linux-kernel - Re: [RFC v7 26/41] richacl: Apply the file masks to a richacl

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Message-ID: <20150923203357.GC30521@fieldses.org>
Date:	Wed, 23 Sep 2015 16:33:57 -0400
From:	"J. Bruce Fields" <bfields@...ldses.org>
To:	Andreas Gruenbacher <agruenba@...hat.com>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	linux-fsdevel <linux-fsdevel@...r.kernel.org>,
	linux-nfs@...r.kernel.org, linux-api@...r.kernel.org,
	linux-cifs@...r.kernel.org, linux-security-module@...r.kernel.org,
	Andreas Gruenbacher <agruen@...nel.org>
Subject: Re: [RFC v7 26/41] richacl: Apply the file masks to a richacl

On Wed, Sep 23, 2015 at 10:29:40PM +0200, Andreas Gruenbacher wrote:
> 2015-09-23 21:18 GMT+02:00 J. Bruce Fields <bfields@...ldses.org>:
> > On Tue, Sep 22, 2015 at 03:11:08PM -0400, bfields wrote:
> >> user aces like owner aces what you intended to do,
> >> and if so, why?
> >
> > That does look wrong to me; in an example like:
> >
> >         file owner bfields
> >         mask 0700, not WRITE_THROUGH
> >         bfields:rwx::allow
> >
> > The permission algorithm grants nothing to anyone, but it looks to me
> > like richacl_apply_masks just leaves this as
> >
> >         bfields:rwx::allow
> >
> > but it would give the right result (an empty/deny-all ACL) if it weren't
> > for this odd case here.
> 
> In POSIX ACLs, only the entry that best matches the process determines
> the access permissions. For the file owner, this would always be the
> "user::" entry, and such an entry always exists.
> 
> In richacls, permissions from multiple entries do accumulate; the
> permission check algorithm does not pick a "best match". When bfields
> owns a file and a "bfields:rwx::allow" entry exists, denying rwx
> access to bfields would be very surprising.

The same could be said if there's a group-i-belong-to:rwx::allow entry,
do we make that exception too?

--b.

> It makes more sense to put
> user entries that match the current owner into the owner class, and
> apply the owner mask instead of the group mask. This was working in an
> earlier version but apparently broke at some point.
> 
> So the result that richacl_apply_masks computes here is correct, and
> the permission check algorithm needs a little fix.
> 
> Thanks,
> Andreas
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