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From: Werner Koch <wk@gnupg.org>
To: Jan Engelhardt <ej@inai.de>
Cc: Florian Westphal <fw@strlen.de>,
	 oss-security@lists.openwall.com,
	Sunny73Cr <Sunny73Cr@protonmail.com>,
	 "netfilter-devel@vger.kernel.org"
	<netfilter-devel@vger.kernel.org>
Subject: Re: [oss-security] Re: Trailing dot in Cygwin filenames [was: failed to clone iptables,ipset,nftables]
Date: Mon, 28 Apr 2025 11:38:51 +0200	[thread overview]
Message-ID: <87sels7hhw.fsf@jacob.g10code.de> (raw)
In-Reply-To: <sqo7nqpr-151q-4sr4-1o40-r95r62179s29@vanv.qr> (Jan Engelhardt's message of "Fri, 25 Apr 2025 09:46:15 +0200 (CEST)")

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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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  reply	other threads:[~2025-04-28 10:17 UTC|newest]

Thread overview: 5+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2025-04-25  5:30 Fail to clone iptables,ipset,nftables Sunny73Cr
2025-04-25  6:22 ` Florian Westphal
2025-04-25  7:46   ` Trailing dot in Cygwin filenames [was: failed to clone iptables,ipset,nftables] Jan Engelhardt
2025-04-28  9:38     ` Werner Koch [this message]
2025-04-25 11:17   ` Fail to clone iptables,ipset,nftables Sunny73Cr

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