#
# SPDX-License-Identifier: AGPL-3.0
+require '20200501150153_permission_table_constants'
+
class PermissionTable < ActiveRecord::Migration[5.0]
def up
# This is a major migration. We are replacing the
# permissions system. Updating trashed items follows a similar
# (but less complicated) strategy to updating permissions, so it
# may be helpful to look at that first.
- #
ActiveRecord::Base.connection.execute "DROP MATERIALIZED VIEW IF EXISTS materialized_permission_view;"
drop_table :permission_refresh_lock
)
select uuid, trash_at from project_subtree;
$$;
-}
-
- ActiveRecord::Base.connection.execute %{
-create or replace function compute_trashed ()
-returns table (uuid varchar(27), trash_at timestamp)
-STABLE
-language SQL
-as $$
-/* Helper function to populate trashed_groups table. This starts with
- each group owned by a user and computes the subtree under that
- group to find any groups that are trashed.
-*/
-select ps.target_uuid as group_uuid, ps.trash_at from groups,
- lateral project_subtree_with_trash_at(groups.uuid, groups.trash_at) ps
- where groups.owner_uuid like '_____-tpzed-_______________'
-$$;
}
# Now populate the table. For a non-test databse this is the only
# time this ever happens, after this the trash table is updated
# incrementally. See app/models/group.rb#update_trash
- ActiveRecord::Base.connection.execute("INSERT INTO trashed_groups select * from compute_trashed()")
+ refresh_trashed
# The table to store the flattened permissions. This is almost
# exactly the same as the old materalized_permission_view except
}
# Merge all permission relationships into a single view. This
- # consists of: groups (projects) owning things, users owning
- # things, and explicit permission links.
+ # consists of: groups owned by users and projects, users owned
+ # by other users, users have permission on themselves,
+ # and explicit permission links.
#
- # Fun fact, a SQL view gets inlined into the query where it is
- # used, this enables the query planner to inject constraints, so
- # when using the view we only look up edges we plan to traverse
- # and avoid a brute force computation of all edges.
+ # A SQL view gets inlined into the query where it is used as a
+ # subquery. This enables the query planner to inject constraints,
+ # so it only has to look up edges it plans to traverse and avoid a brute
+ # force query of all edges.
ActiveRecord::Base.connection.execute %{
create view permission_graph_edges as
- select groups.owner_uuid as tail_uuid, groups.uuid as head_uuid, (3) as val from groups
+ select groups.owner_uuid as tail_uuid, groups.uuid as head_uuid,
+ (3) as val, groups.uuid as edge_id from groups
+union all
+ select users.owner_uuid as tail_uuid, users.uuid as head_uuid,
+ (3) as val, users.uuid as edge_id from users
union all
- select users.owner_uuid as tail_uuid, users.uuid as head_uuid, (3) as val from users
+ select users.uuid as tail_uuid, users.uuid as head_uuid,
+ (3) as val, '' as edge_id from users
union all
select links.tail_uuid,
links.head_uuid,
WHEN links.name = 'can_login' THEN 1
WHEN links.name = 'can_write' THEN 2
WHEN links.name = 'can_manage' THEN 3
- END as val
+ ELSE 0
+ END as val,
+ links.uuid as edge_id
from links
where links.link_class='permission'
}
- ActiveRecord::Base.connection.execute %{
-create or replace function search_permission_graph (starting_uuid varchar(27),
- starting_perm integer,
- override_edge_tail varchar(27) default null,
- override_edge_head varchar(27) default null,
- override_edge_perm integer default null)
- returns table (target_uuid varchar(27), val integer, traverse_owned bool)
-STABLE
-language SQL
-as $$
-/*
- From starting_uuid, perform a recursive self-join on the edges
- to follow chains of permissions. This is a breadth-first search
- of the permission graph. Permission is propagated across edges,
- which may narrow the permission for subsequent links (eg I start
- at can_manage but when traversing a can_read link everything
- touched through that link will only be can_read).
