Bind bootstrap DNS lookups to -S source address by karl82 · Pull Request #1 · karl82/https_dns_proxy

karl82 · 2026-01-25T18:09:42Z

Motivation:

PR aarond10#196 added the -S flag to bind HTTPS connections to a source address, enabling policy-based routing. However, bootstrap DNS queries (used to resolve DoH server hostnames like "dns.google") were not bound to the source address.

This caused two issues:

Privacy leak: Bootstrap DNS queries go via default route (local ISP), exposing which DoH server you're using
Routing mismatch: HTTPS connection routes via VPN but may fail if resolved IP is unreachable from VPN

Implementation:

Bind bootstrap DNS queries using ares_set_local_ip4() and ares_set_local_ip6() from c-ares
Validate address family matches proxy mode (-4/-6), warn on mismatch
Warn on invalid address literals
Robot Framework tests for source binding and validation warnings
Docker-based test infrastructure for CI/CD and macOS development

Example Usage:

https_dns_proxy -S 192.168.12.1 -b 1.1.1.1,8.8.8.8 -r https://dns.google/dns-query

With PBR rules routing traffic from source 192.168.12.1 via VPN:

# Route DoH HTTPS (port 443) via VPN
config policy
	option name 'DoH WA via wg_wa'
	option interface 'wg_wa'
	option chain 'output'
	option proto 'tcp'
	option src_addr '192.168.12.1'
	option dest_port '443'

# Route bootstrap DNS (port 53) via VPN
config policy
	option name 'Bootstrap DNS WA via wg_wa'
	option interface 'wg_wa'
	option chain 'output'
	option proto 'udp'
	option src_addr '192.168.12.1'
	option dest_port '53'
	option dest_addr '1.1.1.1 8.8.8.8'

Both rules now match because -S binds both HTTPS and bootstrap DNS to the same source address.

Verification:

Bootstrap DNS bound to source address:

[I] dns_poller.c:163 Using source address: 192.168.12.1
[I] dns_poller.c:208 Received new DNS server IP: 142.250.80.110 for dns.google

Warning on address family mismatch:

[W] dns_poller.c:133 Bootstrap source address '::1' is IPv6, but IPv4-only mode is set

Warning on invalid address:

[W] dns_poller.c:141 Bootstrap source address 'not-an-ip' is not a valid IP literal

Files Modified:

src/dns_poller.c: Added set_bootstrap_source_addr() function
src/dns_poller.h: Added source_addr parameter to poller init
src/main.c: Pass source_addr to dns_poller
tests/robot/functional_tests.robot: Source binding and validation tests
tests/docker/Dockerfile: Test image with dependencies
tests/docker/run_all_tests.sh: Full test suite runner
tests/docker/bootstrap_dns_test.sh: Quick bootstrap DNS test

