lstipakov@gmail.com>
Acked-by: Gert Doering <gert@greenie.muc.de>
Message-Id: <1538510474-27602-2-git-send-email-selva.nair@gmail.com>
URL: https://www.mail-archive.com/openvpn-devel@lists.sourceforge.net/msg17517.html
Signed-off-by: Gert Doering <gert@greenie.muc.de>
(cherry picked from commit b4fc8bbd6b1d0211dd6982c4accedfbe4ae7e3ed)

diff --git a/include/openvpn-msg.h b/include/openvpn-msg.h
index 82ecfe8bddcca9b513a4a6b3755aee7806623069..66177a21fdfd374b1941101f6354b06b156d30d0 100644 (file)
--- a/include/openvpn-msg.h
+++ b/include/openvpn-msg.h
@@ -37,7 +37,8 @@ typedef enum {
     msg_flush_neighbors,
     msg_add_block_dns,
     msg_del_block_dns,
-    msg_register_dns
+    msg_register_dns,
+    msg_enable_dhcp,
 } message_type_t;
 
 typedef struct {
@@ -111,4 +112,9 @@ typedef struct {
     interface_t iface;
 } block_dns_message_t;
 
+typedef struct {
+    message_header_t header;
+    interface_t iface;
+} enable_dhcp_message_t;
+
 #endif /* ifndef OPENVPN_MSG_H_ */

diff --git a/src/openvpn/tun.c b/src/openvpn/tun.c
index db7c25ff5a5f99dbd4ccfe5ba5a6716ee9d744ee..91e73a89d7f8ca26c759abc5f1361e395cf81ae1 100644 (file)
--- a/src/openvpn/tun.c
+++ b/src/openvpn/tun.c
@@ -5371,6 +5371,49 @@ netsh_enable_dhcp(const struct tuntap_options *to,
     argv_reset(&argv);
 }
 
+/* Enable dhcp on tap adapter using iservice */
+static bool
+service_enable_dhcp(const struct tuntap *tt)
+{
+    DWORD len;
+    bool ret = false;
+    ack_message_t ack;
+    struct gc_arena gc = gc_new();
+    HANDLE pipe = tt->options.msg_channel;
+
+    enable_dhcp_message_t dhcp = {
+        .header = {
+            msg_enable_dhcp,
+            sizeof(enable_dhcp_message_t),
+            0
+        },
+        .iface = { .index = tt->adapter_index, .name = "" }
+    };
+
+    if (!WriteFile(pipe, &dhcp, sizeof(dhcp), &len, NULL)
+        || !ReadFile(pipe, &ack, sizeof(ack), &len, NULL))
+    {
+        msg(M_WARN, "Enable_dhcp: could not talk to service: %s [%lu]",
+            strerror_win32(GetLastError(), &gc), GetLastError());
+        goto out;
+    }
+
+    if (ack.error_number != NO_ERROR)
+    {
+        msg(M_NONFATAL, "TUN: enabling dhcp using service failed: %s [status=%u if_index=%d]",
+            strerror_win32(ack.error_number, &gc), ack.error_number, dhcp.iface.index);
+    }
+    else
+    {
+        msg(M_INFO, "DHCP enabled on interface %d using service", dhcp.iface.index);
+        ret = true;
+    }
+
+out:
+    gc_free(&gc);
+    return ret;
+}
+
 /*
  * Return a TAP name for netsh commands.
  */
@@ -5851,7 +5894,15 @@ open_tun(const char *dev, const char *dev_type, const char *dev_node, struct tun
              */
             if (dhcp_status(tt->adapter_index) == DHCP_STATUS_DISABLED)
             {
-                netsh_enable_dhcp(&tt->options, tt->actual_name);
+                /* try using the service if available, else directly execute netsh */
+                if (tt->options.msg_channel)
+                {
+                    service_enable_dhcp(tt);
+                }
+                else
+                {
+                    netsh_enable_dhcp(&tt->options, tt->actual_name);
+                }
             }
             dhcp_masq = true;
             dhcp_masq_post = true;

diff --git a/src/openvpnserv/interactive.c b/src/openvpnserv/interactive.c
index 5ba91d77709bd8e38f06e437e57c351f386e616e..c4898cbe69ba143d69cf869d4d0c1396946e914b 100644 (file)
--- a/src/openvpnserv/interactive.c
+++ b/src/openvpnserv/interactive.c
@@ -1165,6 +1165,45 @@ out:
     return err;
 }
 
+static DWORD
+HandleEnableDHCPMessage(const enable_dhcp_message_t *dhcp)
+{
+    DWORD err = 0;
+    DWORD timeout = 5000; /* in milli seconds */
+    wchar_t argv0[MAX_PATH];
+
+    /* Path of netsh */
+    swprintf(argv0, _countof(argv0), L"%s\\%s", get_win_sys_path(), L"netsh.exe");
+    argv0[_countof(argv0) - 1] = L'\0';
+
+    /* cmd template:
+     * netsh interface ipv4 set address name=$if_index source=dhcp
+     */
+    const wchar_t *fmt = L"netsh interface ipv4 set address name=\"%d\" source=dhcp";
+
+    /* max cmdline length in wchars -- include room for if index:
+     * 10 chars for 32 bit int in decimal and +1 for NUL
+     */
+    size_t ncmdline = wcslen(fmt) + 10 + 1;
+    wchar_t *cmdline = malloc(ncmdline*sizeof(wchar_t));
+    if (!cmdline)
+    {
+        err = ERROR_OUTOFMEMORY;
+        return err;
+    }
+
+    openvpn_sntprintf(cmdline, ncmdline, fmt, dhcp->iface.index);
+
+    err = ExecCommand(argv0, cmdline, timeout);
+
+    /* Note: This could fail if dhcp is already enabled, so the caller
+     * may not want to treat errors as FATAL.
+     */
+
+    free(cmdline);
+    return err;
+}
+
 static VOID
 HandleMessage(HANDLE pipe, DWORD bytes, DWORD count, LPHANDLE events, undo_lists_t *lists)
 {
@@ -1176,6 +1215,7 @@ HandleMessage(HANDLE pipe, DWORD bytes, DWORD count, LPHANDLE events, undo_lists
         flush_neighbors_message_t flush_neighbors;
         block_dns_message_t block_dns;
         dns_cfg_message_t dns;
+        enable_dhcp_message_t dhcp;
     } msg;
     ack_message_t ack = {
         .header = {
@@ -1236,6 +1276,13 @@ HandleMessage(HANDLE pipe, DWORD bytes, DWORD count, LPHANDLE events, undo_lists
             ack.error_number = HandleDNSConfigMessage(&msg.dns, lists);
             break;
 
+        case msg_enable_dhcp:
+            if (msg.header.size == sizeof(msg.dhcp))
+            {
+                ack.error_number = HandleEnableDHCPMessage(&msg.dhcp);
+            }
+            break;
+
         default:
             ack.error_number = ERROR_MESSAGE_TYPE;
             MsgToEventLog(MSG_FLAGS_ERROR, TEXT("Unknown message type %d"), msg.header.type);