changefeedccl: add new fine-grained permissions

This change updates permissions semantics related to creating and managing changefeeds.

The `CONTROLCHANGEFEED` role option will be deprecated in the future (see cockroachdb#94757). With this change, usages of `CONTROLCHANGEFEED` will come with a deprecation warning. Its existing behavior (see rules for creating changefeeds below) remains the same.

The `SELECT` and `CHANGEFEED` privileges will be used for changefeeds henceforth:

The `SELECT` privilege on a set of tables allows a user to run core changefeeds against them.

The `CHANGEFEED` privilege on a set of tables allows a user to run enterprise changefeeds on them, and also manage the underlying changefeed job (ie. view, pause, cancel, and resume the job). Notably, a new cluster setting `changefeed.permissions.enforce_external_connections` is added and set to `false` by default. Enabling this setting restricts users with `CHANGEFEED` on a set of tables to create enterprise changefeeds into external connections only. To use a given external connection, a user typically needs the `USAGE` privilege on it.

Note `ALTER DEFAULT PRIVILEGES` can be used with both the `CHANGEFEED` and `SELECT` privileges to assign course-grained permissions (ie. assign permissions to all tables in a schema rather than manually assign them for each table).

Before this change, to create a changefeed, these checks were made in order:
(a) If the user has the `CONTROLCHANGEFEED` role, then they require the `SELECT`privilege
     on all targeted tables
(b) Otherwise, the user requires  the `CHANGEFEED` privilege on all targeted tables
With this change, these checks are updated:
(a) If the user has the `CONTROLCHANGEFEED` role, then they require the `SELECT`
     privilege on all targeted tables. Note: creating a changefeed this way will now produce a
     deprecation notice.
(b) If the changefeed is a core changefeed, they require the `SELECT` privilege on all targeted
     tables
(c) Otherwise, the user requires the `CHANGEFEED` privilege on all targeted tables. Note: If
     `changefeed.permissions.enforce_external_connections` (disabled by default) is set to true,
     then the user will only be able to create a changefeed into an external connection which they
     have the `USAGE` privilege on.

Before this change, to manage a changefeed job `J` (defined a viewing, pausing, resuming, and canceling), a user `U` could do so if they met at least one of the following conditions:
(a) `U` is an admin
(b) `U` is not an admin and `J` is owned by `U`  (only for SHOW JOBS)
(c) `U` is not an admin, `J` is not owned by an admin, and `U` has the `CONTROLJOB` role
With this change, the conditions are updated:
(a) `U` is an admin
(b) `U` is not an admin and `J` is owned by `U`  (only for `SHOW JOBS` or `SHOW
     CHANGEFEED JOBS`)
(c) `U` is not an admin, `J` is not owned by an admin, and `U` has the `CONTROLJOB` role
(d) `U` is not an admin, `J` is not owned by an admin, `J` is a changefeed job, and `U` has
     the `CHANGEFEED` privilege on targeted tables

Before this change, permissions related to altering changefeeds with `ALTER CHANGEFEED` were not explicitly defined (we did not have tests to assert its behavior, but there were some permissions checks regardless). Basically, a user needed access to view a job (ie. look up it’s job ID via `SHOW JOBS`) and they needed to be able to create a new job. After all, `ALTER CHANGEFEED` is essentially the same as creating a new job after stopping the old one.

With this change, the same rules apply: the user needs to be able to access the existing job and to be able to create a new changefeed with the new rules introduced in this change respectively.

Fixes: cockroachdb#94756
Fixes: cockroachdb#92261
Fixes: cockroachdb#87884
Fixes: cockroachdb#85082
Informs: cockroachdb#94759
Informs: cockroachdb#94757
Epic: CRDB-21508
Epic: CRDB-19709

Release note (enterprise change):

The `CONTROLCHANGEFEED` role option will be deprecated in the future (see cockroachdb#94757). With this change, usages of `CONTROLCHANGEFEED` will come with a deprecation warning. Its existing behavior (see rules for creating changefeeds above) remains the same.

The `SELECT` and `CHANGEFEED` privileges will be used for changefeeds henceforth:

The `SELECT` privilege on a set of tables allows a user to run core changefeeds against them.