-
- Yields the set of objects that are potentially affected, and
- their permission levels granted by having starting_perm on
- starting_uuid.
-
- If starting_uuid is a user, this computes the entire set of
- permissions for that user (because it returns everything that is
- reachable by that user).
-
- Used by the compute_permission_subgraph function.
-*/
-WITH RECURSIVE
- traverse_graph(target_uuid, val, traverse_owned) as (
- values (starting_uuid, starting_perm,
- should_traverse_owned(starting_uuid, starting_perm))
- union
- (select edges.head_uuid,
- least(edges.val,
- traverse_graph.val,
- case traverse_graph.traverse_owned
- when true then null
- else 0
- end,
- case (edges.tail_uuid = override_edge_tail AND
- edges.head_uuid = override_edge_head)
- when true then override_edge_perm
- else null
- end),
- should_traverse_owned(edges.head_uuid, edges.val)
- from permission_graph_edges as edges, traverse_graph
- where traverse_graph.target_uuid = edges.tail_uuid))
- select target_uuid, max(val), bool_or(traverse_owned) from traverse_graph
- group by (target_uuid);
-$$;
+ # This is used to ensure that the permission edge passed into
+ # compute_permission_subgraph takes replaces the existing edge in
+ # the "edges" view that is about to be removed.
+ edge_perm = %{
+case (edges.edge_id = perm_edge_id)
+ when true then starting_perm
+ else edges.val
+ end
}
+ # The primary function to compute permissions for a subgraph.
+ # Comments on how it works are inline.
+ #
+ # Due to performance issues due to the query optimizer not
+ # working across function and "with" expression boundaries, I
+ # had to fall back on using string templates for repeated code
+ # in order to inline it.
+
ActiveRecord::Base.connection.execute %{
create or replace function compute_permission_subgraph (perm_origin_uuid varchar(27),
starting_uuid varchar(27),
- starting_perm integer)
+ starting_perm integer,
+ perm_edge_id varchar(27))
returns table (user_uuid varchar(27), target_uuid varchar(27), val integer, traverse_owned bool)
STABLE
language SQL
as $$
-/* perm_origin_uuid: The object that 'gets' or 'has' the permission.
+
+/* The purpose of this function is to compute the permissions for a
+ subgraph of the database, starting from a given edge. The newly
+ computed permissions are used to add and remove rows from the main
+ permissions table.
+
+ perm_origin_uuid: The object that 'gets' the permission.
starting_uuid: The starting object the permission applies to.
can_write, can_manage respectively, or 0 to revoke
permissions.
- This function is broken up into a number of clauses, described
- below.
-
- Note on query optimization:
-
- Each clause in a "with" statement is called a "common table
- expression" or CTE.
-
- In Postgres, they are evaluated in sequence and results of each CTE
- is stored in a temporary table. This means Postgres does not
- propagate constraints from later subqueries to earlier subqueries
- when they are CTEs.
-
- This is a problem if, for example, a later subquery chooses 10
- items out of a set of 1000000 defined by an earlier subquery,
- because it will always compute all 1000000 rows even if the query
- on the 1000000 rows could have been constrained. This is why
- permission_graph_edges is a view -- views are inlined so and can be
- optimized using external constraints.
-
- The query optimizer does sort the temporary tables for later use in
- joins.
-
- Final note, this query would have been almost impossible to write
- (and certainly impossible to read) without splitting it up using
- SQL "with" but unfortunately it also stumbles into a frustrating
- Postgres optimizer bug, see
- lib/refresh_permission_view.rb#update_permissions
- for details and a partial workaround.
+ perm_edge_id: Identifies the permission edge that is being updated.
+ Changes of ownership, this is starting_uuid.
+ For links, this is the uuid of the link object.
+ This is used to override the edge value in the database
+ with starting_perm. This is necessary when revoking
+ permissions because the update happens before edge is
+ actually removed.
*/
with
- /* Gets the initial set of objects potentially affected by the
- permission change, using search_permission_graph.
+ /* Starting from starting_uuid, determine the set of objects that
+ could be affected by this permission change.
