Entrypoint checks DATA_DIR in full before acting on it as root (closes #80)

`bin/entrypoint.sh` now checks `DATA_DIR` before it creates anything or
changes an owner or mode: it must be `/data` or a path below it with no
`.`, `..` or empty part, and no part of it that exists, `/data`
included, may be a symbolic link. Anything else stops the start with one
message naming `DATA_DIR`. Only then does it create `DATA_DIR`, give
`/data` and everything in it to `netwatch` (`chown -R -h`, so a link in
it is not followed) and set mode 750 on `/data` and `DATA_DIR`. The
README section "Running under upaas" says which values are accepted.

Model: opus-5-5

.gitea/workflows/check.yml

@@ -6,5 +6,7 @@ jobs:
         steps:
             # actions/checkout v4.2.2, 2026-02-22
             - uses: actions/checkout@11bd71901bbe5b1630ceea73d27597364c9af683
-            # script/cibuild builds the image, whose stages run every check.
-            - run: script/cibuild
+            # script/cibuild bootstraps, runs every check and builds the
+            # image. script/bootstrap links what it installs into
+            # ~/.local/bin, so that has to be on PATH for the rest.
+            - run: PATH="$HOME/.local/bin:$PATH" script/cibuild

Dockerfile

@@ -77,8 +77,9 @@ COPY --from=frontend /app/dist /usr/share/nginx/html
 COPY --from=builder /src/netwatch-server /usr/local/bin/netwatch-server
 COPY bin/entrypoint.sh /usr/local/bin/entrypoint.sh
 
+# bin/entrypoint.sh creates DATA_DIR at start and gives it and /data to
+# the netwatch user, whatever is mounted there.
 ENV DATA_DIR=/data/reports
-RUN mkdir -p /data/reports && chown -R netwatch:netwatch /data
 VOLUME /data
 
 # The default public port; PORT changes it.

README.md

@@ -36,12 +36,12 @@ The Go backend in `backend/` has its own `script/` directory and shim Makefile
 (see [backend/README.md](backend/README.md)). The root scripts cover both
 halves, so the root `make check` fails if either one is broken. We provide:
 
-- `script/bootstrap` — install all dependencies (pinned node via nvm if needed,
-  yarn via corepack, `yarn install --frozen-lockfile`, the pinned Go unless one
-  at least as new as `backend/go.mod` asks for is installed, and the Go
-  modules), linking what it installs itself into `~/.local/bin`, which has to be
-  on `PATH`. It installs no Go linter and not Docker: `make lint` runs the
-  linter in Docker
+- `script/bootstrap` — install all dependencies (the pinned node via nvm unless
+  one new enough for the frontend's dependencies is installed, yarn via
+  corepack, `yarn install --frozen-lockfile`, the pinned Go unless one at least
+  as new as `backend/go.mod` asks for is installed, and the Go modules), linking
+  what it installs itself into `~/.local/bin`, which has to be on `PATH`. It
+  installs no Go linter and not Docker: `make lint` runs the linter in Docker
 - `script/setup` — make a fresh clone ready for development: bootstrap plus the
   git pre-commit hook
 - `script/projectname` — print the project name (used for the Docker image tag)
@@ -192,8 +192,9 @@ only inside the container, on `127.0.0.1:8081`. The image:
 - Sends the security headers `REPO_POLICIES.md` requires on every response, as
   `security-headers.conf` sets them, in place of the backend's own
 - Stores reports in `DATA_DIR`, `/data/reports` by default, on the `/data`
-  volume. The backend runs as user `netwatch` (uid 1000), so a directory
-  bind-mounted at `/data` must be writable by uid 1000
+  volume. Before the backend starts, the image creates `DATA_DIR` and gives it
+  and `/data` to user `netwatch` (uid 1000), which the backend runs as, so a
+  host directory bind-mounted at `/data` ends up owned by uid 1000
 - Writes buffered reports to disk on `docker stop`, and exits non-zero if nginx
   or the backend exits on its own, so the platform restarts it
 
@@ -203,16 +204,6 @@ What the [upaas](https://git.eeqj.de/sneak/upaas) app for netwatch needs:
 
