winspool: Correctly zero printer driver buffer on failure, with tests.

dlls/winspool.drv/info.c

@@ -4388,6 +4388,8 @@ BOOL WINAPI GetPrinterDriverW(HANDLE hPrinter, LPWSTR pEnvironment,
     TRACE("(%p,%s,%d,%p,%d,%p)\n",hPrinter,debugstr_w(pEnvironment),
 	  Level,pDriverInfo,cbBuf, pcbNeeded);
 
+    if (cbBuf > 0)
+        ZeroMemory(pDriverInfo, cbBuf);
 
     if (!(name = get_opened_printer_name(hPrinter))) {
         SetLastError(ERROR_INVALID_HANDLE);
@@ -4465,8 +4467,11 @@ BOOL WINAPI GetPrinterDriverA(HANDLE hPrinter, LPSTR pEnvironment,
     LPBYTE buf = NULL;
 
     if (cbBuf)
+    {
+        ZeroMemory(pDriverInfo, cbBuf);
         buf = HeapAlloc(GetProcessHeap(), 0, cbBuf);
-    
+    }
+
     pwstrEnvW = asciitounicode(&pEnvW, pEnvironment);
     ret = GetPrinterDriverW(hPrinter, pwstrEnvW, Level, buf,
 				    cbBuf, pcbNeeded);

dlls/winspool.drv/tests/info.c

@@ -2414,6 +2414,14 @@ static void test_GetPrinterDriver(void)
 
             /* XP allocates memory for both ANSI and unicode names */
             ok(filled >= calculated,"calculated %d != filled %d\n", calculated, filled);
+
+            /* Obscure test - demonstrate that Windows zero fills the buffer, even on failure */
+            if (di_2->pDataFile)
+            {
+                ret = GetPrinterDriver(hprn, NULL, level, buf, needed - 2, &filled);
+                ok(!ret, "level %d: GetPrinterDriver succeeded with less buffer than it should\n", level);
+                ok(di_2->pDataFile == NULL, "Even on failure, GetPrinterDriver clears the buffer to zeros\n");
+            }
         }
 
         HeapFree(GetProcessHeap(), 0, buf);