Windows Pageant: option to open an AF_UNIX socket.

There's now a command-line option to make Pageant open an AF_UNIX
socket at a pathname of your choice. This allows it to act as an SSH
agent for any client program willing to use a WinSock AF_UNIX socket.

In particular, this allows WSL 1 processes to talk directly to Windows
Pageant without needing any intermediate process, because the AF_UNIX
sockets in the WSL 1 world interoperate with WinSock's ones.

(However, not WSL 2, which isn't very surprising.)

doc/pageant.but

@@ -217,6 +217,45 @@ point at a different program. You could point it at
 \cw{c:\\Windows\\System32\\OpenSSH\\ssh.exe} once you've done this
 setup \dash but it's just as easy to point it at Plink!
 
+\S{pageant-cmdline-unix} Unix-domain sockets: integrating with WSL 1
+
+Pageant can listen on the WinSock implementation of \q{Unix-domain
+sockets}. These interoperate with the Unix-domain sockets found in the
+original Windows Subsystem for Linux (now known as WSL 1). So if you
+ask Pageant to listen on one of these, then your WSL 1 processes can
+talk directly to Pageant.
+
+To configure this, run Pageant with the option \c{--unix}, followed
+with a pathname. Then, in WSL 1, set the environment variable
+\cw{SSH_AUTH_SOCK} to point at the WSL translation of that pathname.
+
+For example, you might run
+
+\c pageant --unix C:\Users\Simon\.ssh\agent.sock
+
+and in WSL 1, set the environment variable
+
+\c SSH_AUTH_SOCK=/mnt/c/Users/Simon/.ssh/agent.sock
+
+Alternatively, you can add a line to your \cw{.ssh/config} file inside
+WSL that says
+
+\c IdentityAgent /mnt/c/Users/Simon/.ssh/agent.sock
+
+although doing it like that may mean that \cw{ssh-add} commands won't
+find the agent, even though \cw{ssh} itself will.
+
+\s{Security note}: Unix-domain sockets are protected against access by
+other users by the file protections on their containing directory. So
+if your Windows machine is multiuser, make sure you create the socket
+inside a directory that other users can't access at all. (In fact,
+that's a good idea on general principles.)
+
+\s{Compatibility note}: WSL 2 processes cannot talk to Pageant by this
+mechanism, because WSL 2's Unix-domain sockets are managed by a
+separate Linux kernel, and not by the same kernel that WinSock talks
+to.
+
 \S{pageant-cmdline-keylist} Starting with the key list visible
 
