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Perform logical replication actions as the table owner.

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Up until now, logical replication actions have been performed as the
subscription owner, who will generally be a superuser.  Commit
cec57b1a0fbcd3833086ba686897c5883e0a2afc documented hazards
associated with that situation, namely, that any user who owns a
table on the subscriber side could assume the privileges of the
subscription owner by attaching a trigger, expression index, or
some other kind of executable code to it. As a remedy, it suggested
not creating configurations where users who are not fully trusted
own tables on the subscriber.

Although that will work, it basically precludes using logical
replication in the way that people typically want to use it,
namely, to replicate a database from one node to another
without necessarily having any restrictions on which database
users can own tables. So, instead, change logical replication to
execute INSERT, UPDATE, DELETE, and TRUNCATE operations as the
table owner when they are replicated.

Since this involves switching the active user frequently within
a session that is authenticated as the subscription user, also
impose SECURITY_RESTRICTED_OPERATION restrictions on logical
replication code. As an exception, if the table owner can SET
ROLE to the subscription owner, these restrictions have no
security value, so don't impose them in that case.

Subscription owners are now required to have the ability to
SET ROLE to every role that owns a table that the subscription
is replicating. If they don't, replication will fail. Superusers,
who normally own subscriptions, satisfy this property by default.
Non-superusers users who own subscriptions will need to be
granted the roles that own relevant tables.

Patch by me, reviewed (but not necessarily in its entirety) by
Jelte Fennema, Jeff Davis, and Noah Misch.

Discussion: http://postgr.es/m/CA+TgmoaSCkg9ww9oppPqqs+9RVqCexYCE6Aq=UsYPfnOoDeFkw@mail.gmail.com
This commit is contained in:
Robert Haas 2023-04-04 11:25:23 -04:00
parent 3077324b03
commit 1e10d49b65
9 changed files with 250 additions and 109 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

25
doc/src/sgml/logical-replication.sgml
View File

@ -1729,19 +1729,6 @@ CONTEXT: processing remote data for replication origin "pg_16395" during "INSER
<sect1 id="logical-replication-security">
<title>Security</title>
<para>
A user able to modify the schema of subscriber-side tables can execute
arbitrary code as the role which owns any subscription which modifies those tables. Limit ownership
and <literal>TRIGGER</literal> privilege on such tables to trusted roles.
Moreover, if untrusted users can create tables, use only
publications that list tables explicitly. That is to say, create a
subscription
<link linkend="sql-createpublication-for-all-tables"><literal>FOR ALL TABLES</literal></link>
or <link linkend="sql-createpublication-for-tables-in-schema"><literal>FOR TABLES IN SCHEMA</literal></link>
only when superusers trust every user permitted to create a non-temp table
on the publisher or the subscriber.
</para>
<para>
The role used for the replication connection must have
the <literal>REPLICATION</literal> attribute (or be a superuser). If the
@ -1784,12 +1771,18 @@ CONTEXT: processing remote data for replication origin "pg_16395" during "INSER
</para>
<para>
To create a subscription, the user must be a superuser.
To create a subscription, the user must have the privileges of the
the <literal>pg_create_subscription</literal> role, as well as
<literal>CREATE</literal> privileges on the database.
</para>
<para>
The subscription apply process will run in the local database with the
privileges of the subscription owner.
The subscription apply process will, at a session level, run with the
privileges of the subscription owner. However, when performing an insert,
update, delete, or truncate operation on a particular table, it will switch
roles to the table owner and perform the operation with the table owner's
privileges. This means that the subscription owner needs to be able to
<literal>SET ROLE</literal> to each role that owns a replicated table.
</para>
<para>

