algo/tests/test_cloud_init_template.py
Dan Guido f668af22d0
Fix VPN routing on multi-homed systems by specifying output interface (#14826)
* Fix VPN routing by adding output interface to NAT rules

The NAT rules were missing the output interface specification (-o eth0),
which caused routing failures on multi-homed systems (servers with multiple
network interfaces). Without specifying the output interface, packets might
not be NAT'd correctly.

Changes:
- Added -o {{ ansible_default_ipv4['interface'] }} to all NAT rules
- Updated both IPv4 and IPv6 templates
- Updated tests to verify output interface is present
- Added ansible_default_ipv4/ipv6 to test fixtures

This fixes the issue where VPN clients could connect but not route traffic
to the internet on servers with multiple network interfaces (like DigitalOcean
droplets with private networking enabled).

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <noreply@anthropic.com>

* Fix VPN routing by adding output interface to NAT rules

On multi-homed systems (servers with multiple network interfaces or multiple IPs
on one interface), MASQUERADE rules need to specify which interface to use for
NAT. Without the output interface specification, packets may not be routed correctly.

This fix adds the output interface to all NAT rules:
  -A POSTROUTING -s [vpn_subnet] -o eth0 -j MASQUERADE

Changes:
- Modified roles/common/templates/rules.v4.j2 to include output interface
- Modified roles/common/templates/rules.v6.j2 for IPv6 support
- Added tests to verify output interface is present in NAT rules
- Added ansible_default_ipv4/ipv6 variables to test fixtures

For deployments on providers like DigitalOcean where MASQUERADE still fails
due to multiple IPs on the same interface, users can enable the existing
alternative_ingress_ip option in config.cfg to use explicit SNAT.

Testing:
- Verified on live servers
- All unit tests pass (67/67)
- Mutation testing confirms test coverage

This fixes VPN connectivity on servers with multiple interfaces while
remaining backward compatible with single-interface deployments.

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <noreply@anthropic.com>

* Fix dnscrypt-proxy not listening on VPN service IPs

Problem: dnscrypt-proxy on Ubuntu uses systemd socket activation by default,
which overrides the configured listen_addresses in dnscrypt-proxy.toml.
The socket only listens on 127.0.2.1:53, preventing VPN clients from
resolving DNS queries through the configured service IPs.

Solution: Disable and mask the dnscrypt-proxy.socket unit to allow
dnscrypt-proxy to bind directly to the VPN service IPs specified in
its configuration file.

This fixes DNS resolution for VPN clients on Ubuntu 20.04+ systems.

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <noreply@anthropic.com>

* Apply Python linting and formatting

- Run ruff check --fix to fix linting issues
- Run ruff format to ensure consistent formatting
- All tests still pass after formatting changes

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <noreply@anthropic.com>

* Restrict DNS access to VPN clients only

Security fix: The firewall rule for DNS was accepting traffic from any
source (0.0.0.0/0) to the local DNS resolver. While the service IP is
on the loopback interface (which normally isn't routable externally),
this could be a security risk if misconfigured.

Changed firewall rules to only accept DNS traffic from VPN subnets:
- INPUT rule now includes -s {{ subnets }} to restrict source IPs
- Applied to both IPv4 and IPv6 rules
- Added test to verify DNS is properly restricted

This ensures the DNS resolver is only accessible to connected VPN
clients, not the entire internet.

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <noreply@anthropic.com>

* Fix dnscrypt-proxy service startup with masked socket

Problem: dnscrypt-proxy.service has a dependency on dnscrypt-proxy.socket
through the TriggeredBy directive. When we mask the socket before starting
the service, systemd fails with "Unit dnscrypt-proxy.socket is masked."

Solution:
1. Override the service to remove socket dependency (TriggeredBy=)
2. Reload systemd daemon immediately after override changes
3. Start the service (which now doesn't require the socket)
4. Only then disable and mask the socket

This ensures dnscrypt-proxy can bind directly to the configured IPs
without socket activation, while preventing the socket from being
re-enabled by package updates.

Changes:
- Added TriggeredBy= override to remove socket dependency
- Added explicit daemon reload after service overrides
- Moved socket masking to after service start in main.yml
- Fixed YAML formatting issues

Testing: Deployment now succeeds with dnscrypt-proxy binding to VPN IPs

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <noreply@anthropic.com>

* Fix dnscrypt-proxy by not masking the socket

Problem: Masking dnscrypt-proxy.socket prevents the service from starting
because the service has Requires=dnscrypt-proxy.socket dependency.

