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From "Jason Smith (Commented) (JIRA)" <>
Subject [jira] [Commented] (COUCHDB-1287) Inbox Database ("write-only" mode)
Date Mon, 21 Nov 2011 01:37:52 GMT


Jason Smith commented on COUCHDB-1287:

Hi, Benoit. No offense intended: as I re-read your patch I think you and I are making different
features under the same name. The following Bash script clarifies my critique. I think you
will agree that either (a) we are working on different things, with a name collision, "dropbox";
or (b) your patch is careless and dangerous.


# Given: admin user "admin" and normal users "amy" and "bob"
# New database
curl -X DELETE http://admin:admin@localhost:5984/db
curl -X PUT http://admin:admin@localhost:5984/db

# Create a document
curl -X PUT http://admin:admin@localhost:5984/db/doc1 -d '{"hello":"world"}'
curl -X PUT http://admin:admin@localhost:5984/db/doc2 -d '{"hello":"world"}'

# Amy is a member. Bob is not.
curl -X PUT http://admin:admin@localhost:5984/db/_security -d '{"members":{"names":["amy"]}}'

# Amy can open /db
curl --fail http://amy:amy@localhost:5984/db

# Bob cannot open /db
curl --fail http://bob:bob@localhost:5984/db

# Make a dropbox db
curl -X PUT http://admin:admin@localhost:5984/db/_security -d '{"members":{"names":["amy"]},

# Member amy cannot get a doc (regression)
curl --fail http://amy:amy@localhost:5984/db/doc1

# Non-member bob can get DB metadata (minor breach)
curl --fail http://bob:bob@localhost:5984/db

# Member amy cannot get _all_docs (regression)
curl --fail http://amy:amy@localhost:5984/db/_all_docs

# Non-member bob can fetch the entire database (major breach)
curl --fail http://bob:bob@localhost:5984/db/_changes?include_docs=true

# Anonymous users can fetch the entire database (major breach)
curl --fail http://localhost:5984/db/_changes?include_docs=true
> Inbox Database ("write-only" mode)
> ----------------------------------
>                 Key: COUCHDB-1287
>                 URL:
>             Project: CouchDB
>          Issue Type: New Feature
>          Components: HTTP Interface
>    Affects Versions: 1.2
>            Reporter: Jason Smith
>            Priority: Minor
>         Attachments: 0001-handle-dropbox-db.-Add-dropbox-true-to-security-obje.patch,
A_0001-Refactor-reader_acl-test-functions-into-a-loop.patch, A_0002-Refactor-the-actual-read-check-out-of-the-member-che.patch,
A_0003-Allow-non-member-writes-if-_security.members.allow_a.patch, B_0001-Refactor-reader_acl-test-functions-into-a-loop.patch,
B_0002-Refactor-the-actual-read-check-out-of-the-member-che.patch, B_0003-Allow-non-member-updates-if-_security.members.allow_.patch
> Currently, we can only grant combined read+write access in the _security object "members"
section. A user can either do both or neither. This prevents a very common requirement for
couch apps: sending private information from less-privileged users to more-privileged users.
> There is no (reasonable) way to make an "inbox" where anybody may create a doc for me,
but only I may read it. An inbox database allows user-to-user, or user-to-admin private messages.
(Not only chat messages, but asynchronous notifications--with a per-user inbox, perhaps even
service requests and responses.)
> There is no reason _security.members (formerly .readers) should control write access.
validate_doc_update() functions do this better.
> I propose a boolean flag, _security.members.allow_anonymous_writes. If it is true, then
CouchDB will allow document updates from non-members, giving validate_doc_update() the final
word on accepting or rejecting the update.
> Requirements:
> 1. Everything about _security stays the same (backward-compatible)
> 2. If members.allow_anonymous_writes === true, then most PUT and POSTs may proceed
> 3. All updates are still subject to approval by all validate_doc_update functions, same
as before.
> These are the known changes to the security model. I consider these all to be either
very unlikely in practice, or worth the trade-off.
> * If you write to an inbox DB, you know, for a time, a subset of its documents (but that's
the point)
> * An _update function could reveal a document to the user, with or without changing it.
However, an admin must install such a misguided update function.
> * You can launch timing attacks to learn information about validate_doc_update
>   * You might discover whether doc IDs exist in the DB or not
>   * You might discover a well-known open source validation function. You can look for
bugs in its source code.
> * Zero or more things which Jason can't think of

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