Refresh agent signing keys from repository (Refs #64)

agent/install.sh

@@ -96,11 +96,6 @@ def trusted_json(path):
 
 trusted_directories(root)
 trusted_directories(config.parent)
-keyring = config.with_name('release-signing.gpg')
-try:
-    trusted_file(keyring)
-except FileNotFoundError:
-    raise SystemExit('Provision the publisher public key at /etc/electric-cherry/release-signing.gpg through a trusted channel before installing. Never obtain the trust key from the controller.') from None
 mountinfo = pathlib.Path('/proc/1/mountinfo')
 if mountinfo.exists():
     for line in mountinfo.read_text().splitlines():
@@ -147,7 +142,7 @@ PY
 if [ -f /etc/electric-cherry/agent.json ]; then existing_enrollment=true; fi
 if [ -d "$data_dir" ]; then existing_data_root=true; fi
 installation_preflight
-temporary_dir=$(mktemp -d)
+temporary_dir=$(mktemp -d /tmp/electric-cherry-install.XXXXXXXXXX)
 updater_timer_was_active=false
 update_lock_held=false
 activity_lock_held=false
@@ -172,23 +167,39 @@ installation_cleanup() {
     exit "$ec_install_status"
 }
 trap installation_cleanup EXIT
+# INSTALLATION_TRUST: always fetch directly from the repository, never the controller.
+key_status=$(curl --proto '=https' --tlsv1.2 --fail --silent --show-error \
+    --connect-timeout 25 --max-time 120 --max-filesize 262144 \
+    --header 'Cache-Control: no-cache' --write-out '%{http_code}' \
+    'https://gitea.thewrightserver.net/josh/electric-cherry/raw/branch/main/agent/release-signing.gpg' \
+    -o "$temporary_dir/release-signing.gpg")
+[ "$key_status" = 200 ] && [ -s "$temporary_dir/release-signing.gpg" ] || {
+    echo 'The release-signing repository did not return a public key. Installation stopped.' >&2
+    exit 1
+}
+# INSTALLATION_TRUST_END
 controller="${controller%/}"
 curl --proto '=https' --tlsv1.2 --fail --silent --show-error "$controller/api/agent/release/manifest.json" -o "$temporary_dir/manifest.json"
 curl --proto '=https' --tlsv1.2 --fail --silent --show-error "$controller/api/agent/release/manifest.json.sig" -o "$temporary_dir/manifest.json.sig"
 curl --proto '=https' --tlsv1.2 --fail --silent --show-error "$controller/api/agent/release/ec-agent.py" -o "$temporary_dir/ec-agent.py"
 curl --proto '=https' --tlsv1.2 --fail --silent --show-error "$controller/api/agent/release/ec-agent-update.py" -o "$temporary_dir/ec-agent-update.py"
-python3 - "$temporary_dir/manifest.json" "$temporary_dir/ec-agent.py" "$temporary_dir/ec-agent-update.py" /etc/electric-cherry/release-signing.gpg <<'PY'
+python3 - "$temporary_dir/manifest.json" "$temporary_dir/ec-agent.py" "$temporary_dir/ec-agent-update.py" "$temporary_dir/release-signing.gpg" <<'PY'
 # INSTALLATION_RELEASE: check both downloads before installing or executing either.
 import ast, hashlib, json, pathlib, re, stat, subprocess, sys, tempfile
 manifest_path = pathlib.Path(sys.argv[1])
 manifest_bytes = manifest_path.read_bytes()
 signature = manifest_path.with_name('manifest.json.sig')
 keyring = pathlib.Path(sys.argv[4])
-for path in (*reversed(keyring.parents), keyring):
+# The key lives in our private root-owned mktemp directory under sticky /tmp.
+# /tmp itself is intentionally writable; require protection of the directory
+# and file we created, rather than accepting a pre-existing host keyring.
+for path in (keyring.parent, keyring):
     info = path.lstat()
     expected_type = stat.S_ISREG if path == keyring else stat.S_ISDIR
     if not expected_type(info.st_mode) or info.st_uid != 0 or info.st_mode & 0o022:
         raise SystemExit('Release signing key must be a regular root-owned file in protected directories.')
+if not 0 < keyring.stat().st_size <= 256 * 1024:
+    raise SystemExit('Repository public key is empty or exceeds its size limit.')
 if len(manifest_bytes) > 16 * 1024 or signature.stat().st_size > 16 * 1024:
     raise SystemExit('Release signing metadata exceeds its size limit.')
 try: