agent: Add support for Windows OpenSSH agent

The implementation was taken and modified from that found in the
Portable OpenSSH port to Win32 by the PowerShell team.

https://github.com/PowerShell/openssh-portable

COPYING

@@ -4,6 +4,8 @@
  * Copyright (c) 2007 Eli Fant <elifantu@mail.ru>
  * Copyright (c) 2009-2019 Daniel Stenberg
  * Copyright (C) 2008, 2009 Simon Josefsson
+ * Copyright (c) 2000 Markus Friedl
+ * Copyright (c) 2015 Microsoft Corp.
  * All rights reserved.
  *
  * Redistribution and use in source and binary forms,

src/agent.c

@@ -50,6 +50,9 @@
 #endif
 #include "userauth.h"
 #include "session.h"
+#ifdef WIN32
+#include <stdlib.h>
+#endif
 
 /* Requests from client to agent for protocol 1 key operations */
 #define SSH_AGENTC_REQUEST_RSA_IDENTITIES 1
@@ -362,6 +365,220 @@ struct agent_ops agent_ops_pageant = {
     agent_transact_pageant,
     agent_disconnect_pageant
 };
+
+/* Code to talk to OpenSSH was taken from Win32 port of Portable OpenSSH by the
+ * PowerShell team.
+ *
+ * Author: Tatu Ylonen <ylo@cs.hut.fi>
+ * Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland
+ *                    All rights reserved
+ * Functions for connecting the local authentication agent.
+ *
+ * As far as I am concerned, the code I have written for this software
+ * can be used freely for any purpose.  Any derived versions of this
+ * software must be clearly marked as such, and if the derived work is
+ * incompatible with the protocol description in the RFC file, it must be
+ * called by a name other than "ssh" or "Secure Shell".
+ *
+ * SSH2 implementation,
+ * Copyright (c) 2000 Markus Friedl.  All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ * 1. Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in the
+ *    documentation and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
+ * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
+ * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
+ * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
+ * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
+ * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+ * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+ * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+ * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
+ * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ *
+ * Copyright (c) 2015 Microsoft Corp.
+ * All rights reserved
+ *
+ * Microsoft openssh win32 port
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright
+ * notice, this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ * notice, this list of conditions and the following disclaimer in the
+ * documentation and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
+ * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
+ * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
+ * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
+ * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
+ * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+ * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+ * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+ * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
+ * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#define WIN32_OPENSSH_AGENT_SOCK "\\\\.\\pipe\\openssh-ssh-agent"
+
+static HANDLE win32_openssh_socket_handle = INVALID_HANDLE_VALUE;
+
+static int
+agent_connect_openssh(LIBSSH2_AGENT *agent)
+{
+    int ret = LIBSSH2_ERROR_NONE;
+    const char *path;
+    HANDLE h = INVALID_HANDLE_VALUE;
+
+    path = agent->identity_agent_path;
+    if(!path) {
+        path = getenv("SSH_AUTH_SOCK");
+        if(!path)
+            path = WIN32_OPENSSH_AGENT_SOCK;
+    }
+
+    while(1) {
+        h = CreateFileA(
+            path,
+            GENERIC_READ | GENERIC_WRITE,
+            0,
+            NULL,
+            OPEN_EXISTING,
+            /* FILE_FLAG_OVERLAPPED | */
+            SECURITY_SQOS_PRESENT |
+            SECURITY_IDENTIFICATION,
+            NULL
+        );
+
+        if(h != INVALID_HANDLE_VALUE)
+            break;
+        if(GetLastError() != ERROR_PIPE_BUSY)
+            break;
+
+        /* Wait up to 1 second for a pipe instance to become available */
+        if(!WaitNamedPipeA(path, 1000))
+            break;
