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Date:	Fri, 28 Aug 2009 12:06:24 +0200
Reply-To:	"Christian Franke" <Christian DOT Franke AT t-online DOT de>
To:	"Cygwin" <cygwin AT cygwin DOT com>
Subject:	=?ISO-8859-15?Q?=5B1.7=5D_Admins_can_write_to_readonly_files?=
From:	"Christian Franke" <Christian DOT Franke AT t-online DOT de>
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For members of Admin group, Cygwin 1.7 allows to overwrite files without
write permission, but Cygwin 1.5 does not.

Is this a intended change of 1.7 ?

I would suggest to add a note to
http://cygwin.com/1.7/cygwin-ug-net/ov-new1.7.html


Testcase (WinXP SP2 and 3, Cygwin 1.7.0-60):

$ touch foo

$ chmod a=r foo

$ ls -l foo
-r--r--r-- 1 franke none 0 Aug 28 11:17 foo

$ cacls foo | grep FILE_WRITE_DATA

$ attrib foo
A          C:\cygwin\tmp\foo

$ dd if=/dev/zero bs=1 count=1 of=foo
1+0 records in
1+0 records out
1 byte (1 B) copied, 0 s, Infinity B/s


Same file, but Cygwin 1.5:

$ dd if=/dev/zero bs=1 count=1 of=foo
dd: opening `foo': Permission denied


fhandler_base::open() calls NtCreateFile() with different
'creation_options' values:

1.5.0-25:
0x0420 = FILE_OPEN_FOR_RECOVERY|FILE_SYNCHRONOUS_IO_NONALERT

1.7.0-60:
0x4020 = FILE_OPEN_FOR_BACKUP_INTENT|FILE_SYNCHRONOUS_IO_NONALERT

What is the effect of FILE_OPEN_FOR_RECOVERY ?

-- 
Regards
Christian Franke




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