The `CHANGEFEED` privilege on a set of tables allows a user to run enterprise changefeeds on them, and also manage the underlying changefeed job (ie. view, pause, cancel, and resume the job). Notably, a new cluster setting `changefeed.permissions.enforce_external_connections` is added and set to `false` by default. Enabling this setting restricts users with `CHANGEFEED` on a set of tables to create enterprise changefeeds into external connections only. To use a given external connection, a user typically needs the `USAGE` privilege on it.

Note `ALTER DEFAULT PRIVILEGES` can be used with both both the `CHANGEFEED` and `SELECT` privileges to assign coarse-grained permissions (ie. assign permissions to all tables in a schema rather than manually assign them for each table).

pkg/ccl/changefeedccl/BUILD.bazel

@@ -105,6 +105,7 @@ go_library(
         "//pkg/sql/sem/volatility",
         "//pkg/sql/sessiondatapb",
         "//pkg/sql/sqlutil",
+        "//pkg/sql/syntheticprivilege",
         "//pkg/sql/types",
         "//pkg/util",
         "//pkg/util/admission",
@@ -234,6 +235,7 @@ go_test(
         "//pkg/sql",
         "//pkg/sql/catalog",
         "//pkg/sql/catalog/bootstrap",
+        "//pkg/sql/catalog/catpb",
         "//pkg/sql/catalog/colinfo",
         "//pkg/sql/catalog/descbuilder",
         "//pkg/sql/catalog/descpb",

pkg/ccl/changefeedccl/alter_changefeed_stmt.go

@@ -100,6 +100,17 @@ func alterChangefeedPlanHook(
 			return err
 		}
 
+		jobPayload := job.Payload()
+
+		// Having control job is not enough to allow them to modify the changefeed.
+		canAccess, userErr, err := sql.JobTypeSpecificPrivilegeCheck(ctx, p, jobID, &jobPayload, false)
+		if err != nil {
+			return err
+		}
+		if !canAccess {
+			return userErr
+		}
+
 		prevDetails, ok := job.Details().(jobspb.ChangefeedDetails)
 		if !ok {
 			return errors.Errorf(`job %d is not changefeed job`, jobID)
@@ -123,11 +134,12 @@ func alterChangefeedPlanHook(
 			return err
 		}
 
-		newTargets, newProgress, newStatementTime, originalSpecs, err := generateNewTargets(
+		newTargets, newProgress, newStatementTime, originalSpecs, err := generateAndValidateNewTargets(
 			ctx, exprEval, p,
 			alterChangefeedStmt.Cmds,
 			newOptions.AsMap(), // TODO: Remove .AsMap()
 			prevDetails, job.Progress(),
+			newSinkURI,
 		)
 		if err != nil {
 			return err
@@ -320,14 +332,15 @@ func generateNewOpts(
 	return changefeedbase.MakeStatementOptions(newOptions), sinkURI, nil
 }
 
-func generateNewTargets(
+func generateAndValidateNewTargets(
 	ctx context.Context,
 	exprEval exprutil.Evaluator,
 	p sql.PlanHookState,
 	alterCmds tree.AlterChangefeedCmds,
 	opts map[string]string,
 	prevDetails jobspb.ChangefeedDetails,
 	prevProgress jobspb.Progress,
+	sinkURI string,
 ) (
 	tree.ChangefeedTargets,
 	*jobspb.Progress,
@@ -490,6 +503,7 @@ func generateNewTargets(
 			existingTargetSpans := fetchSpansForDescs(p, existingTargetDescs)
 			var newTargetDescs []catalog.Descriptor
 			for _, target := range v.Targets {
+
 				desc, found, err := getTargetDesc(ctx, p, descResolver, target.TableName)
 				if err != nil {
 					return nil, nil, hlc.Timestamp{}, nil, err
@@ -501,6 +515,7 @@ func generateNewTargets(
 						tree.ErrString(&target),
 					)
 				}
+
 				k := targetKey{TableID: desc.GetID(), FamilyName: target.FamilyName}
 				newTargets[k] = target
 				newTableDescs[desc.GetID()] = desc
@@ -546,6 +561,7 @@ func generateNewTargets(
 						tree.ErrString(&target),
 					)
 				}
+				newTableDescs[desc.GetID()] = desc
 				delete(newTargets, k)
 			}
 			telemetry.CountBucketed(telemetryPath+`.dropped_targets`, int64(len(v.Targets)))
@@ -580,6 +596,20 @@ func generateNewTargets(
 		newTargetList = append(newTargetList, target)
 	}
 