Solution: Simply stop and disable the socket without masking it. This
prevents socket activation while allowing the service to start and bind
directly to the configured IPs.

Changes:
- Removed socket masking (just disable it)
- Moved socket disabling before service start
- Removed invalid systemd directives from override

Testing: Confirmed dnscrypt-proxy now listens on VPN service IPs

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <noreply@anthropic.com>

* Use systemd socket activation properly for dnscrypt-proxy

Instead of fighting systemd socket activation, configure it to listen
on the correct VPN service IPs. This is more systemd-native and reliable.

Changes:
- Create socket override to listen on VPN IPs instead of localhost
- Clear default listeners and add VPN service IPs
- Use empty listen_addresses in dnscrypt-proxy.toml for socket activation
- Keep socket enabled and let systemd manage the activation
- Add handler for restarting socket when config changes

Benefits:
- Works WITH systemd instead of against it
- Survives package updates better
- No dependency conflicts
- More reliable service management

This approach is cleaner than disabling socket activation entirely and
ensures dnscrypt-proxy is accessible to VPN clients on the correct IPs.

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <noreply@anthropic.com>

* Document debugging lessons learned in CLAUDE.md

Added comprehensive debugging guidance based on our troubleshooting session:

- VPN connectivity troubleshooting order (DNS first!)
- systemd socket activation best practices
- Common deployment failures and solutions
- Time wasters to avoid (lessons learned the hard way)
- Multi-homed system considerations
- Testing notes for DigitalOcean

These additions will help future debugging sessions avoid the same
rabbit holes and focus on the most likely issues first.

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <noreply@anthropic.com>

* Fix DNS resolution for VPN clients by enabling route_localnet

The issue was that dnscrypt-proxy listens on a special loopback IP
(randomly generated in 172.16.0.0/12 range) which wasn't accessible
from VPN clients. This fix:

1. Enables net.ipv4.conf.all.route_localnet sysctl to allow routing
   to loopback IPs from other interfaces
2. Ensures dnscrypt-proxy socket is properly restarted when its
   configuration changes
3. Adds proper handler flushing after socket configuration updates

This allows VPN clients to reach the DNS resolver at the local_service_ip
address configured on the loopback interface.

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <noreply@anthropic.com>

* Improve security by using interface-specific route_localnet

Instead of enabling route_localnet globally (net.ipv4.conf.all.route_localnet),
this change enables it only on the specific interfaces that need it:
- WireGuard interface (wg0) for WireGuard VPN clients
- Main network interface (eth0/etc) for IPsec VPN clients

This minimizes the security impact by restricting loopback routing to only
the VPN interfaces, preventing other interfaces from being able to route
to loopback addresses.

The interface-specific approach provides the same functionality (allowing
VPN clients to reach the DNS resolver on the local_service_ip) while
reducing the potential attack surface.

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <noreply@anthropic.com>

* Revert to global route_localnet to fix deployment failure

The interface-specific route_localnet approach failed because:
- WireGuard interface (wg0) doesn't exist until the service starts
- We were trying to set the sysctl before the interface was created
- This caused deployment failures with "No such file or directory"

Reverting to the global setting (net.ipv4.conf.all.route_localnet=1) because:
- It always works regardless of interface creation timing
- VPN users are trusted (they have our credentials)
- Firewall rules still restrict access to only port 53
- The security benefit of interface-specific settings is minimal
- The added complexity isn't worth the marginal security improvement

This ensures reliable deployments while maintaining the DNS resolution fix.

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <noreply@anthropic.com>

* Fix dnscrypt-proxy socket restart and remove problematic BPF hardening

Two important fixes:

1. Fix dnscrypt-proxy socket not restarting with new configuration
   - The socket wasn't properly restarting when its override config changed
   - This caused DNS to listen on wrong IP (127.0.2.1 instead of local_service_ip)
   - Now directly restart the socket when configuration changes
   - Add explicit daemon reload before restarting

2. Remove BPF JIT hardening that causes deployment errors
   - The net.core.bpf_jit_enable sysctl isn't available on all kernels
   - It was causing "Invalid argument" errors during deployment
   - This was optional security hardening with minimal benefit
   - Removing it eliminates deployment errors for most users

These fixes ensure reliable DNS resolution for VPN clients and clean
deployments without error messages.

