From 37997f7e9a694715c764528567e569812fa3066a Mon Sep 17 00:00:00 2001
From: "Richard W.M. Jones" <rjones@redhat.com>
Date: Thu, 14 Dec 2023 08:34:56 +0000
Subject: [PATCH 2/2] ocaml: Nullify custom block before releasing runtime lock

Avoids a potential, though if possible then very rare, double free
path.

Suggested-by: Guillaume Munch-Maccagnoni
See: https://github.com/ocaml/ocaml/issues/12820
---
 ocaml/handle.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/ocaml/handle.c b/ocaml/handle.c
index 0e809c6f0d..8d8a632fef 100644
--- a/ocaml/handle.c
+++ b/ocaml/handle.c
@@ -54,12 +54,12 @@ nbd_internal_ocaml_nbd_close (value hv)
   struct nbd_handle *h = NBD_val (hv);
 
   if (h) {
+    /* So we don't double-free. */
+    NBD_val (hv) = NULL;
+
     caml_enter_blocking_section ();
     nbd_close (h);
     caml_leave_blocking_section ();
-
-    /* So we don't double-free. */
-    NBD_val (hv) = NULL;
   }
 
   CAMLreturn (Val_unit);
-- 
2.43.0