QWindowsPipeReader: fix possible invalid invocation of ReadFileEx()

If the user calls QLocalSocket::setReadBufferSize() with a value less
than the current size of the pipe buffer, startAsyncRead() would call
ReadFileEx() with invalid parameters:

  ReadFileEx(handle, nullptr, some_big_value, ...);

Change-Id: I3d153e3ec34f8038dc001c1c896aeceb666a8979
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>

1 files changed, 2 insertions, 2 deletions

diff --git a/src/corelib/io/qwindowspipereader.cpp b/src/corelib/io/qwindowspipereader.cpp
index b8df8e8084..827ed43b63 100644
--- a/src/corelib/io/qwindowspipereader.cpp
+++ b/src/corelib/io/qwindowspipereader.cpp
@@ -215,13 +215,13 @@ void QWindowsPipeReader::notified(DWORD errorCode, DWORD numberOfBytesRead)
 void QWindowsPipeReader::startAsyncRead()
 {
     const DWORD minReadBufferSize = 4096;
-    DWORD bytesToRead = qMax(checkPipeState(), minReadBufferSize);
+    qint64 bytesToRead = qMax(checkPipeState(), minReadBufferSize);
     if (pipeBroken)
         return;
 
     if (readBufferMaxSize && bytesToRead > (readBufferMaxSize - readBuffer.size())) {
         bytesToRead = readBufferMaxSize - readBuffer.size();
-        if (bytesToRead == 0) {
+        if (bytesToRead <= 0) {
             // Buffer is full. User must read data from the buffer
             // before we can read more from the pipe.
             return;