+	hasSelectPrivOnAllTables := true
+	hasChangefeedPrivOnAllTables := true
+	for _, desc := range newTableDescs {
+		hasSelect, hasChangefeed, err := checkPrivilegesForDescriptor(ctx, p, desc)
+		if err != nil {
+			return nil, nil, hlc.Timestamp{}, nil, err
+		}
+		hasSelectPrivOnAllTables = hasSelectPrivOnAllTables && hasSelect
+		hasChangefeedPrivOnAllTables = hasChangefeedPrivOnAllTables && hasChangefeed
+	}
+	if err := verifyUserCanCreateChangefeed(ctx, p, sinkURI, hasSelectPrivOnAllTables, hasChangefeedPrivOnAllTables); err != nil {
+		return nil, nil, hlc.Timestamp{}, nil, err
+	}
+
 	if err := validateNewTargets(ctx, p, newTargetList, newJobProgress, newJobStatementTime); err != nil {
 		return nil, nil, hlc.Timestamp{}, nil, err
 	}

pkg/ccl/changefeedccl/alter_changefeed_test.go

@@ -10,19 +10,25 @@ package changefeedccl
 
 import (
 	"context"
+	gosql "database/sql"
 	"fmt"
+	"net/url"
 	"sync/atomic"
 	"testing"
 	"time"
 
+	"github.com/cockroachdb/cockroach/pkg/base"
 	"github.com/cockroachdb/cockroach/pkg/ccl/changefeedccl/cdctest"
 	"github.com/cockroachdb/cockroach/pkg/ccl/changefeedccl/changefeedbase"
+	"github.com/cockroachdb/cockroach/pkg/ccl/utilccl"
 	"github.com/cockroachdb/cockroach/pkg/jobs"
 	"github.com/cockroachdb/cockroach/pkg/jobs/jobspb"
 	"github.com/cockroachdb/cockroach/pkg/keys"
 	"github.com/cockroachdb/cockroach/pkg/kv"
 	"github.com/cockroachdb/cockroach/pkg/roachpb"
+	"github.com/cockroachdb/cockroach/pkg/server"
 	"github.com/cockroachdb/cockroach/pkg/server/telemetry"
+	"github.com/cockroachdb/cockroach/pkg/sql/catalog/catpb"
 	"github.com/cockroachdb/cockroach/pkg/sql/catalog/desctestutils"
 	"github.com/cockroachdb/cockroach/pkg/sql/execinfra"
 	"github.com/cockroachdb/cockroach/pkg/sql/tests"
@@ -40,6 +46,155 @@ import (
 	"github.com/stretchr/testify/require"
 )
 
