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Message-ID: <7850c4a6-2683-43f9-9d3b-6f4c164b2cb6@maxrnd.com>
Date: Tue, 22 Apr 2025 22:13:17 -0700
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Subject: Re: cygstart: buffer overflow when a URI is passed
 (cygutils-1.4.17-[23])
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From: Mark Geisert via Cygwin <cygwin AT cygwin DOT com>
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Hi Christian,

On 4/12/2025 9:37 AM, Christian Franke via Cygwin wrote:
> ggl329 via Cygwin wrote:
>> Hi all,
>>
>> I've encountered a possible bug in cygstart.
>> It seems to abort when a URI is passed to it.
>>
>>
>> $ cygcheck -dc | grep cygutils
>> cygutils                                1.4.17-3
>> $ cygstart https://www.google.com
>> *** buffer overflow detected ***: terminated
>> Aborted
> 
> Possibly no regression but longstanding bug which is now detected thanks 
> to gcc12's __builtin_dynamic_object_size() feature and -D_FORTIFY_SOURCE=3:
> 
> cygstart.c:
> 
> cygstart_mbs_to_wcs (const char *mbs_path, wchar_t **wcs_path)
> {
>    ...
>    *wcs_path = (wchar_t *) malloc ((len + 1) * sizeof (wchar_t));
>    ...
>    // *** buffer overflow detected *** because the length parameter
>    // should specify the number of characters instead of bytes:
>    if (mbstowcs (*wcs_path, mbs_path, (len + 1) * sizeof (wchar_t)) ...
>    ...
> }

It looks to me like that 'if' statement should read
   if (mbstowcs (*wcs_path, *mbs_path, len) ...
because 'len' determined near the top should be the number of characters 
involved, without a trailing NUL.  Then existing code fills in the NUL 
at character index 'len' in the buffer.  IOW the converted chars occupy 
character indexes 0 thru len-1.

If you concur I can update cygutils with this fix shortly.
Thanks & Regards,

..mark

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