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https://github.com/isc-projects/bind9.git
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c1ba80169c
Make the maximum number of processed delegation nameservers configurable via the new 'max-delegation-servers' option (default: 13), replacing the hardcoded NS_PROCESSING_LIMIT (20). The default is reduced to 13 to precisely match the maximum number of root servers that can fit into a classic 512-byte UDP payload. This provides a natural, historically sound cap that mitigates resource exhaustion and amplification attacks from artificially inflated or misconfigured delegations. The configuration option is strictly bounded between 1 and 100 to ensure resolver stability.
122 lines
3.8 KiB
Python
122 lines
3.8 KiB
Python
# Copyright (C) Internet Systems Consortium, Inc. ("ISC")
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#
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# SPDX-License-Identifier: MPL-2.0
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#
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# This Source Code Form is subject to the terms of the Mozilla Public
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# License, v. 2.0. If a copy of the MPL was not distributed with this
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# file, you can obtain one at https://mozilla.org/MPL/2.0/.
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#
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# See the COPYRIGHT file distributed with this work for additional
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# information regarding copyright ownership.
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import os
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import isctest
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import isctest.mark
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pytestmark = [isctest.mark.with_dnstap]
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def line_to_ips_and_queries(line):
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# dnstap-read output line example
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# 05-Feb-2026 11:00:57.853 RQ 10.53.0.4:38507 -> 10.53.0.3:22047 TCP 56b sub.example.tld/IN/NS
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_, _, _, _, _, dst, _, _, query = line.split(" ", 9)
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ip, _ = dst.split(":", 1)
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return (ip, query)
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def extract_dnstap(ns, expectedlen):
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ns.rndc("dnstap -roll 1")
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path = os.path.join(ns.identifier, "dnstap.out.0")
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dnstapread = isctest.run.cmd(
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[isctest.vars.ALL["DNSTAPREAD"], path],
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)
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lines = dnstapread.out.splitlines()
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assert expectedlen == len(lines)
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return map(line_to_ips_and_queries, lines)
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def expect_query(expected_query, expected_query_count, ips_and_queries):
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count = 0
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for _, query in ips_and_queries:
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if query == expected_query:
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count += 1
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assert count == expected_query_count
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def expect_next_ip_and_query(expected_ips_and_queries, ips_and_queries):
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for expected_ip, expected_query in expected_ips_and_queries:
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ip, query = next(ips_and_queries)
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assert ip == expected_ip
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assert query == expected_query
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def check_nsprocessinglimit(ns, queries_count):
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msg = isctest.query.create("a.sub.example.tld.", "A")
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res = isctest.query.tcp(msg, ns.ip)
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isctest.check.servfail(res)
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# The 4 formers lines are request to find sub.example.tld NSs.
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# The latest are queries to sub.example.tld NSs.
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ips_and_queries = extract_dnstap(ns, queries_count)
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# Checking the begining of the resulution
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expect_next_ip_and_query(
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[
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("10.53.0.1", "./IN/NS"),
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("10.53.0.1", "tld/IN/NS"),
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("10.53.0.2", "example.tld/IN/NS"),
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("10.53.0.3", "sub.example.tld/IN/NS"),
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],
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ips_and_queries,
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)
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expect_query("a.sub.example.tld/IN/A", queries_count - 4, ips_and_queries)
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def test_nsprocessinglimit_default(ns4):
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check_nsprocessinglimit(ns4, 17)
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def reconfig_maxdelegationservers(ns, templates, count):
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templates.render(
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"ns4/named.conf", {"maxdelegationservers": f"max-delegation-servers {count};"}
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)
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with ns.watch_log_from_here() as watcher:
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ns.rndc("flush")
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ns.rndc("reload")
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watcher.wait_for_line("running")
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def reconfig_maxdelegationservers_failure(ns, templates, count):
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templates.render(
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"ns4/named.conf", {"maxdelegationservers": f"max-delegation-servers {count};"}
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)
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with ns.watch_log_from_here() as watcher:
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# Reload will fail, so do not raise the exception so the config line
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# can be checked.
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ns.rndc("reload", raise_on_exception=False)
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watcher.wait_for_line("reloading configuration failed: out of range")
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def test_nsprocessinglimit_13ns(ns4, templates):
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reconfig_maxdelegationservers(ns4, templates, 13)
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check_nsprocessinglimit(ns4, 17)
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def test_nsprocessinglimit_5ns(ns4, templates):
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reconfig_maxdelegationservers(ns4, templates, 5)
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check_nsprocessinglimit(ns4, 9)
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def test_nsprocessinglimit_20ns(ns4, templates):
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reconfig_maxdelegationservers(ns4, templates, 20)
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check_nsprocessinglimit(ns4, 24)
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def test_nsprocessinglimit_lower(ns4, templates):
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reconfig_maxdelegationservers_failure(ns4, templates, 0)
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def test_nsprocessinglimit_upper(ns4, templates):
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reconfig_maxdelegationservers_failure(ns4, templates, 101)
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