+// TestAlterChangefeedAddTargetPrivileges tests permissions for
+// users creating new changefeeds while altering them.
+func TestAlterChangefeedAddTargetPrivileges(t *testing.T) {
+	defer leaktest.AfterTest(t)()
+	defer log.Scope(t).Close(t)
+
+	srv, db, _ := serverutils.StartServer(t, base.TestServerArgs{
+		DisableDefaultTestTenant: true,
+		Knobs: base.TestingKnobs{
+			JobsTestingKnobs: jobs.NewTestingKnobsWithShortIntervals(),
+			DistSQL: &execinfra.TestingKnobs{
+				Changefeed: &TestingKnobs{
+					WrapSink: func(s Sink, _ jobspb.JobID) Sink {
+						if _, ok := s.(*externalConnectionKafkaSink); ok {
+							return s
+						}
+						return &externalConnectionKafkaSink{sink: s}
+					},
+				},
+			},
+		},
+	})
+	ctx := context.Background()
+	s := srv.(*server.TestServer)
+	defer s.Stopper().Stop(ctx)
+
+	rootDB := sqlutils.MakeSQLRunner(db)
+	rootDB.Exec(t, `CREATE TYPE type_a as enum ('a')`)
+	rootDB.Exec(t, `CREATE TABLE table_a (id int, type type_a)`)
+	rootDB.Exec(t, `CREATE TABLE table_b (id int, type type_a)`)
+	rootDB.Exec(t, `CREATE TABLE table_c (id int, type type_a)`)
+	rootDB.Exec(t, `CREATE USER feedCreator`)
+	rootDB.Exec(t, `GRANT SELECT ON table_a TO feedCreator`)
+	rootDB.Exec(t, `GRANT CHANGEFEED ON table_a TO feedCreator`)
+	rootDB.Exec(t, `CREATE EXTERNAL CONNECTION "first" AS 'kafka://nope'`)
+	rootDB.Exec(t, `GRANT USAGE ON EXTERNAL CONNECTION first TO feedCreator`)
+	rootDB.Exec(t, `INSERT INTO table_a(id) values (0)`)
+
+	rootDB.Exec(t, `SET CLUSTER SETTING kv.rangefeed.enabled = true`)
+	enableEnterprise := utilccl.TestingDisableEnterprise()
+	enableEnterprise()
+
+	withUser := func(t *testing.T, user string, fn func(*sqlutils.SQLRunner)) {
+		password := `password`
+		rootDB.Exec(t, fmt.Sprintf(`ALTER USER %s WITH PASSWORD '%s'`, user, password))
+
+		pgURL := url.URL{
+			Scheme: "postgres",
+			User:   url.UserPassword(user, password),
+			Host:   s.SQLAddr(),
+		}
+		db2, err := gosql.Open("postgres", pgURL.String())
+		if err != nil {
+			t.Fatal(err)
+		}
+		defer db2.Close()
+		userDB := sqlutils.MakeSQLRunner(db2)
+
+		fn(userDB)
+	}
+
+	t.Run("using-changefeed-grant", func(t *testing.T) {
+		rootDB.Exec(t, `CREATE EXTERNAL CONNECTION "second" AS 'kafka://nope'`)
+		rootDB.Exec(t, `CREATE USER user1`)
+		rootDB.Exec(t, `GRANT CHANGEFEED ON table_a TO user1`)
+
+		var jobID int
+		withUser(t, "feedCreator", func(userDB *sqlutils.SQLRunner) {
+			row := userDB.QueryRow(t, "CREATE CHANGEFEED for table_a INTO 'external://first'")
+			row.Scan(&jobID)
+			userDB.Exec(t, `PAUSE JOB $1`, jobID)
+			waitForJobStatus(userDB, t, catpb.JobID(jobID), `paused`)
+		})
+
+		// user1 is missing the CHANGEFEED privilege on table_b and table_c.
+		withUser(t, "user1", func(userDB *sqlutils.SQLRunner) {
+			userDB.ExpectErr(t,
+				"user user1 requires the CHANGEFEED privilege on all target tables to be able to run an enterprise changefeed",
+				fmt.Sprintf("ALTER CHANGEFEED %d ADD table_b, table_c set sink='external://second'", jobID),
+			)
+		})
+		rootDB.Exec(t, `GRANT CHANGEFEED ON table_b TO user1`)
+		withUser(t, "user1", func(userDB *sqlutils.SQLRunner) {
+			userDB.ExpectErr(t,
+				"user user1 requires the CHANGEFEED privilege on all target tables to be able to run an enterprise changefeed",
+				fmt.Sprintf("ALTER CHANGEFEED %d ADD table_b, table_c set sink='external://second'", jobID),
+			)
+		})
+		rootDB.Exec(t, `GRANT CHANGEFEED ON table_c TO user1`)
+		withUser(t, "user1", func(userDB *sqlutils.SQLRunner) {
+			userDB.Exec(t,
+				fmt.Sprintf("ALTER CHANGEFEED %d ADD table_b, table_c set sink='external://second'", jobID),
+			)
+		})
+
+		// With require_external_connection_sink enabled, the user requires USAGE on the external connection.
+		rootDB.Exec(t, "SET CLUSTER SETTING changefeed.permissions.require_external_connection_sink = true")
+		withUser(t, "user1", func(userDB *sqlutils.SQLRunner) {
+			userDB.ExpectErr(t,
+				"user user1 does not have USAGE privilege on external_connection second",
+				fmt.Sprintf("ALTER CHANGEFEED %d ADD table_b, table_c set sink='external://second'", jobID),
+			)
+		})
+		rootDB.Exec(t, `GRANT USAGE ON EXTERNAL CONNECTION second TO user1`)
+		withUser(t, "user1", func(userDB *sqlutils.SQLRunner) {
+			userDB.Exec(t,
+				fmt.Sprintf("ALTER CHANGEFEED %d ADD table_b, table_c set sink='external://second'", jobID),
+			)
+		})
+		rootDB.Exec(t, "SET CLUSTER SETTING changefeed.permissions.require_external_connection_sink = false")
+	})
+
+	// TODO(#94757): remove CONTROLCHANGEFEED entirely
+	t.Run("using-controlchangefeed-roleoption", func(t *testing.T) {
+		rootDB.Exec(t, `CREATE USER user2 WITH CONTROLCHANGEFEED`)
+		rootDB.Exec(t, `GRANT CHANGEFEED ON table_a TO user2`)
+		rootDB.Exec(t, `GRANT SELECT ON table_a TO user2`)
+
+		var jobID int
+		withUser(t, "feedCreator", func(userDB *sqlutils.SQLRunner) {
+			row := userDB.QueryRow(t, "CREATE CHANGEFEED for table_a INTO 'kafka://foo'")
+			row.Scan(&jobID)
+			userDB.Exec(t, `PAUSE JOB $1`, jobID)
+			waitForJobStatus(userDB, t, catpb.JobID(jobID), `paused`)
+		})
+
+		// user2 is missing the SELECT privilege on table_b and table_c.
+		withUser(t, "user2", func(userDB *sqlutils.SQLRunner) {
+			userDB.ExpectErr(t,
+				"pq: user user2 with CONTROLCHANGEFEED role option requires the SELECT privilege on all target tables to be able to run an enterprise changefeed",
+				fmt.Sprintf("ALTER CHANGEFEED %d ADD table_b, table_c set sink='kafka://bar'", jobID),
+			)
+		})
+		rootDB.Exec(t, `GRANT SELECT ON table_b TO user2`)
+		withUser(t, "user2", func(userDB *sqlutils.SQLRunner) {
+			userDB.ExpectErr(t,
+				"pq: user user2 with CONTROLCHANGEFEED role option requires the SELECT privilege on all target tables to be able to run an enterprise changefeed",
+				fmt.Sprintf("ALTER CHANGEFEED %d ADD table_b, table_c set sink='kafka://bar'", jobID),
+			)
+		})
+		rootDB.Exec(t, `GRANT SELECT ON table_c TO user2`)
+		withUser(t, "user2", func(userDB *sqlutils.SQLRunner) {
+			userDB.Exec(t,
+				fmt.Sprintf("ALTER CHANGEFEED %d ADD table_b, table_c set sink='kafka://bar'", jobID),
+			)
+		})
+	})
+}
+
 func TestAlterChangefeedAddTarget(t *testing.T) {
 	defer leaktest.AfterTest(t)()
 	defer log.Scope(t).Close(t)
@@ -1419,3 +1574,73 @@ func TestAlterChangefeedWithOldCursorFromCreateChangefeed(t *testing.T) {
 
