From 0e8fd182deb37cdba972c43ee738bd82948cf9fa Mon Sep 17 00:00:00 2001
From: Nimrod Gileadi <nimrod@google.com>
Date: Thu, 4 Aug 2022 09:58:42 -0700
Subject: [PATCH] Ensure that mjModel->nbody is never zero.

nbody is already checked to be non-negative, but various pieces of code assume it's nonzero (because there's always a world body).

PiperOrigin-RevId: 465339241
Change-Id: I38ce3764074d03bf9a703aa490964c1eb83cc1da
---
 src/engine/engine_io.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/src/engine/engine_io.c b/src/engine/engine_io.c
index f6023c8b..010ea6a7 100644
--- a/src/engine/engine_io.c
+++ b/src/engine/engine_io.c
@@ -462,6 +462,13 @@ mjModel* mj_makeModel(int nq, int nv, int nu, int na, int nbody, int njnt,
   MJMODEL_INTS;
 #undef X
 
+  // nbody should always be positive
+  if (m->nbody == 0) {
+    mju_warning("Invalid model: nbody == 0");
+    mj_deleteModel(m);
+    return 0;
+  }
+
   // compute buffer size
   m->nbuffer = 0;
 #define X(type, name, nr, nc)                                                \