Re: [ANNOUNCEMENT] Updated: Cygwin 1.7.35-1

[Achim Gratz <Stromeko at nexgo dot de>]

Thomas Wolff writes:
> This may happen on Linux as well. Just tested on a NAS runnig Debian,
> in a "share" partition:

In that case you've explicitly cleared the filemodes for the owner of
the file.  I'm talking about a case where the file access is purely
based on ACL, there are no ACL for the owner SID and Cygwin basically
creates those owner filemodes out of thin air.

>> So in that situation the group permissions need to be promoted to the owner permissions.
> I see no need to be more posixly here than other POSIX systems.

The owner modes are always explicitly set for POSIX systems and become
the u::+++, g::+++ and o::+++ base entries in the ACL.  The ACL check
algorithm gives these base entries absolute precedence over everything
else for compatibility with systems that don't have ACL, so if
euid==owner or egid==group no further entries in the ACL are ever
checked.

On Windows, the ACL are processed differently, which means that to do a
correct translation of Windows ACL into POSIX ACL Cygwin must compute
the base entries (and the filemodes) from the underlying full ACL,
otherwise the apparent (via POSIX applications) and the effective (via
Windows) access rights become different.  And yes, that means that in
some situations the POSIX file modes can change when the Windows ACL are
changing, while this is not possible on POSIX systems.


Regards,
Achim.
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