 	cdcTest(t, testFn, feedTestEnterpriseSinks)
 }
+
+// TestChangefeedJobControl tests if a user can modify and existing changefeed
+// based on their privileges.
+func TestAlterChangefeedAccessControl(t *testing.T) {
+	defer leaktest.AfterTest(t)()
+	defer log.Scope(t).Close(t)
+
+	testFn := func(t *testing.T, s TestServer, f cdctest.TestFeedFactory) {
+		ChangefeedJobPermissionsTestSetup(t, s)
+		rootDB := sqlutils.MakeSQLRunner(s.DB)
+
+		createFeed := func(stmt string) (cdctest.EnterpriseTestFeed, func()) {
+			successfulFeed := feed(t, f, stmt)
+			closeCf := func() {
+				closeFeed(t, successfulFeed)
+			}
+			_, err := successfulFeed.Next()
+			require.NoError(t, err)
+			return successfulFeed.(cdctest.EnterpriseTestFeed), closeCf
+		}
+
+		// Create a changefeed and pause it.
+		var currentFeed cdctest.EnterpriseTestFeed
+		var closeCf func()
+		asUser(t, f, `feedCreator`, func(_ *sqlutils.SQLRunner) {
+			currentFeed, closeCf = createFeed(`CREATE CHANGEFEED FOR table_a, table_b`)
+		})
+		rootDB.Exec(t, "PAUSE job $1", currentFeed.JobID())
+		waitForJobStatus(rootDB, t, currentFeed.JobID(), `paused`)
+
+		// Verify who can modify the existing changefeed.
+		asUser(t, f, `userWithAllGrants`, func(userDB *sqlutils.SQLRunner) {
+			userDB.Exec(t, fmt.Sprintf(`ALTER CHANGEFEED %d DROP table_b`, currentFeed.JobID()))
+		})
+		asUser(t, f, `adminUser`, func(userDB *sqlutils.SQLRunner) {
+			userDB.Exec(t, fmt.Sprintf(`ALTER CHANGEFEED %d ADD table_b`, currentFeed.JobID()))
+		})
+		// jobController can access the job, but will hit an error re-creating the changefeed.
+		asUser(t, f, `jobController`, func(userDB *sqlutils.SQLRunner) {
+			userDB.ExpectErr(t, "pq: user jobcontroller requires the CHANGEFEED privilege on all target tables to be able to run an enterprise changefeed", fmt.Sprintf(`ALTER CHANGEFEED %d DROP table_b`, currentFeed.JobID()))
+		})
+		asUser(t, f, `userWithSomeGrants`, func(userDB *sqlutils.SQLRunner) {
+			userDB.ExpectErr(t, "pq: user userwithsomegrants does not have CHANGEFEED privilege on relation table_b", fmt.Sprintf(`ALTER CHANGEFEED %d ADD table_b`, currentFeed.JobID()))
+		})
+		asUser(t, f, `regularUser`, func(userDB *sqlutils.SQLRunner) {
+			userDB.ExpectErr(t, "pq: user regularuser does not have CHANGEFEED privilege on relation (table_a|table_b)", fmt.Sprintf(`ALTER CHANGEFEED %d ADD table_b`, currentFeed.JobID()))
+		})
+		closeCf()
+
+		// No one can modify changefeeds created by admins, except for admins.
+		// In this case, the root user creates the changefeed.
+		currentFeed, closeCf = createFeed(`CREATE CHANGEFEED FOR table_a, table_b`)
+		asUser(t, f, `adminUser`, func(userDB *sqlutils.SQLRunner) {
+			userDB.Exec(t, "PAUSE job $1", currentFeed.JobID())
+			require.NoError(t, currentFeed.WaitForStatus(func(s jobs.Status) bool {
+				return s == jobs.StatusPaused
+			}))
+		})
+		asUser(t, f, `userWithAllGrants`, func(userDB *sqlutils.SQLRunner) {
+			userDB.ExpectErr(t, "pq: only admins can control jobs owned by other admins", fmt.Sprintf(`ALTER CHANGEFEED %d ADD table_b`, currentFeed.JobID()))
+		})
+		asUser(t, f, `jobController`, func(userDB *sqlutils.SQLRunner) {
+			userDB.ExpectErr(t, "pq: only admins can control jobs owned by other admins", fmt.Sprintf(`ALTER CHANGEFEED %d ADD table_b`, currentFeed.JobID()))
+		})
+		closeCf()
+	}
+
+	// Only enterprise sinks create jobs.
+	cdcTest(t, testFn, feedTestEnterpriseSinks)
+}

