oss-security - Re: Re: Trailing dot in Cygwin filenames [was: failed to clone iptables,ipset,nftables]

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Message-ID: <87sels7hhw.fsf@jacob.g10code.de>
Date: Mon, 28 Apr 2025 11:38:51 +0200
From: Werner Koch <wk@...pg.org>
To: Jan Engelhardt <ej@...i.de>
Cc: Florian Westphal <fw@...len.de>,  oss-security@...ts.openwall.com,
  Sunny73Cr <Sunny73Cr@...tonmail.com>,  "netfilter-devel@...r.kernel.org"
 <netfilter-devel@...r.kernel.org>
Subject: Re: Re: Trailing dot in Cygwin filenames [was:
 failed to clone iptables,ipset,nftables]

Hi!

> But Cygwin does something unusual, it *actually* creates a file with
> the 2-char sequence "y.", through whatever means. Explorer *shows* it

  C:\Users\dd9jn\test>echo foo >x.
  
  C:\Users\dd9jn\test>dir
  [...]
  28.04.2025  11:30                 6 x
                 1 Datei(en),              6 Bytes
  
  C:\Users\dd9jn\test>echo foo >\\?\\c:\users\dd9jn\test\x.
  
  C:\Users\dd9jn\test>dir
  [...]
  28.04.2025  11:30                 6 x
  28.04.2025  11:30                 6 x.
                 2 Datei(en),             12 Bytes
  
Thus you can create such a file using the Extended Path Length Prefix
which bypasses the mapping used by CreateFile.  For detailed info see
also

https://googleprojectzero.blogspot.com/2016/02/the-definitive-guide-on-win32-to-nt.html



Salam-Shalom,

   Werner

-- 
The pioneers of a warless world are the youth that
refuse military service.             - A. Einstein

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