From ae76e6c2bc1e135fd953373dc8ab1a5d5ca7dff6 Mon Sep 17 00:00:00 2001
From: Michael Martin <michael.martin@konghq.com>
Date: Tue, 23 Jan 2024 11:22:16 -0800
Subject: [PATCH] fix(wasm): do not call attach() on re-entrancy

---
 changelog/unreleased/kong/wasm-attach.yml |  5 +++++
 kong/runloop/wasm.lua                     | 25 ++++++++++++++---------
 2 files changed, 20 insertions(+), 10 deletions(-)
 create mode 100644 changelog/unreleased/kong/wasm-attach.yml

diff --git a/changelog/unreleased/kong/wasm-attach.yml b/changelog/unreleased/kong/wasm-attach.yml
new file mode 100644
index 000000000000..99ae358d4018
--- /dev/null
+++ b/changelog/unreleased/kong/wasm-attach.yml
@@ -0,0 +1,5 @@
+message: >
+  **proxy-wasm**: Fixed "previous plan already attached" error thrown when a
+  filter triggers re-entrancy of the access handler.
+type: bugfix
+scope: Core
diff --git a/kong/runloop/wasm.lua b/kong/runloop/wasm.lua
index 70f36b798adc..9bb697cdda1b 100644
--- a/kong/runloop/wasm.lua
+++ b/kong/runloop/wasm.lua
@@ -922,17 +922,22 @@ function _M.attach(ctx)
 
   ctx.ran_wasm = true
 
-  local ok, err = proxy_wasm.attach(chain.c_plan)
-  if not ok then
-    log(CRIT, "failed attaching ", chain.label, " filter chain to request: ", err)
-    return kong.response.error(500)
-  end
+  local ok, err
+  if not ctx.wasm_attached then
+    ctx.wasm_attached = true
 
-  ok, err = proxy_wasm.set_host_properties_handlers(properties.get,
-                                                    properties.set)
-  if not ok then
-    log(CRIT, "failed setting host property handlers: ", err)
-    return kong.response.error(500)
+    ok, err = proxy_wasm.attach(chain.c_plan)
+    if not ok then
+      log(CRIT, "failed attaching ", chain.label, " filter chain to request: ", err)
+      return kong.response.error(500)
+    end
+
+    ok, err = proxy_wasm.set_host_properties_handlers(properties.get,
+                                                      properties.set)
+    if not ok then
+      log(CRIT, "failed setting host property handlers: ", err)
+      return kong.response.error(500)
+    end
   end
 
   jit.off(proxy_wasm.start)