20
src/backend/commands/tablecmds.c
View File

@ -103,6 +103,7 @@
#include "utils/syscache.h"
#include "utils/timestamp.h"
#include "utils/typcache.h"
#include "utils/usercontext.h"
/*
* ON COMMIT action list
@ -1762,7 +1763,7 @@ ExecuteTruncate(TruncateStmt *stmt)
}
ExecuteTruncateGuts(rels, relids, relids_logged,
stmt->behavior, stmt->restart_seqs);
stmt->behavior, stmt->restart_seqs, false);
/* And close the rels */
foreach(cell, rels)
@ -1790,7 +1791,8 @@ void
ExecuteTruncateGuts(List *explicit_rels,
List *relids,
List *relids_logged,
DropBehavior behavior, bool restart_seqs)
DropBehavior behavior, bool restart_seqs,
bool run_as_table_owner)
{
List *rels;
List *seq_relids = NIL;
@ -1929,7 +1931,14 @@ ExecuteTruncateGuts(List *explicit_rels,
resultRelInfo = resultRelInfos;
foreach(cell, rels)
{
UserContext ucxt;
if (run_as_table_owner)
SwitchToUntrustedUser(resultRelInfo->ri_RelationDesc->rd_rel->relowner,
&ucxt);
ExecBSTruncateTriggers(estate, resultRelInfo);
if (run_as_table_owner)
RestoreUserContext(&ucxt);
resultRelInfo++;
}
@ -2134,7 +2143,14 @@ ExecuteTruncateGuts(List *explicit_rels,
resultRelInfo = resultRelInfos;
foreach(cell, rels)
{
UserContext ucxt;
if (run_as_table_owner)
SwitchToUntrustedUser(resultRelInfo->ri_RelationDesc->rd_rel->relowner,
&ucxt);
ExecASTruncateTriggers(estate, resultRelInfo);
if (run_as_table_owner)
RestoreUserContext(&ucxt);
resultRelInfo++;
}

22
src/backend/replication/logical/worker.c
View File

@ -207,6 +207,7 @@
#include "utils/rls.h"
#include "utils/syscache.h"
#include "utils/timeout.h"
#include "utils/usercontext.h"
#define NAPTIME_PER_CYCLE 1000 /* max sleep time between cycles (1s) */
@ -2395,6 +2396,7 @@ apply_handle_insert(StringInfo s)
LogicalRepRelMapEntry *rel;
LogicalRepTupleData newtup;
LogicalRepRelId relid;
UserContext ucxt;
ApplyExecutionData *edata;
EState *estate;
TupleTableSlot *remoteslot;
@ -2423,6 +2425,9 @@ apply_handle_insert(StringInfo s)
return;
}
/* Make sure that any user-supplied code runs as the table owner. */
SwitchToUntrustedUser(rel->localrel->rd_rel->relowner, &ucxt);
/* Set relation for error callback */
apply_error_callback_arg.rel = rel;
@ -2452,6 +2457,8 @@ apply_handle_insert(StringInfo s)
/* Reset relation for error callback */
apply_error_callback_arg.rel = NULL;
RestoreUserContext(&ucxt);
logicalrep_rel_close(rel, NoLock);
end_replication_step();
@ -2530,6 +2537,7 @@ apply_handle_update(StringInfo s)
{
LogicalRepRelMapEntry *rel;
LogicalRepRelId relid;
UserContext ucxt;
ApplyExecutionData *edata;
EState *estate;
LogicalRepTupleData oldtup;
@ -2569,6 +2577,9 @@ apply_handle_update(StringInfo s)
/* Check if we can do the update. */
check_relation_updatable(rel);
/* Make sure that any user-supplied code runs as the table owner. */
SwitchToUntrustedUser(rel->localrel->rd_rel->relowner, &ucxt);
/* Initialize the executor state. */
edata = create_edata_for_relation(rel);
estate = edata->estate;
@ -2619,6 +2630,8 @@ apply_handle_update(StringInfo s)
/* Reset relation for error callback */
apply_error_callback_arg.rel = NULL;
RestoreUserContext(&ucxt);
logicalrep_rel_close(rel, NoLock);
end_replication_step();
@ -2702,6 +2715,7 @@ apply_handle_delete(StringInfo s)
LogicalRepRelMapEntry *rel;
LogicalRepTupleData oldtup;
LogicalRepRelId relid;
UserContext ucxt;
ApplyExecutionData *edata;
EState *estate;
TupleTableSlot *remoteslot;
@ -2736,6 +2750,9 @@ apply_handle_delete(StringInfo s)
/* Check if we can do the delete. */
check_relation_updatable(rel);
/* Make sure that any user-supplied code runs as the table owner. */
SwitchToUntrustedUser(rel->localrel->rd_rel->relowner, &ucxt);
/* Initialize the executor state. */
edata = create_edata_for_relation(rel);
estate = edata->estate;
@ -2761,6 +2778,8 @@ apply_handle_delete(StringInfo s)
/* Reset relation for error callback */
apply_error_callback_arg.rel = NULL;
RestoreUserContext(&ucxt);
logicalrep_rel_close(rel, NoLock);
end_replication_step();
@ -3211,7 +3230,8 @@ apply_handle_truncate(StringInfo s)
relids,
relids_logged,
DROP_RESTRICT,
restart_seqs);
restart_seqs,
true);
foreach(lc, remote_rels)
{
LogicalRepRelMapEntry *rel = lfirst(lc);

