Merge pull request 'chore(deps): update golang:1.26.4-alpine docker digest to 3ad5730' (#38) from renovate/golang-1.26.4-alpine into main

Reviewed-on: #27

.woodpecker/release-tag.yaml

@@ -44,7 +44,7 @@ steps:
       - bao kv get -mount secret -field RENOVATE_TOKEN renovate > /woodpecker/git_token
 
   - name: Auto-tag mt.1 on Tailscale bump
-    image: alpine/git:v2.52.0
+    image: alpine/git:v2.54.0
     environment:
       CI_REPO_URL: https://gitea.lumpiasty.xyz/lumpiasty/mikrotik-tailscale.git
     commands:

.woodpecker/renovate.yaml

@@ -46,7 +46,7 @@ steps:
       - bao kv get -mount secret -field GITHUB_COM_TOKEN renovate > /woodpecker/github_com_token
   - name: renovate
     # Renovate's built-in "woodpecker" manager tracks this image automatically.
-    image: renovate/renovate:43.220.0
+    image: renovate/renovate:43.227.0
     environment:
       # --- platform / target ---
       RENOVATE_PLATFORM: gitea

Dockerfile

@@ -32,7 +32,7 @@ FROM --platform=$BUILDPLATFORM tonistiigi/xx:1.9.0@sha256:c64defb9ed5a91eacb37f9
 # =============================================================================
 # Stage 1: Build Tailscale combined binary (cross-compiled, runs natively)
 # =============================================================================
-FROM --platform=$BUILDPLATFORM golang:1.26.4-alpine@sha256:f1ddd9fe14fffc091dd98cb4bfa999f32c5fc77d2f2305ea9f0e2595c5437c14 AS builder
+FROM --platform=$BUILDPLATFORM golang:1.26.4-alpine@sha256:3ad57304ad93bbec8548a0437ad9e06a455660655d9af011d58b993f6f615648 AS builder
 
 # renovate: datasource=github-releases depName=tailscale packageName=tailscale/tailscale versioning=semver
 ARG TAILSCALE_VERSION=v1.98.5
@@ -133,6 +133,31 @@ COPY patches/stderr_verbosity_filter.go cmd/tailscaled/
 #   gro                 — Generic Receive Offload (perf). Depends on netstack;
 #                         pulled in with it. Small, and improves throughput on
 #                         the netstack DNS/inject path.
+#   peerapiserver       — REQUIRED to be a functional exit node. In v1.98.5
+#                         'advertiseexitnode' DECLARES a dependency on
+#                         peerapiserver (featuretags.go Deps, "to run the ExitDNS
+#                         server"), but this build's allowlist works by stripping
+#                         individual ts_omit_ tags and does NOT re-resolve Deps —
+#                         so featuretags --min still emitted ts_omit_peerapiserver
+#                         and our advertiseexitnode opt-in alone left it omitted.
+#                         peerapiserver gates the entire PeerAPI HTTP server,
+#                         including the /dns-query DoH endpoint (peerapi.go,
+#                         guarded by buildfeatures.HasPeerAPIServer). Without it
+#                         initPeerAPIListenerLocked() returns early: the node
+#                         never advertises the PeerAPIDNS service, so exit-node
+#                         CLIENTS' exitNodeCanProxyDNS(thisNode) returns false.
+#                         With no tailnet global nameserver configured, the
+#                         client's resolver then has an empty Routes["."] and
+#                         returns an INSTANT authoritative SERVFAIL locally
+#                         (forwarder.go servfailResponse, aa=1, 0 ms, no I/O) —
+#                         i.e. devices using this router as their exit node could
+#                         not resolve PUBLIC names. Including peerapiserver makes
+#                         the node serve the exit-node DoH DNS proxy, so clients
+#                         get public DNS automatically (the normal exit-node
+#                         behavior) with no tailnet DNS config required.
+#                         peerapiserver has NO Deps and pulls in no large
+#                         subsystems — a small addition. (outboundproxy is NOT
+#                         needed for this and stays omitted.)
 #
 # Everything else remains omitted, including (rationale):
 #   clientupdate  — DELIBERATELY removed. The built-in updater would download
@@ -180,6 +205,7 @@ RUN mkdir -p /out && \
           -e 's/ts_omit_ipnbus,\{0,1\}//g' \
           -e 's/ts_omit_netstack,\{0,1\}//g' \
           -e 's/ts_omit_gro,\{0,1\}//g' \
+          -e 's/ts_omit_peerapiserver,\{0,1\}//g' \
           -e 's/,$//' \
     ) && \
     echo "Build tags: ${TAGS}" && \
@@ -277,7 +303,7 @@ RUN printf '%s\n' \
 # only for this one lightweight probe step (busybox --help per applet), not
 # for the compile itself. The probe can alternatively be skipped by using
 # a pre-enumerated applet list, but the current approach is simpler.
-FROM --platform=$BUILDPLATFORM alpine:3.24.0@sha256:a2d49ea686c2adfe3c992e47dc3b5e7fa6e6b5055609400dc2acaeb241c829f4 AS busybox
+FROM --platform=$BUILDPLATFORM alpine:3.24.1@sha256:28bd5fe8b56d1bd048e5babf5b10710ebe0bae67db86916198a6eec434943f8b AS busybox
 
