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Date: Wed, 1 Apr 2015 09:35:28 +0200
From: Corinna Vinschen <corinna-cygwin AT cygwin DOT com>
To: cygwin AT cygwin DOT com
Subject: Re: More about permissions
Message-ID: <20150401073528.GA493@calimero.vinschen.de>
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On Mar 31 20:41, Eliot Moss wrote:
> On 3/31/2015 4:55 PM, Andrey Repin wrote:
>=20
> >> I am not sure this particular program (CrashPlan) works that way.
> >
> >That's not program property, but the user you run the program from.
>=20
> Perhaps, but it runs as a background service.  I never explicitly said wh=
at
> user it runs as, etc.
>=20
> Looking in Services, I see is logs on as "Local System account".  Using
> Process Explorer, it appears to run without SEBackup/Restore privileges.
> Since the program has to request them itself as it runs, I don't see any
> good way to fix this.
>=20
> >I think i've explained it earlir, but here's it again:
> >In POSIX model, root have implicit permissions.
> >In Windows model, there NO implicit permissions at all. Everything shoul=
d be
> >explicitly assigned. I.e. SeBackupRestore privilege.
> >If you deny SYSTEM access to a file, OS will not be able to do anything =
about
> >it. Been there, blocked changes to cmd.exe when I was experimenting with=
 4NT.
> >(And cmd.exe was in fact renamed 4nt.exe.) None of the Windows autotools=
 were
> >able to get around it.
>=20
> Yes, I get that.  Hence my desire to grant SYSTEM:rwx on everything.
>=20
> What we seem to have ended up with here, though, is that the
> root privileges are explicit and are exposed in the ordinary permissions =
visible
> with, say, ls -l.

Huh?  ls -l (that is, stat(2)) shows the permissions in the same way as
they are computed on a POSIX system.  The mask value is just faked from
the existing permsissions, but other than that, it does what POSIX
1003.1e requires.

> This is not natural from a POSIX point of view (I claim);
> otherwise, we'd more or less show access of rwxrwxrwx on everything in PO=
SIX.

I don't grok that.  POSIX shows the permissions exactly as they are,
with the group permissions being the primary group perms or the mask
value if there is a mask.  On Cygwin the mask is faked, but it shows the
combined permissions of all non-primary users and groups, so it's a good
fake.  So in both cases the group permissions show you where's a
security problem.

Granting SYSTEM access to the kitchen sink is a Windows thingy, and a
bad one as well.  Rather than just asking the developers to enable the
SE_BACKUP_NAME/SE_RESTORE_NAME rights when needed, they now add full
access for SYSTEM and Administrators by default every time.  That's a
bad hack and totally unnecessary, too.

But Cygwin adds SE_BACKUP_NAME/SE_RESTORE_NAME rights to the processes
by default, so in theory you don't need full SYSTEM access inside your
Cygwin tree.


Corinna

--=20
Corinna Vinschen                  Please, send mails regarding Cygwin to
Cygwin Maintainer                 cygwin AT cygwin DOT com
Red Hat

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