From 9f52ab7794bf54169139995c5296aa5f39e47706 Mon Sep 17 00:00:00 2001
From: "Richard W.M. Jones" <rjones@redhat.com>
Date: Thu, 14 Dec 2023 08:33:10 +0000
Subject: [PATCH] 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
(cherry picked from commit e93fd7e8acf34192c0d1b70611e3474dde346941)
---
 ocaml/guestfs-c.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/ocaml/guestfs-c.c b/ocaml/guestfs-c.c
index 700c33ab..ea9a0598 100644
--- a/ocaml/guestfs-c.c
+++ b/ocaml/guestfs-c.c
@@ -156,6 +156,9 @@ guestfs_int_ocaml_close (value gv)
     size_t len;
     value **roots = get_all_event_callbacks (g, &len);
 
+    /* So we don't double-free. */
+    Guestfs_val (gv) = NULL;
+
     /* Close the handle: this could invoke callbacks from the list
      * above, which is why we don't want to delete them before
      * closing the handle.
@@ -173,9 +176,6 @@ guestfs_int_ocaml_close (value gv)
       }
       free (roots);
     }
-
-    /* So we don't double-free. */
-    Guestfs_val (gv) = NULL;
   }
 
   CAMLreturn (Val_unit);