 # Copy xx cross-compilation helpers (xx-clang, xx-apk, xx-info, etc.)
 COPY --from=xx / /

docs/DESIGN.md

@@ -155,6 +155,7 @@ that's a separate build, not just a `--platform` change.
 | `accept-routes` | Receive subnet routes from other tailnet nodes |
 | DNS / MagicDNS | Resolve `*.ts.net` names (resolver + resolv.conf manager). **Note:** serving `100.100.100.100` also requires `netstack` — see [Why netstack is required (even with a kernel TUN)](#why-netstack-is-required-even-with-a-kernel-tun) |
 | `netstack` + `gro` | gVisor userspace stack. Counter-intuitively **required** to serve MagicDNS on `100.100.100.100`, even though the router uses a real kernel TUN — see [Why netstack is required (even with a kernel TUN)](#why-netstack-is-required-even-with-a-kernel-tun) |
+| `peerapiserver` | Serves the PeerAPI, including the `/dns-query` DoH endpoint that lets **exit-node clients resolve public DNS automatically**. A declared dependency of `advertise-exit-node` that the allowlist didn't pull in — see [Why peerapiserver is required for exit-node DNS](#why-peerapiserver-is-required-for-exit-node-dns) |
 | portmapper (NAT-PMP/PCP/UPnP) | Punch through upstream NAT |
 | listenrawdisco | Raw socket disco for better NAT traversal |
 | health | Powers `tailscale status` output |
@@ -308,6 +309,80 @@ itself is refactored — re-test whether `netstack` can be dropped again. The
 canary is simple: from inside the container, `dig google.com @100.100.100.100`
 must return answers and `ping <host>.<tailnet>.ts.net` must resolve.
 