3
src/backend/utils/init/Makefile
View File

@ -15,6 +15,7 @@ include $(top_builddir)/src/Makefile.global
OBJS = \
globals.o \
miscinit.o \
postinit.o
postinit.o \
usercontext.o
include $(top_srcdir)/src/backend/common.mk

3
src/backend/utils/init/meson.build
View File

@ -3,4 +3,5 @@
backend_sources += files(
'globals.c',
'miscinit.c',
'postinit.c')
'postinit.c',
'usercontext.c')

92
src/backend/utils/init/usercontext.c Normal file
View File

@ -0,0 +1,92 @@
/*-------------------------------------------------------------------------
*
* usercontext.c
* Convenience functions for running code as a different database user.
*
* Portions Copyright (c) 1996-2023, PostgreSQL Global Development Group
* Portions Copyright (c) 1994, Regents of the University of California
*
*
* IDENTIFICATION
* src/backend/utils/init/usercontext.c
*
*-------------------------------------------------------------------------
*/
#include "postgres.h"
#include "miscadmin.h"
#include "utils/acl.h"
#include "utils/guc.h"
#include "utils/usercontext.h"
/*
* Temporarily switch to a new user ID.
*
* If the current user doesn't have permission to SET ROLE to the new user,
* an ERROR occurs.
*
* If the new user doesn't have permission to SET ROLE to the current user,
* SECURITY_RESTRICTED_OPERATION is imposed and a new GUC nest level is
* created so that any settings changes can be rolled back.
*/
void
SwitchToUntrustedUser(Oid userid, UserContext *context)
{
/* Get the current user ID and security context. */
GetUserIdAndSecContext(&context->save_userid,
&context->save_sec_context);
/* Check that we have sufficient privileges to assume the target role. */
if (!member_can_set_role(context->save_userid, userid))
ereport(ERROR,
(errcode(ERRCODE_INSUFFICIENT_PRIVILEGE),
errmsg("role \"%s\" cannot SET ROLE to \"%s\"",
GetUserNameFromId(context->save_userid, false),
GetUserNameFromId(userid, false))));
/*
* Try to prevent the user to which we're switching from assuming the
* privileges of the current user, unless they can SET ROLE to that user
* anyway.
*/
if (member_can_set_role(userid, context->save_userid))
{
/*
* Each user can SET ROLE to the other, so there's no point in
* imposing any security restrictions. Just let the user do whatever
* they want.
*/
SetUserIdAndSecContext(userid, context->save_sec_context);
context->save_nestlevel = -1;
}
else
{
int sec_context = context->save_sec_context;
/*
* This user can SET ROLE to the target user, but not the other way
* around, so protect ourselves against the target user by setting
* SECURITY_RESTRICTED_OPERATION to prevent certain changes to the
* session state. Also set up a new GUC nest level, so that we can roll
* back any GUC changes that may be made by code running as the target
* user, inasmuch as they could be malicious.
*/
sec_context |= SECURITY_RESTRICTED_OPERATION;
SetUserIdAndSecContext(userid, sec_context);
context->save_nestlevel = NewGUCNestLevel();
}
}
/*
* Switch back to the original user ID.
*
* If we created a new GUC nest level, also role back any changes that were
* made within it.
*/
void
RestoreUserContext(UserContext *context)
{
if (context->save_nestlevel != -1)
AtEOXact_GUC(false, context->save_nestlevel);
SetUserIdAndSecContext(context->save_userid, context->save_sec_context);
}