pkg/ccl/changefeedccl/cdctest/BUILD.bazel

@@ -26,6 +26,7 @@ go_library(
         "//pkg/sql/catalog",
         "//pkg/sql/catalog/descs",
         "//pkg/sql/sem/tree",
+        "//pkg/testutils/sqlutils",
         "//pkg/util",
         "//pkg/util/fsm",
         "//pkg/util/hlc",

pkg/ccl/changefeedccl/cdctest/testfeed.go

@@ -13,6 +13,7 @@ import (
 
 	"github.com/cockroachdb/cockroach/pkg/jobs"
 	"github.com/cockroachdb/cockroach/pkg/jobs/jobspb"
+	"github.com/cockroachdb/cockroach/pkg/testutils/sqlutils"
 	"github.com/cockroachdb/cockroach/pkg/util/hlc"
 )
 
@@ -21,12 +22,11 @@ type TestFeedFactory interface {
 	// Feed creates a new TestFeed.
 	Feed(create string, args ...interface{}) (TestFeed, error)
 
-	// AsUser connects to the database as the specified user,
-	// calls fn(), then goes back to using the same root
-	// connection. Will return an error if the initial connection
-	// to the database fails, but fn is responsible for failing
-	// the test on other errors.
-	AsUser(user string, fn func()) error
+	// AsUser connects to the database as the specified user, calls fn() with the
+	// user's connection, then goes back to using the same root connection. Will
+	// return an error if the initial connection to the database fails, but fn is
+	// responsible for failing the test on other errors.
+	AsUser(user string, fn func(runner *sqlutils.SQLRunner)) error
 }
 
 // TestFeedMessage represents one row update or resolved timestamp message from