strerror: Fix an error looking up some Windows error strings

- Use FORMAT_MESSAGE_IGNORE_INSERTS to ignore format specifiers in
  Windows error strings.

Since we are not in control of the error code we don't know what
information may be needed by the error string's format specifiers.

Prior to this change Windows API error strings which contain specifiers
(think specifiers like similar to printf specifiers) would not be shown.
The FormatMessage Windows API call which turns a Windows error code into
a string could fail and set error ERROR_INVALID_PARAMETER if that error
string contained a format specifier. FormatMessage expects a va_list for
the specifiers, unless inserts are ignored in which case no substitution
is attempted.

Ref: https://devblogs.microsoft.com/oldnewthing/20071128-00/?p=24353

1 files changed, 4 insertions, 2 deletions

diff --git a/lib/strerror.c b/lib/strerror.c
index d0650d80c..7aaa9f4a7 100644
--- a/lib/strerror.c
+++ b/lib/strerror.c
@@ -670,7 +670,8 @@ const char *Curl_strerror(int err, char *buf, size_t buflen)
     wchar_t wbuf[256];
     wbuf[0] = L'\0';
 
-    FormatMessage(FORMAT_MESSAGE_FROM_SYSTEM, NULL, err,
+    FormatMessage((FORMAT_MESSAGE_FROM_SYSTEM |
+                   FORMAT_MESSAGE_IGNORE_INSERTS), NULL, err,
                   LANG_NEUTRAL, wbuf, sizeof(wbuf)/sizeof(wchar_t), NULL);
     wcstombs(buf, wbuf, max);
   }
@@ -680,7 +681,8 @@ const char *Curl_strerror(int err, char *buf, size_t buflen)
     strncpy(buf, strerror(err), max);
   else {
     if(!get_winsock_error(err, buf, max) &&
-       !FormatMessageA(FORMAT_MESSAGE_FROM_SYSTEM, NULL, err,
+       !FormatMessageA((FORMAT_MESSAGE_FROM_SYSTEM |
+                        FORMAT_MESSAGE_IGNORE_INSERTS), NULL, err,
                        LANG_NEUTRAL, buf, (DWORD)max, NULL))
       msnprintf(buf, max, "Unknown error %d (%#x)", err, err);
   }