1 files changed, 16 insertions, 7 deletions
diff --git a/src/common/compat.c b/src/common/compat.c
index 334ea1b8b4..db2187b836 100644
--- a/src/common/compat.c
+++ b/src/common/compat.c
@@ -3046,28 +3046,37 @@ format_win32_error(DWORD err)
 {
   TCHAR *str = NULL;
   char *result;
+  DWORD n;
 
   /* Somebody once decided that this interface was better than strerror(). */
-  FormatMessage(FORMAT_MESSAGE_ALLOCATE_BUFFER |
+  n = FormatMessage(FORMAT_MESSAGE_ALLOCATE_BUFFER |
                  FORMAT_MESSAGE_FROM_SYSTEM |
                  FORMAT_MESSAGE_IGNORE_INSERTS,
                  NULL, err,
                  MAKELANGID(LANG_NEUTRAL, SUBLANG_DEFAULT),
-                (LPVOID)&str,
+                 (LPVOID)&str,
                  0, NULL);
 
-  if (str) {
+  if (str && n) {
 #ifdef UNICODE
-    char abuf[1024] = {0};
-    wcstombs(abuf,str,1024);
-    result = tor_strdup(abuf);
+    size_t len;
+    if (n > 128*1024)
+      len = (128 * 1024) * 2 + 1; /* This shouldn't be possible, but let's
+                                   * make sure. */
+    else
+      len = n * 2 + 1;
+    result = tor_malloc(len);
+    wcstombs(result,str,len);
+    result[len-1] = '\0';
 #else
     result = tor_strdup(str);
 #endif
-    LocalFree(str); /* LocalFree != free() */
   } else {
     result = tor_strdup("<unformattable error>");
   }
+  if (str) {
+    LocalFree(str); /* LocalFree != free() */
+  }
   return result;
 }
 #endif