3
src/include/commands/tablecmds.h
View File

@ -60,7 +60,8 @@ extern void ExecuteTruncateGuts(List *explicit_rels,
List *relids,
List *relids_logged,
DropBehavior behavior,
bool restart_seqs);
bool restart_seqs,
bool run_as_table_owner);
extern void SetRelationHasSubclass(Oid relationId, bool relhassubclass);

26
src/include/utils/usercontext.h Normal file
View File

@ -0,0 +1,26 @@
/*-------------------------------------------------------------------------
*
* usercontext.h
* Convenience functions for running code as a different database user.
*
*-------------------------------------------------------------------------
*/
#ifndef USERCONTEXT_H
#define USERCONTEXT_H
/*
* When temporarily changing to run as a different user, this structure
* holds the details needed to restore the original state.
*/
typedef struct UserContext
{
Oid save_userid;
int save_sec_context;
int save_nestlevel;
} UserContext;
/* Function prototypes. */
extern void SwitchToUntrustedUser(Oid userid, UserContext *context);
extern void RestoreUserContext(UserContext *context);
#endif /* USERCONTEXT_H */

165
src/test/subscription/t/027_nosuperuser.pl
View File

@ -76,22 +76,6 @@ sub grant_superuser
ALTER ROLE $role SUPERUSER));
}
sub revoke_bypassrls
{
my ($role) = @_;
$node_subscriber->safe_psql(
'postgres', qq(
ALTER ROLE $role NOBYPASSRLS));
}
sub grant_bypassrls
{
my ($role) = @_;
$node_subscriber->safe_psql(
'postgres', qq(
ALTER ROLE $role BYPASSRLS));
}
# Create publisher and subscriber nodes with schemas owned and published by
# "regress_alice" but subscribed and replicated by different role
# "regress_admin". For partitioned tables, layout the partitions differently
@ -177,59 +161,32 @@ expect_failure(
2,
5,
7,
qr/ERROR: ( [A-Z0-9]+:)? permission denied for table unpartitioned/msi,
qr/ERROR: ( [A-Z0-9]+:)? role "regress_admin" cannot SET ROLE to "regress_alice"/msi,
"non-superuser admin fails to replicate update");
grant_superuser("regress_admin");
expect_replication("alice.unpartitioned", 2, 7, 9,
"admin with restored superuser privilege replicates update");
# Grant INSERT, UPDATE, DELETE privileges on the target tables to
# "regress_admin" so that superuser privileges are not necessary for
# replication.
#
# Note that UPDATE and DELETE also require SELECT privileges, which
# will be granted in subsequent test.
#
# Privileges on the target role suffice for non-superuser replication.
$node_subscriber->safe_psql(
'postgres', qq(
ALTER ROLE regress_admin NOSUPERUSER;
SET SESSION AUTHORIZATION regress_alice;
GRANT INSERT,UPDATE,DELETE ON
alice.unpartitioned,
alice.hashpart, alice.hashpart_a, alice.hashpart_b
TO regress_admin;
REVOKE SELECT ON alice.unpartitioned FROM regress_admin;
GRANT regress_alice TO regress_admin;
));
publish_insert("alice.unpartitioned", 11);
expect_replication("alice.unpartitioned", 3, 7, 11,
"nosuperuser admin with INSERT privileges can replicate into unpartitioned"
"nosuperuser admin with privileges on role can replicate INSERT into unpartitioned"
);
publish_update("alice.unpartitioned", 7 => 13);
expect_failure(
"alice.unpartitioned",
3,
7,
11,
qr/ERROR: ( [A-Z0-9]+:)? permission denied for table unpartitioned/msi,
