Only allow traffic via the proxy in global-proxy test

pr-checks/checks/global-proxy.yml

@@ -5,6 +5,7 @@ versions:
   - nightly-latest
 container:
   image: ubuntu:22.04
+  options: --cap-add=NET_ADMIN
 services:
   squid-proxy:
     image: ubuntu/squid:latest
@@ -14,6 +15,24 @@ env:
   https_proxy: http://squid-proxy:3128
   CODEQL_ACTION_TOLERATE_MISSING_GIT_VERSION: true
 steps:
+  - name: Block direct internet access to force proxy usage
+    run: |
+      apt-get update -qq && apt-get install -y -qq iptables >/dev/null 2>&1
+      PROXY_IP=$(getent hosts squid-proxy | awk '{ print $1 }')
+      echo "Squid proxy IP: $PROXY_IP"
+      # Allow all traffic to the proxy container
+      iptables -A OUTPUT -d "$PROXY_IP" -j ACCEPT
+      # Allow DNS resolution
+      iptables -A OUTPUT -p udp --dport 53 -j ACCEPT
+      iptables -A OUTPUT -p tcp --dport 53 -j ACCEPT
+      # Allow loopback
+      iptables -A OUTPUT -o lo -j ACCEPT
+      # Allow already-established connections (from checkout/prepare-test)
+      iptables -A OUTPUT -m conntrack --ctstate ESTABLISHED,RELATED -j ACCEPT
+      # Block all other outbound HTTP and HTTPS, ensuring direct access fails
+      iptables -A OUTPUT -p tcp --dport 80 -j REJECT --reject-with tcp-reset
+      iptables -A OUTPUT -p tcp --dport 443 -j REJECT --reject-with tcp-reset
+      echo "Direct HTTP/HTTPS access is now blocked - all traffic must go through the proxy"
   - uses: ./../action/init
     with:
       languages: javascript