From c24f3f43a45e0f763bc3ff7a9264f343b2f35b73 Mon Sep 17 00:00:00 2001
From: "mergify[bot]" <37929162+mergify[bot]@users.noreply.github.com>
Date: Mon, 5 Dec 2022 18:16:28 +1030
Subject: [PATCH] packetbeat/protos/memcache: don't panic when a transaction is
 empty (#33853) (#33936)

When a *transaction is constructed from a UDP stream, but has no request
and no response, onTransaction is handed a nil *transaction, resulting in
a panic in Event when the *transaction.Notes field is accessed. The panic
is not recovered by ParseUDP's recover because the panic happens in a
separate goroutine. So be more careful with pointer dereferencing in this
path and put a separate recover in the time.AfterFunc-called closure.

(cherry picked from commit 248c9b0fccb261ec1772c7a38448edb2274aec64)

Co-authored-by: Dan Kortschak <90160302+efd6@users.noreply.github.com>
---
 CHANGELOG.next.asciidoc                  | 1 +
 packetbeat/protos/memcache/memcache.go   | 3 +++
 packetbeat/protos/memcache/plugin_udp.go | 4 ++++
 3 files changed, 8 insertions(+)

diff --git a/CHANGELOG.next.asciidoc b/CHANGELOG.next.asciidoc
index 2cd3f8b03b1d..e6061e32d1be 100644
--- a/CHANGELOG.next.asciidoc
+++ b/CHANGELOG.next.asciidoc
@@ -104,6 +104,7 @@ https://github.com/elastic/beats/compare/v8.2.0\...main[Check the HEAD diff]
 
 *Packetbeat*
 
+- Fix panic on memcache transaction with no request or response. {issue}33852[33852] {pull}33853[33853]
 
 *Winlogbeat*
 
diff --git a/packetbeat/protos/memcache/memcache.go b/packetbeat/protos/memcache/memcache.go
index 4668c8154b16..aa38b031ebd7 100644
--- a/packetbeat/protos/memcache/memcache.go
+++ b/packetbeat/protos/memcache/memcache.go
@@ -198,6 +198,9 @@ func (mc *memcache) GetPorts() []int {
 }
 
 func (mc *memcache) finishTransaction(t *transaction) error {
+	if t == nil {
+		return nil
+	}
 	mc.handler.onTransaction(t)
 	return nil
 }
diff --git a/packetbeat/protos/memcache/plugin_udp.go b/packetbeat/protos/memcache/plugin_udp.go
index e58387eda1ed..dc60b218844a 100644
--- a/packetbeat/protos/memcache/plugin_udp.go
+++ b/packetbeat/protos/memcache/plugin_udp.go
@@ -144,6 +144,7 @@ func (mc *memcache) ParseUDP(pkt *protos.Packet) {
 	}
 	if !done {
 		trans.timer = time.AfterFunc(mc.udpConfig.transTimeout, func() {
+			defer logp.Recover("ParseMemcache(UDP) panic during forward")
 			debug("transaction timeout -> forward")
 			mc.onUDPTrans(trans)
 			mc.udpExpTrans.push(trans)
@@ -261,6 +262,9 @@ func (c *udpConnection) killTransaction(t *udpTransaction) {
 }
 
 func (lst *udpExpTransList) push(t *udpTransaction) {
+	if t == nil {
+		return
+	}
 	lst.Lock()
 	defer lst.Unlock()
 	t.next = lst.head