From bce5cb2ce5fe64f82a9ce3d2b5a6900bfdf9096f Mon Sep 17 00:00:00 2001
From: Markus Rudy <mr@edgeless.systems>
Date: Fri, 19 Jul 2024 14:34:09 +0200
Subject: [PATCH] genpolicy: harden CreateSandboxRequest checks

Hooks are executed on the host, so we don't expect to run hooks and thus
require that no hook paths are set.

Additional Kernel modules expand the attack surface, so require that
none are set. If a use case arises, modules should be allowlisted via
settings.

Signed-off-by: Markus Rudy <mr@edgeless.systems>
---
 src/tools/genpolicy/rules.rego                |  5 +++-
 .../testdata/createsandbox/testcases.json     | 23 +++++++++++++++++++
 2 files changed, 27 insertions(+), 1 deletion(-)

diff --git a/src/tools/genpolicy/rules.rego b/src/tools/genpolicy/rules.rego
index 3db3ed3dc7..a781b4e06e 100644
--- a/src/tools/genpolicy/rules.rego
+++ b/src/tools/genpolicy/rules.rego
@@ -15,7 +15,7 @@ default AddSwapRequest := false
 default CloseStdinRequest := false
 default CopyFileRequest := false
 default CreateContainerRequest := false
-default CreateSandboxRequest := true
+default CreateSandboxRequest := false
 default DestroySandboxRequest := true
 default ExecProcessRequest := false
 default GetOOMEventRequest := true
@@ -1117,6 +1117,9 @@ CreateSandboxRequest {
     print("CreateSandboxRequest: input.guest_hook_path =", input.guest_hook_path)
     count(input.guest_hook_path) == 0
 
+    print("CreateSandboxRequest: input.kernel_modules =", input.kernel_modules)
+    count(input.kernel_modules) == 0
+
     i_pidns := input.sandbox_pidns
     print("CreateSandboxRequest: i_pidns =", i_pidns)
     i_pidns == false
diff --git a/src/tools/genpolicy/tests/testdata/createsandbox/testcases.json b/src/tools/genpolicy/tests/testdata/createsandbox/testcases.json
index 4a024221b1..430c1d7af3 100644
--- a/src/tools/genpolicy/tests/testdata/createsandbox/testcases.json
+++ b/src/tools/genpolicy/tests/testdata/createsandbox/testcases.json
@@ -5,5 +5,28 @@
     "request": {
       "sandbox_pidns": false
     }
+  },
+  {
+    "description": "pidns",
+    "allowed": false,
+    "request": {
+      "sandbox_pidns": true
+    }
+  },
+  {
+    "description": "kernel modules",
+    "allowed": false,
+    "request": {
+      "sandbox_pidns": false,
+      "kernel_modules": [{"name": "evil.ko"}]
+    }
+  },
+  {
+    "description": "guest hooks",
+    "allowed": false,
+    "request": {
+      "sandbox_pidns": false,
+      "guest_hook_path": "/attacker/controlled/path"
+    }
   }
 ]