+    }
+
+    if(h == INVALID_HANDLE_VALUE) {
+        ret = _libssh2_error(agent->session, LIBSSH2_ERROR_AGENT_PROTOCOL,
+                             "unable to connect to agent pipe");
+        goto cleanup;
+    }
+
+    if(SetHandleInformation(h, HANDLE_FLAG_INHERIT, 0) == FALSE) {
+        ret = _libssh2_error(agent->session, LIBSSH2_ERROR_AGENT_PROTOCOL,
+                             "unable to set handle information of agent pipe");
+        goto cleanup;
+    }
+
+    win32_openssh_socket_handle = h;
+    h = INVALID_HANDLE_VALUE;
+    agent->fd = 0; /* Mark as the connection has been established */
+
+cleanup:
+    if(h != INVALID_HANDLE_VALUE)
+        CloseHandle(h);
+    return ret;
+}
+
+/* TODO: async operations */
+static int
+agent_transact_openssh(LIBSSH2_AGENT *agent, agent_transaction_ctx_t transctx)
+{
+    unsigned char buf[4];
+
+    /* Send the length of the request */
+    if(transctx->state == agent_NB_state_request_created) {
+        _libssh2_htonu32(buf, transctx->request_len);
+        if(!WriteFile(win32_openssh_socket_handle, buf, 4, NULL, NULL)) {
+            if(ERROR_IO_PENDING == GetLastError())
+                return LIBSSH2_ERROR_EAGAIN;
+
+            return _libssh2_error(agent->session, LIBSSH2_ERROR_SOCKET_SEND,
+                                      "agent send failed");
+        }
+        transctx->state = agent_NB_state_request_length_sent;
+    }
+
+    /* Send the request body */
+    if(transctx->state == agent_NB_state_request_length_sent) {
+        if(!WriteFile(win32_openssh_socket_handle, transctx->request,
+                      transctx->request_len, NULL, NULL)) {
+            if(ERROR_IO_PENDING == GetLastError())
+                return LIBSSH2_ERROR_EAGAIN;
+
+            return _libssh2_error(agent->session, LIBSSH2_ERROR_SOCKET_SEND,
+                                      "agent send failed");
+        }
+        transctx->state = agent_NB_state_request_sent;
+    }
+
+    /* Receive the length of the body */
+    if(transctx->state == agent_NB_state_request_sent) {
+        if(!ReadFile(win32_openssh_socket_handle, buf, 4, NULL, NULL)) {
+            if(ERROR_IO_PENDING == GetLastError())
+                return LIBSSH2_ERROR_EAGAIN;
+
+            return _libssh2_error(agent->session, LIBSSH2_ERROR_SOCKET_RECV,
+                                  "agent recv failed");
+        }
+        transctx->response_len = _libssh2_ntohu32(buf);
+        transctx->response = LIBSSH2_ALLOC(agent->session,
+                                           transctx->response_len);
+        if(!transctx->response)
+            return LIBSSH2_ERROR_ALLOC;
+
+        transctx->state = agent_NB_state_response_length_received;
+    }
+
+    /* Receive the response body */
+    if(transctx->state == agent_NB_state_response_length_received) {
+        if(!ReadFile(win32_openssh_socket_handle, transctx->response,
+                     transctx->response_len, NULL, NULL)) {
+            if(ERROR_IO_PENDING == GetLastError())
+                return LIBSSH2_ERROR_EAGAIN;
+
+            return _libssh2_error(agent->session, LIBSSH2_ERROR_SOCKET_RECV,
+                                  "agent recv failed");
+        }
+        transctx->state = agent_NB_state_response_received;
+    }
+
+    return LIBSSH2_ERROR_NONE;
+}
+
+static int
+agent_disconnect_openssh(LIBSSH2_AGENT *agent)
+{
+    if(!CancelIo(win32_openssh_socket_handle))
+        return _libssh2_error(agent->session, LIBSSH2_ERROR_SOCKET_DISCONNECT,
+                              "failed to cancel pending IO of agent pipe");
+    /* let queued APCs (if any) drain */
+    SleepEx(0, TRUE);
+    if(!CloseHandle(win32_openssh_socket_handle))
+        return _libssh2_error(agent->session, LIBSSH2_ERROR_SOCKET_DISCONNECT,
+                              "failed to close handle to agent pipe");
+
+    return LIBSSH2_ERROR_NONE;
+}
+
+struct agent_ops agent_ops_openssh = {
+    agent_connect_openssh,
+    agent_transact_openssh,
+    agent_disconnect_openssh
+};
 #endif  /* WIN32 */
 
 static struct {
@@ -370,6 +587,7 @@ static struct {
 } supported_backends[] = {
 #ifdef WIN32
     {"Pageant", &agent_ops_pageant},
+    {"OpenSSH", &agent_ops_openssh},
 #endif  /* WIN32 */
 #ifdef PF_UNIX
     {"Unix", &agent_ops_unix},