TEST RELEASE: Cygwin 2.4.0-0.9
Mon Dec 7 15:57:00 GMT 2015
Hi Cygwin friends and users,
I released TEST version 2.4.0-0.9 of Cygwin.
- This version patches the Windows 10 1511 workaround added to
2.4.0-0.7. Cygwin now always uses a self-created main thread stack
in a memory area with very low probability of collision with the OS.
The fix addresses the problem reported in
Due to the imminent holiday schedule, I postponed the official release
of Cygwin 2.4.0 to early 2016.
Testing is still highly appreciated...
This is the "new POSIX ACL handling reloaded" release.
In local testing I successfully integrated AuthZ into the current Cygwin
code to generate more correct user permissions by being able to generate
effective permissions for arbitrary users.
This success convinced me that it might be possible to pick up the POSIX
permission rewrite originally targeted for the 2.0.0 release and try to
update it using AuthZ and generally revamp it to reflect effective
My local testing looks good, but this is a major change, so this code
really needs a lot more testing in various scenarios. Especially
some Windows ACLs created in corporate environments are often a hard
nut to crack, and the example from
which was the ultimate downfall of the original implementation is
the stuff which needs some good testing.
There's, as usual, a downside: AuthZ leans a bit to the slow side.
Cygwin caches information already gathered once on a per-process basis,
but in locally crafted worst case scenarios (`ls' on lots of file owned
by lots of different users and groups) the slowdown may be up to 25%.
But that's really just a worst case, in the usual scenarios the slowdown
should be mostly unnoticable.
To alleviate the problem, the AuthZ code is fortunately only called for
non-Cygwin ACLs and Cygwin ACLs created before this release. Within a
pure Cygwin environment (e.g., some build directory only used with
Cygwin tools) AuthZ should be practically unused.
Apart from the aforementioned code changes to "just do it right", there
are two additional changes I implemented for this new POSIX ACL revamp
- I reverted the questionable change I added to 2.0.0-0.7 in terms of
chmod group permission handling. The original description of this
If you have a non-trivial ACL with secondary accounts and thus a
mask value, chmod is supposed to change only the mask, not the
permissions of the primary group. However, if the primary group has
few permissions to begin with, the result is really surprising. ls
-l would, e.g., show read/write perms for the group, but the group
might still have only read perms.
Personally I find this chmod behaviour really, really bad, so I took
the liberty to change it in a way which gives a much less surprising
result: If you call chmod on a non-trivial ACL, the group
permissions will be used for the primary group and the mask.
- setfacl(1) now accepts the combination of the -b and -k options, just as
As for the description what this implementation strives for, please see
- New, unified implementation of POSIX permission and ACL handling. The
new ACLs now store the POSIX ACL MASK/CLASS_OBJ permission mask, and
they allow to inherit the S_ISGID bit. ACL inheritance now really
works as desired, in a limited, but theoretically equivalent fashion
even for non-Cygwin processes.
To accommodate standard Windows ACLs, the POSIX permissions of the
owner and all other users in the ACL are computed using the Windows
AuthZ API. This may slow down the computation of POSIX permissions
noticably in some circumstances, but is generally more correct. The
new code also ignores SYSTEM and Administrators group permissions when
computing the MASK/CLASS_OBJ permission mask on old ACLs, and it
doesn't deny access to SYSTEM and Administrators group based on the
value of MASK/CLASS_OBJ when creating the new ACLs.
The new code now handles the S_ISGID bit on directories as on Linux:
Setting S_ISGID on a directory causes new files and subdirs created
within to inherit its group, rather than the primary group of the user
who created the file. This only works for files and directories
created by Cygwin processes.
- New API: rpmatch.
- setfacl(1) now allows to use the -b and -k option combined to allow reducing
an ACL to only reflect standard POSIX permissions.
- Fix (numeric and monetary) decimal point and thousands separator in
fa_IR and ps_AF locales to be aligned with Linux.
- Not a bug fix as such, but a workaround for new behaviour in Windows 10
version 1511 64 bit. This version introduces a problem which existed in
a similar variation (just vice versa) in XP and Server 2003 64 bit as well.
An unexpected stack arrangement when starting a 64 bit Cygwin application
from a 32 bit application (e.g. 32 bit CMD.EXE) broke Cygwin's fork.
- Replaced old, buggy strtold implementation with well-tested gdtoa version
from David M. Gay.
- Fix handling of relative paths in native symlinks if the target is in a
drive's root dir or one level below.
- Fix a SEGV when calling `kill -l 0'.
- Fix a race condition in signal handling.
Corinna Vinschen Please, send mails regarding Cygwin to
Cygwin Maintainer cygwin AT cygwin DOT com
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