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
Add a new modular syslog feature providing a tailscaled --syslog flag
that sends the daemon's logs to the system syslog daemon instead of
stderr, which is useful when running as a daemon without a service
manager that captures stderr (e.g. OpenWrt's procd).
The feature package registers two new hooks: one to register its flag
before flag parsing, and one that tailscaled calls early in main to
redirect the standard library's default logger. Because logpolicy later
points the default logger at logtail, whose local console copy writes
to stderr, logpolicy now also consults the hook and sends its console
copy to the same sink (with timestamps disabled, as syslog records its
own).
The feature is linked by default only on Linux, FreeBSD, and OpenBSD,
and can be removed with the ts_omit_syslog build tag. If connecting to
the syslog daemon fails at startup, tailscaled logs a warning and
continues logging to stderr.
Fixes#16270
Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>
Change-Id: I8f3a92d4c1e6b70a5d29e4f61b3c874250a9de13
Brad Fitzpatrick