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To:	cygwin AT cygwin DOT com
From:	Achim Gratz <Stromeko AT NexGo DOT DE>
Subject:	Shares with strange ACL settings
Date:	Tue, 11 Aug 2015 08:42:10 +0000 (UTC)
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I've thought some more about those strange shares I need to use that have
inherited ACL that don't let me change the ACL at all and hence prevent
Cygwin from fixing up the POSIX permissions.  That generally ends up with
permissions like these:

% ll test
total 10
d---rwx---+ 1 gratz          Domain Users    0 Aug 10 11:51 ./
d---rwx---+ 1 Administrators Administrators  0 Aug 10 11:50 ../
----rwx---+ 1 gratz          Domain Users   18 Aug 10 11:51 blafasel*
----rwx---+ 1 gratz          Domain Users   18 Aug 10 11:51 blumblum*

Some applications that know how POSIX ACL are supposed to work conclude that
such directories or files are not readable:

% cd test
% perl -E 'say -r "." ? "readable" : "not readable";'
not readable
% perl -E 'say -r "blafasel" ? "readable" : "not readable";'
not readable

Other applications not using this shortcut and going all the way to
faccessat correctly determine readability:

% [ -r . ] && echo readable || echo not readable
readable
(1056)/mnt/upload/test > [ -r blafasel ] && echo readable || echo not readable
readable

If I access the files from another account (that has the same group
memberships that give read/write access to the share) or change the owner,
then the shortcut is never invoked:

$ perl -E 'say -r "." ? "readable" : "not readable";'
readable
$ perl -E 'say -r "blafasel" ? "readable" : "not readable";'
readable
$ [ -r . ] && echo readable || echo not readable
readable
$ [ -r blafasel ] && echo readable || echo not readable
readable

So, it would probably help if I had a mount option to force the ownership to
some account that I am never logged in as, either via a mount option or
whenever the POSIX user modes are all cleared.  I don't know if that might
confuse applications when they check ownership on newly created files,
though.  Is that something that is implementable easily so it could be
tested via a snapshot?


Regards,
Achim.



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