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <noreply@anthropic.com>

* Update CLAUDE.md with comprehensive debugging lessons learned

Based on our extensive debugging session, this update adds critical documentation:

## DNS Architecture and Troubleshooting
- Explained the local_service_ip design and why it requires route_localnet
- Added detailed DNS debugging methodology with exact steps in order
- Documented systemd socket activation complexities and common mistakes
- Added specific commands to verify DNS is working correctly

## Architectural Decisions
- Added new section explaining trade-offs in Algo's design choices
- Documented why local_service_ip uses loopback instead of alternatives
- Explained iptables-legacy vs iptables-nft backend choice

## Enhanced Debugging Guidance
- Expanded troubleshooting with exact commands and expected outputs
- Added warnings about configuration changes that need restarts
- Documented socket activation override requirements in detail
- Added common pitfalls like interface-specific sysctls

## Time Wasters Section
- Added new lessons learned from this debugging session
- Interface-specific route_localnet (fails before interface exists)
- DNAT for loopback addresses (doesn't work)
- BPF JIT hardening (causes errors on many kernels)

This documentation will help future maintainers avoid the same debugging
rabbit holes and understand why things are designed the way they are.

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <noreply@anthropic.com>

---------

Co-authored-by: Claude <noreply@anthropic.com>
2025-08-17 22:12:23 -04:00

260 lines
8.3 KiB
Python

#!/usr/bin/env python3
"""
Cloud-init template validation test.
This test validates that the cloud-init template for DigitalOcean deployments
renders correctly and produces valid YAML that cloud-init can parse.
This test helps prevent regressions like issue #14800 where YAML formatting
issues caused cloud-init to fail completely, resulting in SSH timeouts.
Usage:
python3 tests/test_cloud_init_template.py
Or from project root:
python3 -m pytest tests/test_cloud_init_template.py -v
"""
import sys
from pathlib import Path
import yaml
# Add project root to path for imports if needed
PROJECT_ROOT = Path(__file__).parent.parent
sys.path.insert(0, str(PROJECT_ROOT))
def create_expected_cloud_init():
"""
Create the expected cloud-init content that should be generated
by our template after the YAML indentation fix.
"""
return """#cloud-config
# CRITICAL: The above line MUST be exactly "#cloud-config" (no space after #)
# This is required by cloud-init's YAML parser. Adding a space breaks parsing
# and causes all cloud-init directives to be skipped, resulting in SSH timeouts.
# See: https://github.com/trailofbits/algo/issues/14800
output: {all: '| tee -a /var/log/cloud-init-output.log'}
package_update: true
package_upgrade: true
packages:
- sudo
users:
- default
- name: algo
homedir: /home/algo
sudo: ALL=(ALL) NOPASSWD:ALL
groups: adm,netdev
shell: /bin/bash
lock_passwd: true
ssh_authorized_keys:
- "ssh-rsa AAAAB3NzaC1yc2EAAAADAQABAAACAQDTest algo-test"
write_files:
- path: /etc/ssh/sshd_config
content: |
Port 4160
AllowGroups algo
PermitRootLogin no
PasswordAuthentication no
ChallengeResponseAuthentication no
UsePAM yes
X11Forwarding yes
PrintMotd no
AcceptEnv LANG LC_*
Subsystem sftp /usr/lib/openssh/sftp-server
runcmd:
- set -x
- ufw --force reset
- sudo apt-get remove -y --purge sshguard || true
- systemctl restart sshd.service
"""
class TestCloudInitTemplate:
"""Test class for cloud-init template validation."""
def test_yaml_validity(self):
"""Test that the expected cloud-init YAML is valid."""
print("🧪 Testing YAML validity...")
cloud_init_content = create_expected_cloud_init()
try:
parsed = yaml.safe_load(cloud_init_content)
print("✅ YAML parsing successful")
assert parsed is not None, "YAML should parse to a non-None value"
return parsed
except yaml.YAMLError as e:
print(f"❌ YAML parsing failed: {e}")
assert False, f"YAML parsing failed: {e}"
def test_required_sections(self):
"""Test that all required cloud-init sections are present."""
print("🧪 Testing required sections...")
parsed = self.test_yaml_validity()
required_sections = ["package_update", "package_upgrade", "packages", "users", "write_files", "runcmd"]
missing = [section for section in required_sections if section not in parsed]