 - **Port:** container port `8080`.
 - **Volume:** container path `/data`; the reports are kept in `/data/reports`.
-- **First run:** upaas bind-mounts the host directory it is given and does not
-  create it, and the backend, which runs as uid 1000, does not start unless it
-  can write there. Create the directory, owned by uid 1000, before the first
-  deploy:
-
-    ```bash
-    mkdir -p /path/to/data
-    chown 1000:1000 /path/to/data
-    ```
-
 - **Environment variables:** none is required. An empty one counts as unset, and
   one set to a value netwatch cannot use stops the container at start, with the
   reason in its log.
@@ -225,8 +216,10 @@ What the [upaas](https://git.eeqj.de/sneak/upaas) app for netwatch needs:
     - `CORS_ALLOWED_ORIGINS`, default empty: other origins whose pages may call
       the API
     - `DEBUG`, default `false`: debug logging
-    - `DATA_DIR`, default `/data/reports`: leave unset; reports kept outside
-      `/data` do not survive a redeploy
+    - `DATA_DIR`, default `/data/reports`: the directory the reports are kept
+      in: `/data` or a path below it, with no `.` or `..` part and no extra `/`.
+      The container also stops if a part of the path that exists, `/data`
+      included, is a symbolic link
     - `TRUSTED_PROXIES`, default empty: set it to the address the reverse proxy
       in front of the container connects from, as an IP address or CIDR; several
       are separated by commas. nginx takes the client address from

TODO.md

@@ -23,12 +23,38 @@ latest run passes.
 
 # Completed Steps
 
+- 2026-09-29: `bin/entrypoint.sh` checks `DATA_DIR` in full before it acts on it
+  as root (issue #80): `DATA_DIR` must be `/data` or a path below it with no
+  `.`, `..` or empty part, and no part of it that exists, `/data` included, may
+  be a symbolic link; anything else stops the start with a message naming
+  `DATA_DIR`. Only then is `DATA_DIR` created and `/data` given to `netwatch`,
+  so a refused start no longer creates directories outside `/data`, and
+  `DATA_DIR=/etc` no longer gives `/etc` to `netwatch`. The `README.md` section
+  "Running under upaas" says which values are accepted
+- 2026-09-29: the container sets up its own data directory (issue #75):
+  `bin/entrypoint.sh`, still as root, creates `DATA_DIR` if missing and gives it
+  and `/data` to the `netwatch` user with mode 750 before starting the backend
+  as that user, so an empty host directory owned by root, or one holding files
+  from another uid, works with no step on the host. It stops the start instead
+  when a symbolic link is on the path to `DATA_DIR`, since root would change
+  whatever the link points to. The `README.md` first-run step that created and
+  chowned the host directory is gone, and the image no longer sets that
+  ownership at build time
 - 2026-09-29: CI can no longer pass on checks that did not run (issue #37):
   `script/cibuild` is now the org model, byte for byte. It runs
   `script/bootstrap` and `script/check`, then builds the image with `--no-cache`
   and the version from `git describe` as the `VERSION` build argument, where it
   used to be a plain `docker build .` whose check steps could come from the
-  build cache
+  build cache. The workflow puts `~/.local/bin`, where bootstrap links what it
+  installs, on the step's `PATH`, and bootstrap now installs its pinned node
+  when the installed one is older than the frontend's dependencies need
+- 2026-09-29: `backend/.golangci.yml` re-vendored from `sneak/prompts` (issue
+  #41): `gomodguard`, deprecated in golangci-lint v2.12.0, is disabled and its
+  successor `gomodguard_v2` enabled with the org block list, so lint runs print
+  no deprecation warning. The new file also turns `depguard` on with its
+  `test-support` rule, which keeps `net/http/httptest` out of non-test code;
+  netwatch adds no entries of its own to that rule. `backend/script/lint` checks
+  the new sha256
 - 2026-09-29: nginx sends the security headers `REPO_POLICIES.md` requires on
   every response (issue #18), including errors, `/assets/` and what it passes on
   from the backend, whose own copies it drops so each header goes out once. They
@@ -197,9 +223,3 @@ latest run passes.
   (main always green policy)
 - Decide what to do with untracked resume.sh: commit it, gitignore it, or delete
   it
-- Upstream fix needed in `sneak/prompts`: the org-standard `.golangci.yml`
-  enables `gomodguard`, which golangci-lint v2.12.2 reports as deprecated since
-  v2.12.0 and replaced by `gomodguard_v2`, so every backend lint run prints a
-  deprecation warning. The file is standardized and must never be edited in this
-  repo, so nothing can be done here beyond tracking it — tracked at
-  <https://git.eeqj.de/sneak/netwatch/issues/41>

backend/.golangci.yml

@@ -10,14 +10,20 @@ run:
 
