DMARC-Filter: OpenDMARC Filter v1.4.2 sourceware.org 584E23858D20
Subject: readdir() returns inaccessible name if file was created with invalid
 UTF-8
To: cygwin AT cygwin DOT com
Message-ID: <96f2253b-791b-b8a0-97dd-8d257eefb9b1@t-online.de>
Date: Sun, 15 Sep 2024 19:47:11 +0200
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From: Christian Franke via Cygwin <cygwin AT cygwin DOT com>
Reply-To: Christian Franke <Christian DOT Franke AT t-online DOT de>
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Sender: "Cygwin" <cygwin-bounces~archive-cygwin=delorie DOT com AT cygwin DOT com>
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If a file name contains an invalid (truncated) UTF-8 sequence, open() 
does not refuse to create the file. Later readdir() returns a different 
name which could not be used to access the file.

Testcase with U+1F321 (Thermometer):

$ uname -r
3.5.4-1.x86_64

$ printf $'\U0001F321' | od -A none -t x1
  f0 9f 8c a1

$ touch 'file1-'$'\xf0\x9f\x8c\xa1''.ext'

$ touch 'file2-'$'\xf0\x9f\x8c''.ext'

$ touch 'file3-'$'\xf0\x9f\x8c'

$ ls -1
ls: cannot access 'file2-.?ext': No such file or directory
ls: cannot access 'file3-': No such file or directory
'file1-'$'\360\237\214\241''.ext'
file2-.?ext
file3-


Name mapping according to "fhandler_disk_file::readdir" strace lines:

"file1-\xF0\x9F\x8C\xA1.ext" -(open)-> L"file1-\xD83C\xDF21.ext" 
-(readdir)->
"file1-\xF0\x9F\x8C\xA1.ext"

"file2-\xF0\x9f\x8C.ext" -(open)-> L"file2-\xD83C\xF02Eext" -(readdir)->
"file2-.\xE1\x9E\xB3ext"

"file3-\xF0\x9F\x8C" -(open)-> L"file3-\xD83C\xF000" -(readdir)->
"file3-"

Issue found because 'stress-ng --filename ...' could not cleanup its 
temp directory.

-- 
Regards,
Christian


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