sql: add VIEWSYSTEMTABLE system privilege

This privilege is useful for support situations, where an engineer needs
to be able to view system tables without having full admin access.

Release note (sql change): Added the VIEWSYSTEMTABLE system privilege.
Users with this privilege have SELECT privileges for all tables in the
system database.

pkg/sql/authorization.go

@@ -262,14 +262,32 @@ func (p *planner) CheckPrivilegeForUser(
 	privilegeKind privilege.Kind,
 	user username.SQLUsername,
 ) error {
-	ok, err := p.HasPrivilege(ctx, privilegeObject, privilegeKind, user)
+	hasPriv, err := p.HasPrivilege(ctx, privilegeObject, privilegeKind, user)
 	if err != nil {
 		return err
 	}
-	if !ok {
-		return insufficientPrivilegeError(user, privilegeKind, privilegeObject)
+	if hasPriv {
+		return nil
 	}
-	return nil
+	// Special case for system tables. The VIEWSYSTEMTABLE system privilege is
+	// equivalent to having SELECT on all system tables. This is because it is not
+	// possible to dybamically grant SELECT privileges system tables, but in the
+	// context of support escalations, we need to be able to grant the ability to
+	// view system tables without granting the entire admin role.
+	if d, ok := privilegeObject.(catalog.Descriptor); ok {
+		if catalog.IsSystemDescriptor(d) && privilegeKind == privilege.SELECT {
+			hasViewSystemTablePriv, err := p.HasPrivilege(
+				ctx, syntheticprivilege.GlobalPrivilegeObject, privilege.VIEWSYSTEMTABLE, user,
+			)
+			if err != nil {
+				return err
+			}
+			if hasViewSystemTablePriv {
+				return nil
+			}
+		}
+	}
+	return insufficientPrivilegeError(user, privilegeKind, privilegeObject)
 }
 
 // CheckPrivilege implements the AuthorizationAccessor interface.

pkg/sql/logictest/testdata/logic_test/synthetic_privileges

@@ -397,3 +397,29 @@ statement ok
 REVOKE SYSTEM ALL FROM testuser
 
 subtest end
+
+subtest view_system_table
+
+user testuser
+
+# Make sure testuser does not have privileges first.
+statement error user testuser does not have SELECT privilege on relation users
+SELECT * FROM system.users WHERE username = 'testuser'
+
+user root
+
+statement ok
+GRANT SYSTEM VIEWSYSTEMTABLE TO testuser
+
+user testuser
+
+query TT
+SELECT username, "hashedPassword" FROM system.users WHERE username = 'testuser'
+----
+testuser  NULL
+
+# testuser still should not have write privileges.
+statement error user testuser does not have INSERT privilege on relation users
+INSERT INTO system.users VALUES ('cat', null, true, 200)
+
+subtest end

pkg/sql/privilege/privilege.go

@@ -71,6 +71,7 @@ const (
 	MODIFYSQLCLUSTERSETTING  Kind = 28
 	REPLICATION              Kind = 29
 	MANAGETENANT             Kind = 30
+	VIEWSYSTEMTABLE          Kind = 31
 )
 
 // Privilege represents a privilege parsed from an Access Privilege Inquiry
@@ -149,8 +150,12 @@ var (
 	// before v22.2 we treated Sequences the same as Tables. This is to avoid making
 	// certain privileges unavailable after upgrade migration.
 	// Note that "CREATE, CHANGEFEED, INSERT, DELETE, ZONECONFIG" are no-op privileges on sequences.
-	SequencePrivileges           = List{ALL, USAGE, SELECT, UPDATE, CREATE, CHANGEFEED, DROP, INSERT, DELETE, ZONECONFIG}
-	GlobalPrivileges             = List{ALL, BACKUP, RESTORE, MODIFYCLUSTERSETTING, EXTERNALCONNECTION, VIEWACTIVITY, VIEWACTIVITYREDACTED, VIEWCLUSTERSETTING, CANCELQUERY, NOSQLLOGIN, VIEWCLUSTERMETADATA, VIEWDEBUG, EXTERNALIOIMPLICITACCESS, VIEWJOB, MODIFYSQLCLUSTERSETTING, REPLICATION, MANAGETENANT}
+	SequencePrivileges = List{ALL, USAGE, SELECT, UPDATE, CREATE, CHANGEFEED, DROP, INSERT, DELETE, ZONECONFIG}
+	GlobalPrivileges   = List{
+		ALL, BACKUP, RESTORE, MODIFYCLUSTERSETTING, EXTERNALCONNECTION, VIEWACTIVITY, VIEWACTIVITYREDACTED,
+		VIEWCLUSTERSETTING, CANCELQUERY, NOSQLLOGIN, VIEWCLUSTERMETADATA, VIEWDEBUG, EXTERNALIOIMPLICITACCESS, VIEWJOB,
+		MODIFYSQLCLUSTERSETTING, REPLICATION, MANAGETENANT, VIEWSYSTEMTABLE,
+	}
 	VirtualTablePrivileges       = List{ALL, SELECT}
 	ExternalConnectionPrivileges = List{ALL, USAGE, DROP}
 )
@@ -196,6 +201,7 @@ var ByName = map[string]Kind{
 	"MODIFYSQLCLUSTERSETTING":  MODIFYSQLCLUSTERSETTING,
 	"REPLICATION":              REPLICATION,
 	"MANAGETENANT":             MANAGETENANT,
+	"VIEWSYSTEMTABLE":          VIEWSYSTEMTABLE,
 }
 
 // List is a list of privileges.