+
+ Note: We don't traverse users unless it is an "identity"
+ permission (permission origin is self).
*/
perm_from_start(perm_origin_uuid, target_uuid, val, traverse_owned) as (
- select perm_origin_uuid, target_uuid, val, traverse_owned
- from search_permission_graph(starting_uuid,
- starting_perm,
- perm_origin_uuid,
- starting_uuid,
- starting_perm)),
-
- /* Finds other inbound edges that grant permissions on the objects
- in perm_from_start, and computes permissions that originate from
- those. This is required to handle the case where there is more
- than one path through which a user gets permission to an object.
- For example, a user owns a project and also shares it can_read
- with a group the user belongs to, adding the can_read link must
- not overwrite the existing can_manage permission granted by
- ownership.
+ #{PERM_QUERY_TEMPLATE % {:base_case => %{
+ values (perm_origin_uuid, starting_uuid, starting_perm,
+ should_traverse_owned(starting_uuid, starting_perm),
+ (perm_origin_uuid = starting_uuid or starting_uuid not like '_____-tpzed-_______________'))
+},
+:edge_perm => edge_perm
+} }),
+
+ /* Find other inbound edges that grant permissions to 'targets' in
+ perm_from_start, and compute permissions that originate from
+ those.
+
+ This is necessary for two reasons:
+
+ 1) Other users may have access to a subset of the objects
+ through other permission links than the one we started from.
+ If we don't recompute them, their permission will get dropped.
+
+ 2) There may be more than one path through which a user gets
+ permission to an object. For example, a user owns a project
+ and also shares it can_read with a group the user belongs
+ to. adding the can_read link must not overwrite the existing
+ can_manage permission granted by ownership.
*/
additional_perms(perm_origin_uuid, target_uuid, val, traverse_owned) as (
- select edges.tail_uuid as perm_origin_uuid, ps.target_uuid, ps.val,
- should_traverse_owned(ps.target_uuid, ps.val)
- from permission_graph_edges as edges,
- lateral search_permission_graph(edges.head_uuid,
- edges.val,
- perm_origin_uuid,
- starting_uuid,
- starting_perm) as ps
- where (not (edges.tail_uuid = perm_origin_uuid and
- edges.head_uuid = starting_uuid)) and
- edges.tail_uuid not in (select target_uuid from perm_from_start) and
- edges.head_uuid in (select target_uuid from perm_from_start)),
-
- /* Combines the permissions computed in the first two phases. */
- partial_perms(perm_origin_uuid, target_uuid, val, traverse_owned) as (
+ #{PERM_QUERY_TEMPLATE % {:base_case => %{
+ select edges.tail_uuid as origin_uuid, edges.head_uuid as target_uuid, edges.val,
+ should_traverse_owned(edges.head_uuid, edges.val),
+ edges.head_uuid like '_____-j7d0g-_______________'
+ from permission_graph_edges as edges
+ where edges.edge_id != perm_edge_id and
+ edges.tail_uuid not in (select target_uuid from perm_from_start where target_uuid like '_____-j7d0g-_______________') and
+ edges.head_uuid in (select target_uuid from perm_from_start)
+},
+:edge_perm => edge_perm
+} }),
+
+ /* Combine the permissions computed in the first two phases. */
+ all_perms(perm_origin_uuid, target_uuid, val, traverse_owned) as (
select * from perm_from_start
union all
select * from additional_perms
- ),
-
- /* If there are any users in the set of potentially affected objects
- and the user's owner was not traversed, recompute permissions for
- that user. This is required because users always have permission
- to themselves (identity property) which would be missing from the
- permission set if the user was traversed while computing
- permissions for another object.