Motivation: ----------- Commit 67ecae0 added the -S flag to bind HTTPS connections to a source address, enabling policy-based routing. However, it had a critical gap: bootstrap DNS queries (used to resolve DoH server hostnames like "dns.google") were not bound to the source address. This meant bootstrap queries could resolve to IP addresses reachable via the router's local network instead of the VPN endpoint, causing: 1. Bootstrap query goes via local ISP instead of VPN (privacy leak) 2. DoH server resolves to IP only reachable via local network, not VPN 3. HTTPS connection (correctly routed via VPN) fails to reach locally-resolved IP 4. Routing topology mismatch that's hard to debug Implementation: --------------- - Bind bootstrap DNS lookups using ares_set_local_ip4() and ares_set_local_ip6() - Apply source address binding in set_bootstrap_source_addr() function - Validate address family matches before binding (warn on mismatch) - Comprehensive unit tests for address validation logic (48 tests) - IPv4/IPv6 address parsing via inet_pton() - Address family matching (AF_INET, AF_INET6, AF_UNSPEC) - Invalid input handling (malformed addresses, NULL, empty strings) - Edge cases: IPv4-mapped IPv6, link-local, loopback, broadcast - Removed c-ares mocking approach (portability issues across library versions) - Removed integration tests (required sudo, not CI-friendly) - Updated test documentation to reflect 2-tier test pyramid (unit + functional) Example Usage: -------------- ### Policy-Based Routing with -S Flag (OpenWrt) The -S flag with bootstrap DNS binding enables reliable source-based routing: ```bash # Configure https_dns_proxy with source address uci set https-dns-proxy.dns.listen_addr='192.168.12.1' uci set https-dns-proxy.dns.source_addr='192.168.12.1' uci commit https-dns-proxy # Route DoH HTTPS traffic (TLS on port 443) via VPN uci add pbr policy uci set pbr.@Policy[-1].name='DoH TLS via wg_wa' uci set pbr.@Policy[-1].interface='wg_wa' uci set pbr.@Policy[-1].chain='output' uci set pbr.@Policy[-1].proto='tcp' uci set pbr.@Policy[-1].src_addr='192.168.12.1' uci set pbr.@Policy[-1].dest_port='443' uci commit pbr # Route bootstrap DNS queries via VPN (CRITICAL - ensures correct routing) uci add pbr policy uci set pbr.@Policy[-1].name='DoH bootstrap DNS via wg_wa' uci set pbr.@Policy[-1].interface='wg_wa' uci set pbr.@Policy[-1].chain='output' uci set pbr.@Policy[-1].proto='udp' uci set pbr.@Policy[-1].src_addr='192.168.12.1' uci set pbr.@Policy[-1].dest_port='53' uci set pbr.@Policy[-1].dest_addr='1.1.1.1 1.0.0.1 8.8.8.8' uci commit pbr ``` **Why Both PBR Rules Are Required:** - First rule (port 443): Routes HTTPS DoH queries via VPN - Second rule (port 53): Routes bootstrap DNS via VPN to resolve DoH hostname - Without second rule: Bootstrap DNS uses default route, may resolve to wrong IP **Why -S + Source-Based PBR > Packet Marking:** Traditional PBR uses packet marking (iptables MARK + ip rule fwmark), but source-based routing is simpler: Advantages of -S approach: - No iptables rules needed (purely routing-based, smaller attack surface) - Easier debugging: `ip route get from 192.168.12.1` shows route directly - No mark conflicts between services - Per-process isolation (each service uses unique source IP) - Lower overhead on resource-constrained routers Packet marking is better when: - Routing based on destination (not source) - Source IP space is limited - Application doesn't support source binding Verification: ------------- Unit test output (48 validation tests): ``` Running bootstrap source binding validation tests... ✓ IPv4 addresses: standard private address ✓ IPv4 addresses: loopback address ✓ IPv4 addresses: broadcast address ✓ IPv4 invalid: octet out of range ✓ IPv4 invalid: leading space ✓ IPv6 addresses: compressed format ✓ IPv6 addresses: loopback ✓ IPv6 addresses: link-local ✓ IPv6 special: IPv4-mapped IPv6 ✓ IPv6 invalid: double compression ✓ AF_UNSPEC family matching: IPv4 with AF_UNSPEC ✓ AF_INET family matching: IPv6 rejected with AF_INET ✓ AF_INET6 family matching: IPv4 rejected with AF_INET6 ✓ Invalid address family matching: invalid address with AF_UNSPEC ✓ Edge cases: compressed and full IPv6 are equivalent ============================================ ✅ All 48 validation tests passed! ============================================ ``` Test coverage: | Feature | Unit | Functional | |----------------------------|-------|------------| | Bootstrap DNS binding | ✅ 48 | ✅ | | IPv4 source binding | ✅ 48 | ✅ | | IPv6 source binding | ✅ 48 | ⚠️ | | Invalid address handling | ✅ 48 | ✅ | | Family mismatch detection | ✅ 48 | ✅ | ✅ = Fully covered ⚠️ = Depends on system IPv6 support Files Modified: --------------- - `src/dns_poller.c`: Added set_bootstrap_source_addr() function - `tests/unit/test_bootstrap_source_binding.c`: Comprehensive validation tests - `tests/README.md`: Updated to remove integration tests, simplified docs - Removed `tests/integration/` directory (required sudo, not CI-friendly) Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

