anet's only reason to need -ldflags=-checklinkname=0 is a pair of
//go:linkname pulls that refresh the IPv6 zone caches inside net and
x/net after it enumerates interfaces. localAddrs never resolves a zone
and drops link-local addresses anyway, so nebula was paying for that
flag, and disabling the linker's check for the whole binary, for
nothing it used.
Replace the dependency with the part of anet that matters: an
RTM_GETADDR dump on a netlink socket that is never bound, and
SIOCGIFNAME to name each index. Both are permitted to Android apps,
and it is the same path Bionic's getifaddrs takes for app UIDs. It is
built only for android; every other platform, Linux included, keeps
net.Interfaces.
One dump yields every interface with its addresses, so reshape the
seam to a single enumerator returning localInterface values with a
deferred Addrs. Android hands back what it already has; every other
platform still only asks for the addresses of interfaces the allow
list accepts.
Take the bind-free path unconditionally on android. The sepolicy is
keyed to the app's target SDK rather than the OS release, detecting
either needs cgo, and the path is valid on every release.
Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01B15ivF2aJUtLFdqJ4iz6zs
On Android 11+ the app sandbox denies bind() on netlink_route_socket, so
the stdlib's net.Interfaces fails with EACCES. localAddrs discarded that
error and returned an empty slice, so the node advertised no underlay
addresses and peers could only ever reach it at the address a lighthouse
observed. A device on the same LAN as a peer was unreachable at its LAN
address.
Split interface enumeration behind a build-tagged seam and use
github.com/wlynxg/anet on Android, which reads RTM_GETADDR from an
unbound socket. Interface addresses have to come from anet as well, since
net.Interface.Addrs goes back through the same denied path. Every other
platform keeps the net package implementation.
Stop discarding the enumeration errors, which are exceptional now that
the sandbox case is handled.
anet needs -ldflags=-checklinkname=0 on Go 1.23+. Nebula ships no Android
binaries, so build-test-mobile is unaffected, but consumers linking
Android artifacts will need the flag.
