The post-stabilization reconcile verifies rule text, which cannot tell a
live redirect from an anchor pf has stopped evaluating. Sleep/wake QA
caught exactly that split: references intact, anchor rules intact,
post-load verification passed, and every query through the system
resolver timing out while the direct listener answered.
Nothing else probed. The interception probe monitor stands down while
stabilization owns pf and is never re-armed afterwards, so functional
recovery waited for the periodic watchdog - 11 seconds in the captured
run, up to a full 30-second interval - on a host whose link and default
route were already back. The watchdog's probe then failed once, forced a
reload, and public and VPN split-DNS both recovered immediately.
Probe once at the end of stabilization and, if it fails, force exactly
one reload and confirm with one more probe. Not the probe monitor: that
keeps probing for ~7.5s and can force a reload per failed probe, where
this path needs a single bounded repair before handing back to the
watchdog. Skipped when a monitor already owns probing, when intercept
state is gone, or during exec backoff.
Hand ownership over deterministically rather than skipping on sight. A
probe monitor started by an ignored network change claimed
functional-probe ownership before checking whether it could work, then
stood down because stabilization still owned pf; the verifier read that
claimed flag as "somebody is probing" and skipped, so neither path
probed and recovery fell back to the watchdog anyway. The monitor now
checks eligibility before claiming, and the verifier waits out a holder
that releases, yielding only to one that keeps probing.
Extract the completion block into finishPFStabilization so the wiring is
testable, and cover the bounded repair, the healthy path that must not
reload, a prober that claims and stands down, a prober that keeps
working, and a monitor that must not claim ownership while stabilizing.
IPv6 DNS interception on macOS is not feasible with current pf capabilities.
The kernel rejects sendmsg from [::1] to global unicast (EINVAL), nat on lo0
doesn't fire for route-to'd packets, raw sockets bypass routing but pf doesn't
match them against rdr state, and DIOCNATLOOK can't be used because bind()
fails for non-local addresses.
Replace all IPv6 interception code with a simple pf block rule:
block out quick on ! lo0 inet6 proto { udp, tcp } from any to any port 53
macOS automatically retries DNS over IPv4 when IPv6 is blocked.
Changes:
- Remove rawipv6_darwin.go and rawipv6_other.go
- Remove [::1] listener spawn on macOS (needLocalIPv6Listener returns false)
- Remove IPv6 rdr, route-to, pass, and reply-to pf rules
- Add block rule for all outbound IPv6 DNS
- Update docs/pf-dns-intercept.md with what was tried and why it failed
macOS rejects sendmsg from [::1] to global unicast IPv6 (EINVAL), and
nat on lo0 doesn't fire for route-to'd packets (pf skips translation
on the second interface pass). ULA addresses on lo0 also fail (EHOSTUNREACH
- kernel segregates lo0 routing).
Solution: wrap the [::1] UDP listener's ResponseWriter with rawIPv6Writer
that sends responses via SOCK_RAW (IPPROTO_UDP) on lo0, bypassing the
kernel's routing validation. pf's rdr state reverses the address
translation on the response path.
Changes:
- Add rawipv6_darwin.go: rawIPv6Writer wraps dns.ResponseWriter, sends
UDP responses via raw IPv6 socket with proper checksum calculation
- Add rawipv6_other.go: no-op wrapIPv6Handler for non-darwin platforms
- Remove nat rules from pf anchor (no longer needed)
- Block IPv6 TCP DNS (block return) - falls back to IPv4 (~1s, rare)
- Remove IPv6 TCP rdr/route-to/pass rules (only UDP intercepted)
Implement DNS interception on macOS using pf (packet filter):
- Anchor injection into running ruleset (not /etc/pf.conf)
- route-to lo0 + rdr rules for locally-originated DNS capture
- _ctrld group exemption so ctrld's own queries bypass interception
- Watchdog to detect and restore wiped anchor rules
- Probe-based auto-heal for Parallels VM pf corruption
- IPv6 DNS blocking and block-return for clean timeouts
- Interface-specific tunnel detection for VPN coexistence
- Port 5354 fallback in intercept mode
Includes pf technical reference docs and test scripts.
Squashed from intercept mode development on v1.0 branch (#497).
Anthony Wong