From c18459e66e8e71a8765bb9b8e2b3d2ba61855a3f Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Tomasz=20Mo=C5=84?= <desowin@gmail.com>
Date: Thu, 16 Aug 2018 18:04:07 +0200
Subject: [PATCH] Fix extcap initialization deadlock

On Windows the code calling extcap worked as follows:
1. Create stdout and stderr pipes with default buffer size
2. Execute extcap redirecting output to the pipes
3. Wait for extcap process to exit
4. Read the data from stdout pipe

This resulted in deadlock when the extcap wrote more data than the pipe
could buffer. This was especially seen with USBPcap as it is quite
normal to have plenty of USB devices connected.

Fix the issue by contantly reading the stdout data and storing it in
GString. To prevent similar deadlock on the stderr, the stderr data is
being constantly monitored as well (and discarded).

Change-Id: I0f93e6d79617cef0e828aef2b96fad2757227923
Bug: 14657
Reviewed-on: https://code.wireshark.org/review/29159
Petri-Dish: Pascal Quantin <pascal.quantin@gmail.com>
Tested-by: Petri Dish Buildbot
Reviewed-by: Roland Knall <rknall@gmail.com>
---
 wsutil/ws_pipe.c | 78 ++++++++++++++++++++++++++++++++++++++++++++----
 1 file changed, 72 insertions(+), 6 deletions(-)

diff --git a/wsutil/ws_pipe.c b/wsutil/ws_pipe.c
index bd712bcb85..3deb3a0dbc 100644
--- a/wsutil/ws_pipe.c
+++ b/wsutil/ws_pipe.c
@@ -120,17 +120,83 @@ gboolean ws_pipe_spawn_sync(gchar *dirname, gchar *command, gint argc, gchar **a
 
     if (win32_create_process(NULL, winargs->str, NULL, NULL, TRUE, CREATE_NEW_CONSOLE, NULL, NULL, &info, &processInfo))
     {
-        gchar* buffer;
+        gchar* buffer = (gchar*)g_malloc(BUFFER_SIZE);
+        HANDLE handles[] = {processInfo.hProcess, child_stdout_rd, child_stderr_rd};
+        DWORD dw;
+        DWORD bytes_read;
+        DWORD bytes_avail;
+        GString *output_string = g_string_new(NULL);
 
-        WaitForSingleObject(processInfo.hProcess, INFINITE);
-        buffer = (gchar*)g_malloc(BUFFER_SIZE);
-        status = ws_read_string_from_pipe(child_stdout_rd, buffer, BUFFER_SIZE);
-        if (status)
+        for (;;)
         {
-            local_output = g_strdup_printf("%s", buffer);
+            dw = WaitForMultipleObjects(G_N_ELEMENTS(handles), handles, FALSE, INFINITE);
+            int idx = dw - WAIT_OBJECT_0;
+            if ((idx >= 0) && (idx < G_N_ELEMENTS(handles)))
+            {
+                if (handles[idx] == processInfo.hProcess)
+                {
+                    /* Process finished. Nothing left to do here. */
+                    break;
+                }
+                else if (handles[idx] == child_stdout_rd)
+                {
+                    if (PeekNamedPipe(child_stdout_rd, NULL, 0, NULL, &bytes_avail, NULL))
+                    {
+                        if (bytes_avail > 0)
+                        {
+                            bytes_avail = min(bytes_avail, BUFFER_SIZE);
+                            if (ReadFile(child_stdout_rd, &buffer[0], bytes_avail, &bytes_read, NULL))
+                            {
+                                g_string_append_len(output_string, buffer, bytes_read);
+                            }
+                        }
+                    }
+                }
+                else if (handles[idx] == child_stderr_rd)
+                {
+                    /* Discard the stderr data just like non-windows version of this function does. */
+                    if (PeekNamedPipe(child_stderr_rd, NULL, 0, NULL, &bytes_avail, NULL))
+                    {
+                        if (bytes_avail > 0)
+                        {
+                            bytes_avail = min(bytes_avail, BUFFER_SIZE);
+                            ReadFile(child_stderr_rd, &buffer[0], bytes_avail, &bytes_read, NULL);
+                        }
+                    }
+                }
+            }
+            else
+            {
+                g_log(LOG_DOMAIN_CAPTURE, G_LOG_LEVEL_DEBUG, "WaitForMultipleObjects returned 0x%08X. Error %d", dw, GetLastError());
+                break;
+            }
         }
+
+        /* At this point the process is finished but there might still be unread data in the pipe. */
+        while (PeekNamedPipe(child_stdout_rd, NULL, 0, NULL, &bytes_avail, NULL))
+        {
+            if (bytes_avail == 0)
+            {
+                /* Pipe is drained. */
+                break;
+            }
+            bytes_avail = min(bytes_avail, BUFFER_SIZE);
+            if (ReadFile(child_stdout_rd, &buffer[0], BUFFER_SIZE, &bytes_read, NULL))
+            {
+                g_string_append_len(output_string, buffer, bytes_read);
+            }
+        }
+
         g_free(buffer);
 
+        status = GetExitCodeProcess(processInfo.hProcess, &dw);
+        if (status && dw != 0)
+        {
+            status = FALSE;
+        }
+
+        local_output = g_string_free(output_string, FALSE);
+
         CloseHandle(child_stdout_rd);
         CloseHandle(child_stdout_wr);
         CloseHandle(child_stderr_rd);