setup/mkpasswd and HOMEDRIVE/HOMEPATH

Corinna Vinschen corinna-cygwin@cygwin.com
Thu May 7 10:18:00 GMT 2009


On May  7 00:44, Larry Hall (Cygwin Developers) wrote:
> Dave Korn wrote:
>> Larry Hall (Cygwin Developers) wrote:
>>> I was basically thinking of the pathelogical case where the user
>>> doesn't have permissions to create or access the home directory
>>> due to some strange phenomena (somebody messed up permissions,
>>> '/home/<user>' points to a shared drive that's inaccessible, etc.).
>>
>>   I was thinking of that too, but I'd hardly call it 'pathological'.  It's
>> standard practice on Linux for /home to be owned by root and only have r-x
>> perms for everyone else, as root is the only one who should be adding new
>> users and hence the only person who should be creating dirs in /home.
>>
>>   In cygwin we're effectively letting non-admin users control most of the
>> 'adduser' behaviour themselves.  Someone might easily think that chmod'ing
>> /home 755 was a good idea.
>
> Right.
>
> And as to the terminology, let's call them "corner cases" instead so no one
> gets hung up on semantics. :-)

But how's that supposed to work?  Right now (and also in the former
code) Cygwin doesn't (and didn't) check for any directory permissions.
Evaluating the home directory is just a question of where to get the
information from

  $HOME
  /etc/passwd
  ($HOMEDIRVE/$HOMEPATH)
  default /home/$USER or /.

As for /home permissions, the old setup together with the old Cygwin
(<= 1.7.0-46) created /home with 777 permissions.  Actually setup didn't
create /home at all, /etc/profile did, and umask was set to 0000 in Cygwin
by default.  And /etc/profile creates /home before setting umask.  So
777 was the typical outcome so far, unfortunately not only for /home,
but also for the /home/$USER.

The new combination of setup-1.7 and Cygwin 1.7.0-47 will do it
different.  Setup now actually creates /home right at the start with
1777 permissions.  And Cygwin has a default umask of 022.  So the
user's home dir will be created with 755 permissions which is a much
more sane default than before.

Back to the / fallback.

Right now, what happens is this:

If /home/$USER exists, but cd to it fails due to missing permissions,
the shell will end up in the former current directory.  This is typically
/bin or /usr/bin.

If /home/$USER does not exist, the /etc/profile mechanism kicks in.
If /home does not have sufficient permissions for the user to create
his/her own home dir, something like this will happen:

  mkdir: cannot create directory `/home/corinna': Permission denied
  /home/corinna could not be created.
  Setting HOME to /cygdrive/c/Users/corinna/AppData/Local/Temp.

When not using bash, but tcsh, the following happens:

  mkdir: cannot create directory `/home/corinna': Permission denied
  cd: Can't change to home directory.
  [/usr/bin]$

I don't see anything wrong with this behaviour.  Maybe /etc/profile
should choose / rather than $TEMP as fallback HOME dir?  And maybe tcsh
should align its behaviour and set HOME to / as well if mkdir fails to
work?

What other pathological case am I missing?


Corinna

-- 
Corinna Vinschen                  Please, send mails regarding Cygwin to
Cygwin Project Co-Leader          cygwin AT cygwin DOT com
Red Hat



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