assert not missing, f"Missing required sections: {missing}"
print("✅ All required sections present")
def test_ssh_configuration(self):
"""Test that SSH configuration is correct."""
print("🧪 Testing SSH configuration...")
parsed = self.test_yaml_validity()
write_files = parsed.get("write_files", [])
assert write_files, "write_files section should be present"
# Find sshd_config file
sshd_config = None
for file_entry in write_files:
if file_entry.get("path") == "/etc/ssh/sshd_config":
sshd_config = file_entry
break
assert sshd_config, "sshd_config file should be in write_files"
content = sshd_config.get("content", "")
assert content, "sshd_config should have content"
# Check required SSH configurations
required_configs = ["Port 4160", "AllowGroups algo", "PermitRootLogin no", "PasswordAuthentication no"]
missing = [config for config in required_configs if config not in content]
assert not missing, f"Missing SSH configurations: {missing}"
# Verify proper formatting - first line should be Port directive
lines = content.strip().split("\n")
assert lines[0].strip() == "Port 4160", f"First line should be 'Port 4160', got: {repr(lines[0])}"
print("✅ SSH configuration correct")
def test_user_creation(self):
"""Test that algo user will be created correctly."""
print("🧪 Testing user creation...")
parsed = self.test_yaml_validity()
users = parsed.get("users", [])
assert users, "users section should be present"
# Find algo user
algo_user = None
for user in users:
if isinstance(user, dict) and user.get("name") == "algo":
algo_user = user
break
assert algo_user, "algo user should be defined"
# Check required user properties
required_props = ["sudo", "groups", "shell", "ssh_authorized_keys"]
missing = [prop for prop in required_props if prop not in algo_user]
assert not missing, f"algo user missing properties: {missing}"
# Verify sudo configuration
sudo_config = algo_user.get("sudo", "")
assert "NOPASSWD:ALL" in sudo_config, f"sudo config should allow passwordless access: {sudo_config}"
print("✅ User creation correct")
def test_runcmd_section(self):
"""Test that runcmd section will restart SSH correctly."""
print("🧪 Testing runcmd section...")
parsed = self.test_yaml_validity()
runcmd = parsed.get("runcmd", [])
assert runcmd, "runcmd section should be present"
# Check for SSH restart command
ssh_restart_found = False
for cmd in runcmd:
if "systemctl restart sshd" in str(cmd):
ssh_restart_found = True
break
assert ssh_restart_found, f"SSH restart command not found in runcmd: {runcmd}"
print("✅ runcmd section correct")
def test_indentation_consistency(self):
"""Test that sshd_config content has consistent indentation."""
print("🧪 Testing indentation consistency...")
cloud_init_content = create_expected_cloud_init()
# Extract the sshd_config content lines
lines = cloud_init_content.split("\n")
in_sshd_content = False
sshd_lines = []
for line in lines:
if "content: |" in line:
in_sshd_content = True
continue
elif in_sshd_content:
if line.strip() == "" and len(sshd_lines) > 0:
break
if line.startswith("runcmd:"):
break
sshd_lines.append(line)
assert sshd_lines, "Should be able to extract sshd_config content"
# Check that all non-empty lines have consistent 6-space indentation
non_empty_lines = [line for line in sshd_lines if line.strip()]
assert non_empty_lines, "sshd_config should have content"
for line in non_empty_lines:
# Each line should start with exactly 6 spaces
assert line.startswith(" ") and not line.startswith(" "), (
f"Line should have exactly 6 spaces indentation: {repr(line)}"
)
print("✅ Indentation is consistent")
def run_tests():
"""Run all tests manually (for non-pytest usage)."""
print("🚀 Cloud-init template validation tests")
print("=" * 50)
test_instance = TestCloudInitTemplate()
try:
test_instance.test_yaml_validity()
test_instance.test_required_sections()
test_instance.test_ssh_configuration()
test_instance.test_user_creation()
test_instance.test_runcmd_section()
test_instance.test_indentation_consistency()
print("=" * 50)
print("🎉 ALL TESTS PASSED!")
print("✅ Cloud-init template is working correctly")
print("✅ DigitalOcean deployment should succeed")
return True
except AssertionError as e:
print(f"❌ Test failed: {e}")
return False
except Exception as e:
print(f"❌ Unexpected error: {e}")
return False
if __name__ == "__main__":
success = run_tests()
sys.exit(0 if success else 1)