 Start Pageant with the \i\c{--keylist} option to show the main window

windows/pageant.c

@@ -1391,6 +1391,7 @@ int WINAPI WinMain(HINSTANCE inst, HINSTANCE prev, LPSTR cmdline, int show)
 {
     MSG msg;
     const char *command = NULL;
+    const char *unixsocket = NULL;
     bool show_keylist_on_startup = false;
     int argc;
     char **argv, **argstart;
@@ -1494,6 +1495,8 @@ int WINAPI WinMain(HINSTANCE inst, HINSTANCE prev, LPSTR cmdline, int show)
             show_keylist_on_startup = true;
         } else if (match_optval("-openssh-config", "-openssh_config")) {
             openssh_config_file = val;
+        } else if (match_optval("-unix")) {
+            unixsocket = val;
         } else if (match_opt("-c")) {
             /*
              * If we see `-c', then the rest of the command line
@@ -1538,6 +1541,31 @@ int WINAPI WinMain(HINSTANCE inst, HINSTANCE prev, LPSTR cmdline, int show)
      * running, so set up all the machinery to answer requests.
      */
     if (!already_running) {
+        /*
+         * Set up the window class for the hidden window that receives
+         * all the messages to do with our presence in the system tray.
+         */
+
+        if (!prev) {
+            WNDCLASS wndclass;
+
+            memset(&wndclass, 0, sizeof(wndclass));
+            wndclass.lpfnWndProc = TrayWndProc;
+            wndclass.hInstance = inst;
+            wndclass.hIcon = LoadIcon(inst, MAKEINTRESOURCE(IDI_MAINICON));
+            wndclass.lpszClassName = TRAYCLASSNAME;
+
+            RegisterClass(&wndclass);
+        }
+
+        keylist = NULL;
+
+        traywindow = CreateWindow(TRAYCLASSNAME, TRAYWINTITLE,
+                                  WS_OVERLAPPEDWINDOW | WS_VSCROLL,
+                                  CW_USEDEFAULT, CW_USEDEFAULT,
+                                  100, 100, NULL, NULL, inst, NULL);
+        winselgui_set_hwnd(traywindow);
+
         /*
          * Initialise the cross-platform Pageant code.
          */
@@ -1546,9 +1574,10 @@ int WINAPI WinMain(HINSTANCE inst, HINSTANCE prev, LPSTR cmdline, int show)
         /*
          * Set up a named-pipe listener.
          */
-        Plug *pl_plug;
         wpc->plc.vt = &winpgnt_vtable;
         wpc->plc.suppress_logging = true;
+        {
+            Plug *pl_plug;
             struct pageant_listen_state *pl =
                 pageant_listener_new(&pl_plug, &wpc->plc);
             char *pipename = agent_named_pipe_name();
@@ -1569,9 +1598,10 @@ int WINAPI WinMain(HINSTANCE inst, HINSTANCE prev, LPSTR cmdline, int show)
             if (openssh_config_file) {
                 FILE *fp = fopen(openssh_config_file, "w");
                 if (!fp) {
-                char *err = dupprintf("Unable to write OpenSSH config file "
+                    char *err = dupprintf("Unable to write OpenSSH config "
-                                      "to %s", openssh_config_file);
+                                          "file to %s", openssh_config_file);
-                MessageBox(NULL, err, "Pageant Error", MB_ICONERROR | MB_OK);
+                    MessageBox(NULL, err, "Pageant Error",
+                               MB_ICONERROR | MB_OK);
                     return 1;
                 }
                 fprintf(fp, "IdentityAgent %s\n", pipename);
@@ -1579,6 +1609,31 @@ int WINAPI WinMain(HINSTANCE inst, HINSTANCE prev, LPSTR cmdline, int show)
             }
 
             sfree(pipename);
+        }
+
+        /*
+         * Set up an AF_UNIX listener too, if we were asked to.
+         */
+        if (unixsocket) {
+            sk_init();
+
+            /* FIXME: diagnose any error except file-not-found. Also,
+             * check the file type if possible? */
+            remove(unixsocket);
+
+            Plug *pl_plug;
+            struct pageant_listen_state *pl =
+                pageant_listener_new(&pl_plug, &wpc->plc);
+            Socket *sock = sk_newlistener_unix(unixsocket, pl_plug);
+            if (sk_socket_error(sock)) {
+                char *err = dupprintf("Unable to open AF_UNIX socket at %s "
+                                      "for SSH agent:\n%s", unixsocket,
+                                      sk_socket_error(sock));
+                MessageBox(NULL, err, "Pageant Error", MB_ICONERROR | MB_OK);
+                return 1;
+            }
+            pageant_listener_got_socket(pl, sock);
+        }
 
         /*
          * Set up the window class for the hidden window that receives
@@ -1661,31 +1716,6 @@ int WINAPI WinMain(HINSTANCE inst, HINSTANCE prev, LPSTR cmdline, int show)
         return 0;
     }
 
-    /*
-     * Set up the window class for the hidden window that receives
-     * all the messages to do with our presence in the system tray.
-     */
-
-    if (!prev) {
-        WNDCLASS wndclass;
-
-        memset(&wndclass, 0, sizeof(wndclass));
-        wndclass.lpfnWndProc = TrayWndProc;
-        wndclass.hInstance = inst;
-        wndclass.hIcon = LoadIcon(inst, MAKEINTRESOURCE(IDI_MAINICON));
-        wndclass.lpszClassName = TRAYCLASSNAME;
-
-        RegisterClass(&wndclass);
-    }
-
-    keylist = NULL;
-
-    traywindow = CreateWindow(TRAYCLASSNAME, TRAYWINTITLE,
-                              WS_OVERLAPPEDWINDOW | WS_VSCROLL,
-                              CW_USEDEFAULT, CW_USEDEFAULT,
-                              100, 100, NULL, NULL, inst, NULL);
-    winselgui_set_hwnd(traywindow);
-
     /* Set up a system tray icon */
     AddTrayIcon(traywindow);