"non-superuser admin without SELECT privileges fails to replicate update"
expect_replication("alice.unpartitioned", 3, 9, 13,
"nosuperuser admin with privileges on role can replicate UPDATE into unpartitioned"
);
# Now grant SELECT
#
$node_subscriber->safe_psql(
'postgres', qq(
SET SESSION AUTHORIZATION regress_alice;
GRANT SELECT ON
alice.unpartitioned,
alice.hashpart, alice.hashpart_a, alice.hashpart_b
TO regress_admin;
));
publish_delete("alice.unpartitioned", 9);
expect_replication("alice.unpartitioned", 2, 11, 13,
"nosuperuser admin with all table privileges can replicate into unpartitioned"
"nosuperuser admin with privileges on role can replicate DELETE into unpartitioned"
);
# Test partitioning
@ -240,80 +197,114 @@ publish_insert("alice.hashpart", 103);
publish_update("alice.hashpart", 102 => 120);
publish_delete("alice.hashpart", 101);
expect_replication("alice.hashpart", 2, 103, 120,
"nosuperuser admin with all table privileges can replicate into hashpart"
"nosuperuser admin with privileges on role can replicate into hashpart"
);
# Enable RLS on the target table and check that "regress_admin" can
# only replicate into it when superuser or bypassrls.
#
# Force RLS on the target table and check that replication fails.
$node_subscriber->safe_psql(
'postgres', qq(
SET SESSION AUTHORIZATION regress_alice;
ALTER TABLE alice.unpartitioned ENABLE ROW LEVEL SECURITY;
ALTER TABLE alice.unpartitioned FORCE ROW LEVEL SECURITY;
));
revoke_superuser("regress_admin");
publish_insert("alice.unpartitioned", 15);
expect_failure(
"alice.unpartitioned",
2,
11,
13,
qr/ERROR: ( [A-Z0-9]+:)? user "regress_admin" cannot replicate into relation with row-level security enabled: "unpartitioned\w*"/msi,
"non-superuser admin fails to replicate insert into rls enabled table");
grant_superuser("regress_admin");
qr/ERROR: ( [A-Z0-9]+:)? user "regress_alice" cannot replicate into relation with row-level security enabled: "unpartitioned\w*"/msi,
"replication of insert into table with forced rls fails");
# Since replication acts as the table owner, replication will succeed if we don't force it.
$node_subscriber->safe_psql(
'postgres', qq(
ALTER TABLE alice.unpartitioned NO FORCE ROW LEVEL SECURITY;
));
expect_replication("alice.unpartitioned", 3, 11, 15,
"admin with restored superuser privilege replicates insert into rls enabled unpartitioned"
"non-superuser admin can replicate insert if rls is not forced"
);
revoke_superuser("regress_admin");
$node_subscriber->safe_psql(
'postgres', qq(
ALTER TABLE alice.unpartitioned FORCE ROW LEVEL SECURITY;
));
publish_update("alice.unpartitioned", 11 => 17);
expect_failure(
"alice.unpartitioned",
3,
11,
15,
qr/ERROR: ( [A-Z0-9]+:)? user "regress_admin" cannot replicate into relation with row-level security enabled: "unpartitioned\w*"/msi,
"non-superuser admin fails to replicate update into rls enabled unpartitioned"
qr/ERROR: ( [A-Z0-9]+:)? user "regress_alice" cannot replicate into relation with row-level security enabled: "unpartitioned\w*"/msi,
"replication of update into table with forced rls fails"
);
grant_bypassrls("regress_admin");
$node_subscriber->safe_psql(
'postgres', qq(
ALTER TABLE alice.unpartitioned NO FORCE ROW LEVEL SECURITY;
