The ts_omit_<name> build tags omit a feature at build time; there has
been no way to do the same at runtime. Some users (either proactively
or in response to a security announcement) might like a way to disable
a feature that's linked-in in their binaries that they're not using.
Then a mitigation announcement can say "set this env var" without
asking users to rebuild or wait for a new release.
This adds env var TS_DISABLE_FEATURE, a comma-separated list of
feature names to disable, and the listed set is reported by the
debug-optional-features LocalAPI endpoint next to the registered set.
The legacy per-feature knobs such as TS_DISABLE_SSH_SERVER and
TS_DISABLE_TAILDROP keep working independently.
A disabled feature behaves as if it had not been linked: it is absent
from feature.IsRegistered, its hooks are unset, and its extensions and
handlers are not registered. Three pieces make that happen:
* feature.Register now returns bool, false when disabled, and
feature packages gate their registration init on it. It was added
to the feature packages that never called it (including taildrop
and ssh), which also completes the picture reported by
debug-optional-features. taildrop, routecheck, favorites, and
serviceclientprefs had registration split across several inits and
now register from one gated init.
* ipnext.RegisterExtension ignores a disabled feature's extension.
* feature.Hook.Set and feature.Hooks.Add walk the call stack and
silently skip when the calling package under feature/<name> is
disabled. This covers sub-packages such as
feature/captiveportal/netcheckhook, which cannot call Register
themselves without colliding with their parent, and future
packages whose authors forget the gate.
ssh/tailssh's registrations moved from its inits into tailssh.Register,
called from feature/ssh's gated init. The aws and kube state stores and
syspolicy's Windows store registration are gated too.
feature/register_disable_test.go runs this test binary as a child
process (it links condregister, as tailscaled does) with
TS_DISABLE_FEATURE set to every registered feature at once, and fails
if any of them register anyway, so a feature that ignores the variable
cannot land.
Updates #12614
Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>
Change-Id: I720af6ccab844ae060a9dfd1539fee577fd483e3
The BIRD (BGP) integration previously lived half in cmd/tailscaled
(which created a chirp client via a build-tag-gated file on some
platforms) and half in wgengine (which carried the client in its
Config and toggled the "tailscale" protocol as the node gained or
lost primary subnet router duty).
Move it all to a new feature/bird package, installed on the engine
via the new wgengine.HookNewBird hook, like other feature/* packages.
wgengine.Config.BIRDClient (and the wgengine.BIRDClient interface)
are replaced by a BIRDSocket path from which the engine constructs
the feature's Bird handle at startup. The subnet router overlap
detection and protocol toggling move into feature/bird, preserving
the previous ordering: state is recomputed before Reconfig's
ErrNoChanges early return and applied after the router is configured.
tailscaled keeps BIRD support by default on the platforms that
previously had it (linux, darwin, freebsd, openbsd) via
feature/condregister.
Also, add an integration test, as this feature lacked much test
coverage previously.
Updates #12614
Change-Id: I7866a50779e454c87933b358735f7dcd9e2b126f
Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>
Brad Fitzpatrick