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cygwin wcsxfrm: byte swap result ourselves

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Workaround a bug (or undocumented behaviour) in LCMapStringW:

It's documented(*) that the cchDest parameter is a byte count with
LCMAP_SORTKEY, but a character count otherwise.  But the docs don't
state what happens if you combine LCMAP_SORTKEY with LCMAP_BYTEREV.

Tests indicate that LCMAP_SORTKEY treats cchDest as byte count, but
then LCMAP_BYTEREV treats it as char count in the same call.  So the
latter swaps twice as much bytes in the destination buffer than the
byte count it returns, which potentially results in writing past the
end of the given output buffer.

Solution: Don't specify LCMAP_BYTEREV in the LCMapStringW(LCMAP_SORTKEY)
call, rather byte swap afterwards.

(*) https://msdn.microsoft.com/en-us/library/windows/desktop/dd318702(v=vs.85).aspx

Signed-off-by: Corinna Vinschen <corinna@vinschen.de>
This commit is contained in:
Corinna Vinschen 2017-06-06 18:27:47 +02:00
parent 780503f6ac
commit c0d7d3e1a2
1 changed files with 13 additions and 8 deletions
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21
winsup/cygwin/nlsfuncs.cc
View File

@ -1196,15 +1196,21 @@ wcsxfrm_l (wchar_t *__restrict ws1, const wchar_t *__restrict ws2, size_t wsn,
if (!collate_lcid)
return wcslcpy (ws1, ws2, wsn);
ret = LCMapStringW (collate_lcid, LCMAP_SORTKEY | LCMAP_BYTEREV,
ws2, -1, ws1, wsn * sizeof (wchar_t));
/* LCMapStringW returns byte count including the terminating NUL character,
wcsxfrm is supposed to return length in wchar_t excluding the NUL.
Since the array is only single byte NUL-terminated we must make sure
the result is wchar_t-NUL terminated. */
/* Don't use LCMAP_SORTKEY in conjunction with LCMAP_BYTEREV. The cchDest
parameter is used as byte count with LCMAP_SORTKEY but as char count with
LCMAP_BYTEREV. */
ret = LCMapStringW (collate_lcid, LCMAP_SORTKEY, ws2, -1, ws1,
wsn * sizeof (wchar_t));
if (ret)
{
ret /= sizeof (wchar_t);
/* Byte swap the array ourselves here. */
for (size_t idx = 0; idx < ret; ++idx)
ws1[idx] = __builtin_bswap16 (ws1[idx]);
/* LCMapStringW returns byte count including the terminating NUL char.
wcsxfrm is supposed to return length in wchar_t excluding the NUL.
Since the array is only single byte NUL-terminated yet, make sure
the result is wchar_t-NUL terminated. */
if (ret < wsn)
ws1[ret] = L'\0';
return ret;
@ -1213,8 +1219,7 @@ wcsxfrm_l (wchar_t *__restrict ws1, const wchar_t *__restrict ws2, size_t wsn,
set_errno (EINVAL);
else
{
ret = LCMapStringW (collate_lcid, LCMAP_SORTKEY | LCMAP_BYTEREV, ws2, -1,
NULL, 0);
ret = LCMapStringW (collate_lcid, LCMAP_SORTKEY, ws2, -1, NULL, 0);
if (ret)
wsn = ret / sizeof (wchar_t);
}