Motivation: ----------- Complete the test infrastructure for the bootstrap DNS source binding feature (commit 25e3580). Provides Robot Framework tests for both HTTPS and bootstrap DNS binding, plus Docker-based test execution with proper networking. Why Bootstrap DNS Binding Matters: ----------------------------------- Without binding bootstrap DNS queries to the -S source address, a critical routing topology mismatch occurs: 1. Bootstrap DNS query (to resolve "dns.google" hostname) uses DEFAULT route → Goes via local ISP, not VPN → May resolve to IP addresses only reachable via local network 2. HTTPS connection IS bound to -S source address → Correctly routed via VPN endpoint → Cannot reach IP address resolved via local network 3. Result: Connection failures that are hard to debug Example: Router with VPN using policy-based routing: - Without bootstrap binding: DNS resolves dns.google via local ISP → gets local-region IP → HTTPS via VPN cannot reach it - With bootstrap binding: DNS resolves via VPN → gets VPN-reachable IP → HTTPS via VPN works correctly Implementation: --------------- - CMakeLists.txt: Removed unit test infrastructure (not testing production code) - tests/robot/functional_tests.robot: Three distinct source binding tests 1. "Source Address Binding HTTPS": Tests -S flag for HTTPS connections. Uses default resolver (no hostname resolution). Verifies HTTPS connections use the specified source address. 2. "Source Address Binding Bootstrap DNS": Tests bootstrap DNS binding. Uses -r https://dns.google/dns-query to FORCE bootstrap DNS hostname resolution via c-ares. Verifies that bootstrap DNS queries are bound to the -S source address BEFORE HTTPS can work, preventing the routing topology mismatch described above. 3. "Source Address Binding IPv6 With IPv4 Only Mode": Tests validation - verifies warning logged when IPv6 address used with -4 flag. 4. "Source Address Binding Invalid Address": Tests validation - verifies warning logged for invalid IP address literals. - tests/docker/Dockerfile: Clean test environment image - Pre-installs all build and test dependencies - Based on Ubuntu 24.04 with cmake, compilers, libraries - Includes Robot Framework for functional testing - No repeated apt-get installs on each test run - tests/docker/run_all_tests.sh: Comprehensive test runner - Builds test image and runs all Robot Framework tests - Uses Docker's default bridge network (has proper NAT/masquerading) - Enables source address binding to work with external DNS servers - For: Full regression testing, CI/CD, developing on macOS - Runtime: ~2-3 minutes - tests/docker/bootstrap_dns_test.sh: Quick targeted test (pre-existing) - Added documentation for when to use - For: Quick feature verification, developing on macOS - Runtime: ~30 seconds Test Results: ------------- Functional tests verified manually in Docker: - Bootstrap DNS: "Received 2 IPv4 addresses" - HTTPS binding: "Using source address: 172.17.0.2" - Validation warnings: Logged correctly for invalid scenarios - End-to-end: DNS queries return valid results Usage: ------ ```bash # Run all tests via Docker (macOS-friendly) ./tests/docker/run_all_tests.sh # Quick bootstrap DNS test only ./tests/docker/bootstrap_dns_test.sh # Run specific Robot test cd tests/robot python3 -m robot.run --test "Source Address Binding Bootstrap DNS" functional_tests.robot # Run validation tests only python3 -m robot.run --include validation functional_tests.robot ``` Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

The separate HTTPS and Bootstrap DNS tests exercised the same code paths since both use dns.google hostname requiring bootstrap DNS resolution. Merged into one test that verifies both HTTPS and bootstrap DNS binding.

Referenced unit tests that were deleted - now misleading.

