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Re: Recursive operations and authz

From: C. Michael Pilato <cmpilato_at_collab.net>
Date: Wed, 13 May 2015 09:24:08 -0400

On 05/13/2015 02:21 AM, Stefan Fuhrmann wrote:
> Hi devs,
> At WANdisco, people have been playing with the new
> wildcard support for authz (see authz-performance branch)
> and ran into an interesting problem.

[Details snipped. Welcome to 2004, where CollabNet ran into the same
issues with the proprietary regexp-based authz implementation we shipped
in our enterprise products.]

> My suggestion is to relax the requirements as follows:
> COPY & MOVE still require recursive read access on
> the source but only non-recursive write access on the
> destination. Thus it becomes possible to protect data
> in branches and tags right from their inception without
> relaxing read access requirements to existing data. The
> attached patch achieves just that.
> I have 3 questions:
> (1) Is there something fundamentally wrong with this
> approach, e.g. braking major use-cases?
> (2) Should we require write access to target and target's
> parent folder (as done by the patch) or just to the target's
> parent folder?
> (3) Should we (optionally?) reduce the access rights reqs
> for DELETE similarly such that no recursive write access
> is needed? That seems risky but would be symmetrical
> to creating copies with r/o or n/a sub-paths. MOVE would
> be updated accordingly (always the same reqs as a COPY
> + DELETE).

Well, the use-case being broken here is kinda the obvious one: I
shouldn't have permission to create/delete some path /foo/bar (it's a
system-critical file that shouldn't go away, or a password-bearing file
path blocked by the VC system because devs keep stupidly committing
them, or...), but you've provided and end-around for me to do so. :-)
In the copy and move scenarios, you're allowing me to create a path I
can't later delete or further modify. Now, while this is a very handy
semantic for tag creation[1], it's also something an administrator
should be able to make a conscious decision about, not just an
unfortunate side-effect of an effort to make the code faster.

Subversion's path-based authz subsystem is about paths, not nodes as we
devs think of them. Our users have generally not been asked to consider
a copy, addition, or deletion of an item to be changes made to the
parent of that item. So the changes you're suggesting are not merely
ones of functionality, but ones of philosophy. I lean towards thinking
that falls outside the scope of acceptable changes in behavior in the
1.x line *unless* you can find a way to, via configuration, allow
administrators to explicitly toggle this new paradigm.

-- Mike

[1] Along with regexp access rules, CollabNet has for many years
supported this tag creation use-case by splitting the "write" permission
into multiple ones: "add", "copy", "delete", and "modify". Something
Subversion should consider?
Received on 2015-05-13 15:25:47 CEST

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