From 82ae3fe63528e475b8547a72853a17fa47c08bd7 Mon Sep 17 00:00:00 2001
From: Andrew Tridgell <andrew@tridgell.net>
Date: Sat, 14 Nov 2020 14:09:24 +1100
Subject: [PATCH] AP_NavEKF3: fixed memory corruption on push before init

this fixes a bug that happens with VISION_SPEED_ESTIMATE from a
companion computer, which may come in before the EKF buffers are
allocated. That causes a push to an uninitialised ringbuffer which
triggers memory corruption

found using the new memory guard system
---
 libraries/AP_NavEKF3/AP_NavEKF3_Buffer.h | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/libraries/AP_NavEKF3/AP_NavEKF3_Buffer.h b/libraries/AP_NavEKF3/AP_NavEKF3_Buffer.h
index 327e361935..6672fe4a88 100644
--- a/libraries/AP_NavEKF3/AP_NavEKF3_Buffer.h
+++ b/libraries/AP_NavEKF3/AP_NavEKF3_Buffer.h
@@ -85,6 +85,9 @@ public:
     */
     inline void push(element_type element)
     {
+        if (buffer == nullptr) {
+            return;
+        }
         // Advance head to next available index
         _head = (_head+1)%_size;
         // New data is written at the head