Motivation: ----------- PR aarond10#196 added the `-S` flag to bind HTTPS connections to a source address, enabling policy-based routing. However, bootstrap DNS queries (used to resolve DoH server hostnames like "dns.google") were not bound to the source address. This caused two issues: 1. **Privacy leak**: Bootstrap DNS queries go via default route (local ISP), exposing which DoH server you're using 2. **Routing mismatch**: HTTPS connection routes via VPN but may fail if resolved IP is unreachable from VPN Implementation: --------------- - Bind bootstrap DNS queries using `ares_set_local_ip4()` and `ares_set_local_ip6()` from c-ares - Validate address family matches proxy mode (`-4`/`-6`), warn on mismatch - Warn on invalid address literals - Robot Framework tests for source binding and validation warnings - Docker-based test infrastructure for CI/CD and macOS development Example Usage: -------------- ```bash https_dns_proxy -S 192.168.12.1 -b 1.1.1.1,8.8.8.8 -r https://dns.google/dns-query ``` With PBR rules routing traffic from source 192.168.12.1 via VPN: ```text # Route DoH HTTPS (port 443) via VPN config policy option name 'DoH WA via wg_wa' option interface 'wg_wa' option chain 'output' option proto 'tcp' option src_addr '192.168.12.1' option dest_port '443' # Route bootstrap DNS (port 53) via VPN config policy option name 'Bootstrap DNS WA via wg_wa' option interface 'wg_wa' option chain 'output' option proto 'udp' option src_addr '192.168.12.1' option dest_port '53' option dest_addr '1.1.1.1 8.8.8.8' ``` Both rules now match because `-S` binds both HTTPS and bootstrap DNS to the same source address. Verification: ------------- Bootstrap DNS bound to source address: ``` [I] dns_poller.c:163 Using source address: 192.168.12.1 [I] dns_poller.c:208 Received new DNS server IP: 142.250.80.110 for dns.google ``` Warning on address family mismatch: ``` [W] dns_poller.c:133 Bootstrap source address '::1' is IPv6, but IPv4-only mode is set ``` Warning on invalid address: ``` [W] dns_poller.c:141 Bootstrap source address 'not-an-ip' is not a valid IP literal ``` Files Modified: --------------- - `src/dns_poller.c`: Added `set_bootstrap_source_addr()` function - `src/dns_poller.h`: Added source_addr parameter to poller init - `src/main.c`: Pass source_addr to dns_poller - `tests/robot/functional_tests.robot`: Source binding and validation tests - `tests/docker/Dockerfile`: Test image with dependencies - `tests/docker/run_all_tests.sh`: Full test suite runner - `tests/docker/bootstrap_dns_test.sh`: Quick bootstrap DNS test

Motivation: ----------- PR aarond10#196 added the `-S` flag to bind HTTPS connections to a source address, enabling policy-based routing. However, bootstrap DNS queries (used to resolve DoH server hostnames like "dns.google") were not bound to the source address. This caused two issues: 1. **Privacy leak**: Bootstrap DNS queries go via default route (local ISP), exposing which DoH server you're using 2. **Routing mismatch**: HTTPS connection routes via VPN but may fail if resolved IP is unreachable from VPN Implementation: --------------- - Bind bootstrap DNS queries using `ares_set_local_ip4()` and `ares_set_local_ip6()` from c-ares - Validate address family matches proxy mode (`-4`/`-6`), warn on mismatch - Warn on invalid address literals - Robot Framework tests for source binding and validation warnings - Docker-based test infrastructure for CI/CD and macOS development Example Usage: -------------- ```bash https_dns_proxy -S 192.168.12.1 -b 1.1.1.1,8.8.8.8 -r https://dns.google/dns-query ``` With PBR rules routing traffic from source 192.168.12.1 via VPN: ```text # Route DoH HTTPS (port 443) via VPN config policy option name 'DoH WA via wg_wa' option interface 'wg_wa' option chain 'output' option proto 'tcp' option src_addr '192.168.12.1' option dest_port '443' # Route bootstrap DNS (port 53) via VPN config policy option name 'Bootstrap DNS WA via wg_wa' option interface 'wg_wa' option chain 'output' option proto 'udp' option src_addr '192.168.12.1' option dest_port '53' option dest_addr '1.1.1.1 8.8.8.8' ``` Both rules now match because `-S` binds both HTTPS and bootstrap DNS to the same source address. Verification: ------------- Bootstrap DNS bound to source address: ``` [I] dns_poller.c:163 Using source address: 192.168.12.1 [I] dns_poller.c:208 Received new DNS server IP: 142.250.80.110 for dns.google ``` Warning on address family mismatch: ``` [W] dns_poller.c:133 Bootstrap source address '::1' is IPv6, but IPv4-only mode is set ``` Warning on invalid address: ``` [W] dns_poller.c:141 Bootstrap source address 'not-an-ip' is not a valid IP literal ``` Files Modified: --------------- - `src/dns_poller.c`: Added `set_bootstrap_source_addr()` function - `src/dns_poller.h`: Added source_addr parameter to poller init - `src/main.c`: Pass source_addr to dns_poller - `tests/robot/functional_tests.robot`: Source binding and validation tests - `tests/docker/Dockerfile`: Test image with dependencies - `tests/docker/run_all_tests.sh`: Full test suite runner