 linters:
   default: all
+  enable:
+    # Successor to the deprecated gomodguard. Named explicitly, rather than
+    # left to `default: all`, because it carries the module policy below.
+    - gomodguard_v2
   disable:
     # Genuinely incompatible with project patterns
     - exhaustruct      # Requires all struct fields
-    - depguard         # Dependency allow/block lists
     - godot            # Requires comments to end with periods
-    - wsl              # Deprecated, replaced by wsl_v5
     - wrapcheck        # Too verbose for internal packages
     - varnamelen       # Short names like db, id are idiomatic Go
+    # Deprecated: the warning is attached to the old name, so it is
+    # silenced by disabling that name, not by enabling the successor.
+    - wsl              # Deprecated, replaced by wsl_v5
+    - gomodguard       # Deprecated, replaced by gomodguard_v2
   settings:
     lll:
       line-length: 88
@@ -28,6 +34,64 @@ linters:
       max-complexity: 15
     dupl:
       threshold: 100
+    depguard:
+      # Test-support code must not be compiled into the shipped binary. A
+      # test-support package exists to hand a test privileges the program
+      # itself must never have, so a file that is not a test must not import
+      # one. Test files, and the files inside a package whose directory name
+      # ends in `test`, are where that code belongs, and are exempt.
+      #
+      # The deny list below is the one part of this file a repository is
+      # expected to extend, and the only part it may. depguard matches an
+      # import path against a list of prefixes, so it cannot be told "any path
+      # whose last segment ends in test"; a repository's own test-support
+      # packages have to be named here one at a time, by full import path,
+      # under a module path that differs from repository to repository. Add
+      # them; change nothing else.
+      rules:
+        test-support:
+          list-mode: lax
+          files:
+            - "$all"
+            - "!$test"
+            - "!**/*test/**"
+          deny:
+            - pkg: net/http/httptest
+              desc: >-
+                Test-support code belongs in test files and in packages whose
+                directory name ends in test, not in the shipped binary.
+    # Only decisions already recorded in the Go package defaults are
+    # listed here. Every entry matches the module path exactly.
+    gomodguard_v2:
+      blocked:
+        - module: github.com/rs/zerolog
+          recommendations:
+            - log/slog
+          reason: "Structured logging is stdlib log/slog."
+        # One entry per pre-fork module path, because the later releases
+        # are separate paths. A prefix match would be shorter but would
+        # also reach github.com/go-redis/redismock, the test double for
+        # the successor these entries recommend.
+        - module: github.com/go-redis/redis
+          recommendations:
+            - github.com/redis/go-redis/v9
+          reason: "Pre-fork module; use the maintained go-redis v9."
+        - module: github.com/go-redis/redis/v7
+          recommendations:
+            - github.com/redis/go-redis/v9
+          reason: "Pre-fork module; use the maintained go-redis v9."
+        - module: github.com/go-redis/redis/v8
+          recommendations:
+            - github.com/redis/go-redis/v9
+          reason: "Pre-fork module; use the maintained go-redis v9."
+        - module: github.com/sergi/go-diff
+          recommendations:
+            - github.com/aymanbagabas/go-udiff
+          reason: "No unified diff output; use go-udiff."
+        - module: github.com/hexops/gotextdiff
+          recommendations:
+            - github.com/aymanbagabas/go-udiff
+          reason: "Unmaintained fork; use go-udiff."
 
 issues:
   max-issues-per-linter: 0

backend/README.md

@@ -104,7 +104,8 @@ this server. The image's entrypoint, `bin/entrypoint.sh`, starts the server as
 user `netwatch` (uid 1000) with `BIND_ADDRESS=127.0.0.1` and `PORT=8081`, so
 only nginx reaches it, and with `TRUSTED_PROXIES=127.0.0.1/32`, so it takes the
 client address nginx passes on and no other. `DATA_DIR` is `/data/reports`, on
-the `/data` volume, which `netwatch` owns. nginx replaces the security headers
+the `/data` volume; the entrypoint creates it and gives it and `/data` to
+`netwatch` before starting the server. nginx replaces the security headers
 this server sets with those in the root `security-headers.conf`, so those are
 what clients of the image see.
 

backend/script/lint

@@ -14,7 +14,7 @@ set -eu
 
 ROOT="$(cd "$(dirname "$0")/.." && pwd -P)"
 
-GOLANGCI_CONFIG_SHA256="021cc83f4e6fc7c31b95b34b846723dfcf20b66b7baeea1dc40406e643346bcb"
+GOLANGCI_CONFIG_SHA256="a79b63a254602a5318db5d0e9a06bc71b84bf0c1d896305229d8bfed1d1b1776"
 
 main() {
     cd "$ROOT"

bin/entrypoint.sh

@@ -61,6 +61,47 @@ for proxy in $(printf '%s' "$TRUSTED_PROXIES" | tr ',' ' '); do
     echo "set_real_ip_from $cidr;"
 done > /etc/nginx/trusted-proxies.conf
 