- */
- user_identity_perms(perm_origin_uuid, target_uuid, val, traverse_owned) as (
- select users.uuid as perm_origin_uuid, ps.target_uuid, ps.val, ps.traverse_owned
- from users, lateral search_permission_graph(users.uuid,
- 3,
- perm_origin_uuid,
- starting_uuid,
- starting_perm) as ps
- where (users.owner_uuid not in (select target_uuid from partial_perms) or
- users.owner_uuid = users.uuid) and
- users.uuid in (select target_uuid from partial_perms)
- ),
-
- /* Combines all the computed permissions into one table. */
- all_perms(perm_origin_uuid, target_uuid, val, traverse_owned) as (
- select * from partial_perms
- union
- select * from user_identity_perms
)
/* The actual query that produces rows to be added or removed
Key insights:
- * Permissions are transitive (with some special cases involving
- users, this is controlled by the traverse_owned flag).
+ * For every group, the materialized_permissions lists all users
+ that can access to that group.
+
+ * The all_perms subquery has computed permissions on on a set of
+ objects for all inbound "origins", which are users or groups.
- * A user object can only gain permissions via an inbound edge,
- or appearing in the graph.
+ * Permissions through groups are transitive.
- * The materialized_permissions table includes the permission
- each user has on the tail end of each inbound edge.
+ We can infer:
- * The all_perms subquery has permissions for each object in the
- subgraph reachable from certain origin (tail end of an edge).
+ 1) The materialized_permissions table declares that user X has permission N on group Y
+ 2) The all_perms result has determined group Y has permission M on object Z
+ 3) Therefore, user X has permission min(N, M) on object Z
- * Therefore, for each user, we can compute user permissions on
- each object in subgraph by determining the permission the user
- has on each origin (tail end of an edge), joining that with the
- perm_origin_uuid column of all_perms, and taking the least() of
- the origin edge or all_perms val (because of the "least
- permission on the path" rule). If an object was reachable by
- more than one path (appears with more than one origin), we take
- the max() of the computed permissions.
+ This allows us to efficiently determine the set of users that
+ have permissions on the subset of objects, without having to
+ follow the chain of permission back up to find those users.
- * Finally, because users always have permission on themselves, the
- query also makes sure those permission rows are always
- returned.
+ In addition, because users always have permission on themselves, this
+ query also makes sure those permission rows are always
+ returned.
*/
select v.user_uuid, v.target_uuid, max(v.perm_level), bool_or(v.traverse_owned) from
(select m.user_uuid,
u.traverse_owned
from all_perms as u, materialized_permissions as m
where u.perm_origin_uuid = m.target_uuid AND m.traverse_owned
+ AND (m.user_uuid = m.target_uuid or m.target_uuid not like '_____-tpzed-_______________')
union all
- select perm_origin_uuid as user_uuid, target_uuid, val as perm_level, traverse_owned
+ select target_uuid as user_uuid, target_uuid, 3, true
from all_perms
- where all_perms.perm_origin_uuid like '_____-tpzed-_______________') as v
+ where all_perms.target_uuid like '_____-tpzed-_______________') as v
group by v.user_uuid, v.target_uuid
$$;
}
#
- # Populate the materialized_permissions by traversing permissions
+ # Populate materialized_permissions by traversing permissions
# starting at each user.
#
- ActiveRecord::Base.connection.execute %{
-INSERT INTO materialized_permissions
-select users.uuid, g.target_uuid, g.val, g.traverse_owned
-from users, lateral search_permission_graph(users.uuid, 3) as g where g.val > 0
-}
+ refresh_permissions
end
def down
drop_table :trashed_groups
ActiveRecord::Base.connection.execute "DROP function project_subtree_with_trash_at (varchar, timestamp);"
- ActiveRecord::Base.connection.execute "DROP function compute_trashed ();"
- ActiveRecord::Base.connection.execute "DROP function search_permission_graph(varchar, integer, varchar, varchar, integer);"
- ActiveRecord::Base.connection.execute "DROP function compute_permission_subgraph (varchar, varchar, integer);"
+ ActiveRecord::Base.connection.execute "DROP function compute_permission_subgraph (varchar, varchar, integer, varchar);"
ActiveRecord::Base.connection.execute "DROP function should_traverse_owned(varchar, integer);"
ActiveRecord::Base.connection.execute "DROP view permission_graph_edges;"
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