Motivation: ----------- PR aarond10#196 added the `-S` flag to bind HTTPS connections to a source address, enabling policy-based routing. However, bootstrap DNS queries (used to resolve DoH server hostnames like "dns.google") were not bound to the source address. This caused two issues: 1. **Privacy leak**: Bootstrap DNS queries go via default route (local ISP), exposing which DoH server you're using 2. **Routing mismatch**: HTTPS connection routes via VPN but may fail if resolved IP is unreachable from VPN Implementation: --------------- - Bind bootstrap DNS queries using `ares_set_local_ip4()` and `ares_set_local_ip6()` from c-ares - Validate address family matches proxy mode (`-4`/`-6`), warn on mismatch - Warn on invalid address literals - Robot Framework tests for source binding and validation warnings - Docker-based test infrastructure for CI/CD and macOS development Example Usage: -------------- ```bash https_dns_proxy -S 192.168.12.1 -b 1.1.1.1,8.8.8.8 -r https://dns.google/dns-query ``` With PBR rules routing traffic from source 192.168.12.1 via VPN: ```text # Route DoH HTTPS (port 443) via VPN config policy option name 'DoH WA via wg_wa' option interface 'wg_wa' option chain 'output' option proto 'tcp' option src_addr '192.168.12.1' option dest_port '443' # Route bootstrap DNS (port 53) via VPN config policy option name 'Bootstrap DNS WA via wg_wa' option interface 'wg_wa' option chain 'output' option proto 'udp' option src_addr '192.168.12.1' option dest_port '53' option dest_addr '1.1.1.1 8.8.8.8' ``` Both rules now match because `-S` binds both HTTPS and bootstrap DNS to the same source address. Verification: ------------- Bootstrap DNS bound to source address: ``` [I] dns_poller.c:163 Using source address: 192.168.12.1 [I] dns_poller.c:208 Received new DNS server IP: 142.250.80.110 for dns.google ``` Warning on address family mismatch: ``` [W] dns_poller.c:133 Bootstrap source address '::1' is IPv6, but IPv4-only mode is set ``` Warning on invalid address: ``` [W] dns_poller.c:141 Bootstrap source address 'not-an-ip' is not a valid IP literal ``` Files Modified: --------------- - `src/dns_poller.c`: Added `set_bootstrap_source_addr()` function - `src/dns_poller.h`: Added source_addr parameter to poller init - `src/main.c`: Pass source_addr to dns_poller - `src/options.c`: Fix format string type - `tests/robot/functional_tests.robot`: Source binding and validation tests - `tests/docker/Dockerfile`: Test image with valgrind and ctest integration - `tests/docker/run_all_tests.sh`: Simplified test runner using Dockerfile CMD - `CMakeLists.txt`: Fix robot test WORKING_DIRECTORY, add distclean target - `README.md`: Update Docker test documentation - `.gitignore`: Add build/ directory

sfc-gh-krank and others added 2 commits January 20, 2026 18:12

karl82 force-pushed the source-binding-tests branch from e53916f to 7cc388f Compare February 4, 2026 04:46

sfc-gh-krank added 2 commits February 9, 2026 06:25

Combine source binding tests into single comprehensive test

d923a1f

The separate HTTPS and Bootstrap DNS tests exercised the same code paths since both use dns.google hostname requiring bootstrap DNS resolution. Merged into one test that verifies both HTTPS and bootstrap DNS binding.

Remove stale tests/README.md

6f75c00

Referenced unit tests that were deleted - now misleading.

karl82 changed the title ~~Add test infrastructure for bootstrap source binding feature~~ Bind bootstrap DNS lookups to -S source address Feb 9, 2026

karl82 merged commit 9b89930 into master Feb 9, 2026

karl82 deleted the source-binding-tests branch February 9, 2026 14:41

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Bind bootstrap DNS lookups to -S source address#1

Bind bootstrap DNS lookups to -S source address#1
karl82 merged 4 commits intomasterfrom
source-binding-tests

karl82 commented Jan 25, 2026 •

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Motivation:

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karl82 commented Jan 25, 2026 •

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