A problem with noacl+umask+chmod result

[Andrey Repin]

Greetings, Orgad Shaneh!

> On Wed, Apr 7, 2021 at 11:47 PM Orgad Shaneh <orgads@gmail.com> wrote:
>>
>> Hi,
>>
>> If a filesystem is mounted with noacl, calling chmod to add write
>> permissions after umasking this permission doesn't work. Demonstrated
>> with command-line and C++.
>>
>> Did I miss something or is this a real bug? According to umask man, it
>> should only affect newly created files and directories, but I didn't
>> find anything that relates to chmod.
>>
>> Command-line:
>> touch foo
>> ls -l foo
>> # -rw-r--r-- ... foo
>> umask 200
>> chmod 0 foo
>> ls -l foo
>> # -r--r--r-- ... foo
>> chmod 200 foo
>> ls -l foo
>> # -r--r--r-- ... foo
>> # Expected to have rw

> Marco Atzeri replied to the mailing list but did not CC me, so I
> didn't receive it:

The expectation is that you subscribe to the list of interest.

>> without ACL you can not expect the POSIX scheme to properly work.
>> see
>> https://cygwin.com/cygwin-ug-net/ntsec.html
>> to understand how Cygwin uses ACL to mimic POSIX permissions

> Thanks Marco!

> I'm well aware of that. I don't expect it to work properly. From what
> I know, it can only set/unset user write bit. Read bits are always
> enabled, even on chmod 0.

> What I do expect is that the write bit will not be affected by umask.
> umask should only affect newly created files, not direct chmod
> commands.

Yet again: using chmod on noacl filesystem is likely to cause more harm than
good. You may very well end up with an unusable filesystem until you fix
permissions by hands.


-- 
With best regards,
Andrey Repin
Friday, April 9, 2021 4:43:01

Sorry for my terrible english...