no-mistakes(review): harden dsh token capture: loopback bind, atomic nginx config

scripts/capture-dsh-token.sh

@@ -10,6 +10,7 @@
 # 6. Reloads nginx
 
 set -euo pipefail
+umask 077
 
 # Kill any existing dsh-web instance first
 systemctl stop dsh-web 2>/dev/null || true
@@ -39,18 +40,36 @@ fi
 # Extract the token value (everything after "?token=")
 TOKEN_VALUE=$(echo "$TOKEN" | grep -oP "(?<=token=)[^ ]+")
 
-# Write the token to a file
+# Reject tokens that could break nginx config or the request URI
+if ! printf '%s' "$TOKEN_VALUE" | grep -qE '^[A-Za-z0-9._~+/=%:@-]+$'; then
+  echo "ERROR: token contains unsupported characters" >&2
+  exit 1
+fi
+
+# Write the token to a restricted file
 mkdir -p /etc/dsh-web
-echo "$TOKEN_VALUE" > /etc/dsh-web/launch-token
-echo "Captured token: $TOKEN_VALUE"
+printf '%s\n' "$TOKEN_VALUE" > /etc/dsh-web/launch-token
+chmod 600 /etc/dsh-web/launch-token
+echo "Captured dsh-web launch token"
 
 # Create the nginx config with the token (using printf to control expansion)
+NGINX_ENABLED="/etc/nginx/sites-enabled/dsh.token"
+NGINX_STAGE_DIR="/etc/nginx/sites-available"
+mkdir -p "$NGINX_STAGE_DIR"
+
+TMP_CONFIG="$(mktemp "$NGINX_STAGE_DIR/dsh.token.XXXXXX")"
+BACKUP=""
+if [ -f "$NGINX_ENABLED" ]; then
+  BACKUP="$(mktemp "$NGINX_STAGE_DIR/dsh.token.bak.XXXXXX")"
+  cp -p "$NGINX_ENABLED" "$BACKUP"
+fi
+
 {
   printf "server {\n"
-  printf "    listen 8081;\n"
+  printf "    listen 127.0.0.1:8081;\n"
   printf "    server_name _;\n"
   printf "    \n"
-  printf "    location /dsh-web-login {\n"
+  printf "    location = /dsh-web-login {\n"
   printf "        proxy_pass http://127.0.0.1:3080/?token=%s;\n" "$TOKEN_VALUE"
   printf "        proxy_http_version 1.1;\n"
   printf "        proxy_set_header Host 127.0.0.1:3080;\n"
@@ -66,12 +85,28 @@ echo "Captured token: $TOKEN_VALUE"
   printf "        proxy_set_header X-Forwarded-For \$proxy_add_x_forwarded_for;\n"
   printf "    }\n"
   printf "}\n"
-} > /etc/nginx/sites-enabled/dsh.token
+} > "$TMP_CONFIG"
+chmod 600 "$TMP_CONFIG"
 
-# Reload nginx
-nginx -t && /usr/sbin/nginx -s reload || {
-  echo "ERROR: failed to reload nginx" >&2
-  exit 1
+mv "$TMP_CONFIG" "$NGINX_ENABLED"
+CONFIG_APPLIED=1
+restore_on_exit() {
+  if [ "$CONFIG_APPLIED" -eq 1 ]; then
+    if [ -n "$BACKUP" ]; then
+      if cp -p "$BACKUP" "$NGINX_ENABLED" 2>/dev/null; then rm -f "$BACKUP"; fi
+    else
+      rm -f "$NGINX_ENABLED"
+    fi
+  fi
 }
+trap restore_on_exit EXIT
 
-echo "Token captured and nginx reloaded"
+if nginx -t; then
+  /usr/sbin/nginx -s reload
+  CONFIG_APPLIED=0
+  if [ -n "$BACKUP" ]; then rm -f "$BACKUP"; fi
+  echo "Token captured and nginx reloaded"
+else
+  echo "ERROR: nginx config test failed; rolling back" >&2
+  exit 1
+fi