));
expect_replication("alice.unpartitioned", 3, 13, 17,
"admin with bypassrls replicates update into rls enabled unpartitioned");
"non-superuser admin can replicate update if rls is not forced");
revoke_bypassrls("regress_admin");
publish_delete("alice.unpartitioned", 13);
# Remove some of alice's privileges on her own table. Then replication should fail.
$node_subscriber->safe_psql(
'postgres', qq(
REVOKE SELECT, INSERT ON alice.unpartitioned FROM regress_alice;
));
publish_insert("alice.unpartitioned", 19);
expect_failure(
"alice.unpartitioned",
3,
13,
17,
qr/ERROR: ( [A-Z0-9]+:)? user "regress_admin" cannot replicate into relation with row-level security enabled: "unpartitioned\w*"/msi,
"non-superuser admin without bypassrls fails to replicate delete into rls enabled unpartitioned"
qr/ERROR: ( [A-Z0-9]+:)? permission denied for table unpartitioned/msi,
"replication of insert fails if table owner lacks insert permission"
);
grant_bypassrls("regress_admin");
expect_replication("alice.unpartitioned", 2, 15, 17,
"admin with bypassrls replicates delete into rls enabled unpartitioned");
grant_superuser("regress_admin");
# Alter the subscription owner to "regress_alice". She has neither superuser
# nor bypassrls, but as the table owner should be able to replicate.
#
# alice needs INSERT but not SELECT to replicate an INSERT.
$node_subscriber->safe_psql(
'postgres', qq(
ALTER SUBSCRIPTION admin_sub DISABLE;
ALTER ROLE regress_alice SUPERUSER;
ALTER SUBSCRIPTION admin_sub OWNER TO regress_alice;
ALTER ROLE regress_alice NOSUPERUSER;
ALTER SUBSCRIPTION admin_sub ENABLE;
GRANT INSERT ON alice.unpartitioned TO regress_alice;
));
expect_replication("alice.unpartitioned", 4, 13, 19,
"restoring insert permission permits replication to continue");
publish_insert("alice.unpartitioned", 23);
publish_update("alice.unpartitioned", 15 => 25);
publish_delete("alice.unpartitioned", 17);
expect_replication("alice.unpartitioned", 2, 23, 25,
"nosuperuser nobypassrls table owner can replicate delete into unpartitioned despite rls"
# Now let's try an UPDATE and a DELETE.
$node_subscriber->safe_psql(
'postgres', qq(
REVOKE UPDATE, DELETE ON alice.unpartitioned FROM regress_alice;
));
publish_update("alice.unpartitioned", 13 => 21);
publish_delete("alice.unpartitioned", 15);
expect_failure(
"alice.unpartitioned",
4,
13,
19,
qr/ERROR: ( [A-Z0-9]+:)? permission denied for table unpartitioned/msi,
"replication of update/delete fails if table owner lacks corresponding permission"
);
# Restoring UPDATE and DELETE is insufficient.
$node_subscriber->safe_psql(
'postgres', qq(
GRANT UPDATE, DELETE ON alice.unpartitioned TO regress_alice;
));
expect_failure(
"alice.unpartitioned",
4,
13,
19,
qr/ERROR: ( [A-Z0-9]+:)? permission denied for table unpartitioned/msi,
"replication of update/delete fails if table owner lacks SELECT permission"
);
# alice needs INSERT but not SELECT to replicate an INSERT.
$node_subscriber->safe_psql(
'postgres', qq(
GRANT SELECT ON alice.unpartitioned TO regress_alice;
));
expect_replication("alice.unpartitioned", 3, 17, 21,
"restoring SELECT permission permits replication to continue");
done_testing();