+### Why peerapiserver is required for exit-node DNS
+
+This is a second non-obvious DNS inclusion, and it exposes a limitation of the
+allowlist build strategy.
+
+**Symptom.** With `netstack` enabled, MagicDNS worked from the router and from
+LAN hosts, including public names. But a device using this router **as its exit
+node** could not resolve public names: `dig google.com @100.100.100.100` on the
+*client* returned an instant authoritative `SERVFAIL` (`flags: qr aa rd ad`,
+`Query time: 0 msec`, "recursion not available"). Tailnet names and raw-IP
+connectivity (e.g. `ping 1.1.1.1`) through the exit node worked.
+
+**Root cause.** The `SERVFAIL` is generated **on the client**, locally, with no
+network I/O — which is why it is instant and authoritative. The path
+(traced through v1.98.5 source):
+
+1. The client's query for `google.com` reaches its in-process resolver, which
+   determines the name is not a tailnet name and marks it for forwarding
+   (`net/dns/resolver/tsdns.go`).
+2. The forwarder looks up which upstream resolver to use for the catch-all
+   `"."` route (`net/dns/resolver/forwarder.go` → `resolvers()`).
+3. That route set is **empty**, so `forwardWithDestChan` short-circuits and
+   synthesises an authoritative `SERVFAIL` (`servfailResponse`, `aa=1`) without
+   opening any socket. The query never reaches this router at all.
+
+Why the route set is empty: when a client selects an exit node,
+`dnsConfigForNetmap` (`ipn/ipnlocal/node_backend.go`) deliberately routes **all**
+default DNS through the exit node and drops the client's own LAN/system
+resolver — the whole premise of an exit node is "send everything, including
+DNS, through me." It does this by setting the client's default resolver to the
+exit node's **DoH proxy** URL (`http://<peer>/dns-query`). But that only happens
+if `exitNodeCanProxyDNS(thisRouter)` returns true — i.e. if **this router
+advertises a working PeerAPI DoH endpoint**. If it does not, and there is no
+tailnet global nameserver to fall back to, the client ends up with an empty
+default route and returns `SERVFAIL`.
+
+**Why this router didn't advertise the DoH proxy.** The `/dns-query` DoH
+endpoint is part of the **PeerAPI server**, gated by
+`buildfeatures.HasPeerAPIServer` (`ipn/ipnlocal/peerapi.go`). With
+`ts_omit_peerapiserver`, `initPeerAPIListenerLocked()` returns early: no PeerAPI
+listener is created, the `PeerAPIDNS` service is never advertised, and
+`peerCanProxyDNS()` is false for this node on every client.
+
+**The allowlist gap that caused it.** In `feature/featuretags/featuretags.go`,
+`advertiseexitnode` **declares a dependency on `peerapiserver`** ("to run the
+ExitDNS server"). Upstream's own `--add` resolution would have pulled it in.
+But this build's allowlist works differently: it runs `featuretags --min` to get
+the full omit set, then strips the specific `ts_omit_<feature>` tags it wants —
+it does **not** re-resolve transitive `Deps`. So opting in `advertiseexitnode`
+did not pull in `peerapiserver`, and `featuretags --min` had emitted
+`ts_omit_peerapiserver`, leaving the node an exit node *without* its declared
+ExitDNS dependency — a feature combination upstream's graph says shouldn't
+occur. Including `peerapiserver` explicitly closes the gap.
+
+> **Known limitation:** the allowlist (strip-individual-`ts_omit_`-tags) does
+> not resolve feature dependencies. When opting a feature in, check its `Deps`
+> in `featuretags.go` and add them explicitly. `peerapiserver` is the only such
+> gap found and fixed so far; a full dependency audit has not been done.
+
+**Cost.** Negligible. `peerapiserver` has **no** `Deps` and pulls in no large
+subsystems; measured at ~+10 kB on the UPX'd binary (arm64), rootfs unchanged
+within measurement noise.
+
+**Result.** The router now serves the exit-node DoH DNS proxy, so devices using
+it as their exit node resolve public names automatically — the normal exit-node
+behavior — with **no** tailnet DNS configuration required. (Setting a tailnet
+global nameserver in the admin console is an alternative runtime fix that also
+works, by populating the client's default resolver directly; it is not required
+once the router serves the proxy.)
+
+**Canary for future bumps:** from a client using this router as exit node,
+`dig google.com @100.100.100.100` must return real answers with `flags: ... ra`
+(recursion available) and a non-zero query time.
+
 ### Log verbosity filtering
 
 Upstream `tailscaled` embeds verbosity tags (`[v1]`, `[v2]`, …) inside its log