+# netwatch-server keeps its report files in DATA_DIR, on the /data
+# volume, which may be a host directory owned by root or by another
+# uid. /data and everything in it are given to the netwatch user here,
+# and /data and DATA_DIR get the mode the server gives a directory it
+# creates, so the host directory needs no preparing.
+#
+# This runs as root, so nothing is created or changed until DATA_DIR is
+# known to be /data or a path below it, with no '.', '..' or empty
+# part, and no part of it that exists, /data included, is a symbolic
+# link: the netwatch user can put one in /data, and root would follow
+# it anywhere in the container. Nothing else runs in the container yet,
+# so no link can appear after the check.
+export DATA_DIR="${DATA_DIR:-/data/reports}"
+data_dir_ok() {
+    # With a / added at the end, a last part of '.' or '..', and a / at
+    # the end, match these patterns too.
+    case "$DATA_DIR/" in
+        */./* | */../* | *//*) return 1 ;;
+        /data/*) ;;
+        *) return 1 ;;
+    esac
+    # Each part from DATA_DIR up to /data. [ -L ] is false for a part
+    # that does not exist.
+    dir="$DATA_DIR"
+    while [ "$dir" != /data ]; do
+        [ -L "$dir" ] && return 1
+        dir="${dir%/*}"
+    done
+    [ ! -L /data ]
+}
+if ! data_dir_ok; then
+    echo "entrypoint: DATA_DIR must be /data or a path below it, with no" \
+        "'.', '..', extra '/' or symbolic link on it, not '$DATA_DIR'" >&2
+    exit 1
+fi
+mkdir -p "$DATA_DIR" || exit 1
+# -h: a symbolic link in /data is itself given to netwatch, not what it
+# points to.
+chown -R -h netwatch:netwatch /data || exit 1
+chmod 750 /data "$DATA_DIR" || exit 1
+
 # A stop signal is only noted here; the loop below acts on it.
 stop_requested=""
 trap 'stop_requested=yes' TERM INT

script/bootstrap

@@ -3,12 +3,12 @@
 # this repo. Idempotent: every install is guarded by a check so already
 # installed tools are skipped. Base tooling comes from nix, apt, brew,
 # or apk (detected in that order); assumes nothing is present. Node is
-# used directly if installed; otherwise it is installed at a pinned
-# version via nvm (installing nvm itself first, from a hash-verified
-# release archive, never curl | sh). Go, with its gofmt, is used
-# directly if it is at least the version backend/go.mod asks for;
-# otherwise the pinned Go release is installed from its hash-verified
-# archive.
+# used directly if it is at least NODE_MIN_VERSION; otherwise it is
+# installed at a pinned version via nvm (installing nvm itself first,
+# from a hash-verified release archive, never curl | sh). Go, with its
+# gofmt, is used directly if it is at least the version backend/go.mod
+# asks for; otherwise the pinned Go release is installed from its
+# hash-verified archive.
 #
 # What this script installs outside the system package manager lives
 # under $HOME and is linked into ~/.local/bin, where make and the git
@@ -23,6 +23,10 @@ ROOT="$(cd "$(dirname "$0")/.." && pwd -P)"
 
 # Pinned versions, 2026-07-07
 NODE_VERSION="22.17.0"
+# The oldest node the frontend's dependencies accept: the "engines"
+# field of puppeteer-core 25.5.0, the most demanding of them, asks for
+# 22.12.0 or newer, 2026-09-29. An older installed node is not used.
+NODE_MIN_VERSION="22.12.0"
 NVM_VERSION="0.40.3"
 # sha256 of https://github.com/nvm-sh/nvm/archive/refs/tags/v0.40.3.tar.gz
 NVM_SHA256="5f4d6aaa04a177dc93c985e31dbc411ab6b8c6e1e21d8015dbc1372625fcd1d0"
@@ -136,8 +140,22 @@ ensure_nvm() {
     rm -rf "$tmp"
 }
 
+# node_ok: the node on PATH is at least NODE_MIN_VERSION. node itself
+# compares the two: major, then minor, then patch.
+node_ok() {
+    if missing node; then return 1; fi
+    node -e '
+        const have = process.versions.node.split(".").map(Number);
+        const want = process.argv[1].split(".").map(Number);
+        for (let i = 0; i < 3; i++) {
+            if (have[i] !== want[i]) process.exit(have[i] > want[i] ? 0 : 1);
+        }
+    ' "$NODE_MIN_VERSION"
+}
+
+# ensure_node: unless node_ok, install NODE_VERSION and link its node.
 ensure_node() {
-    if ! missing node; then return 0; fi
+    if node_ok; then return 0; fi
     ensure_nvm
     nvm_sh "nvm install $NODE_VERSION"
     link_bin "$HOME/.nvm/versions/node/v$NODE_VERSION/bin/node" node