Fixes for https://github.com/ocaml/ocaml/issues/12820

0001-ocaml-Use-Gc.finalize-instead-of-a-C-finalizer.patch

@@ -0,0 +1,106 @@
+From db48794fa89547a4799b832331e82b4b8b98f03d Mon Sep 17 00:00:00 2001
+From: "Richard W.M. Jones" <rjones@redhat.com>
+Date: Wed, 13 Dec 2023 22:32:12 +0000
+Subject: [PATCH 1/2] ocaml: Use Gc.finalize instead of a C finalizer
+
+Since OCaml 5.1.1, C finalizers no longer allow calling
+caml_enter_blocking_section.  They are relatively inflexible compared
+to registering an OCaml finalizer (Gc.finalize) to call NBD.close, so
+use that instead.
+
+I didn't replace NBD.Buffer which still uses a C finalizer.  This one
+doesn't call caml_enter_blocking_section.
+
+Suggested-by: Guillaume Munch-Maccagnoni
+See: https://github.com/ocaml/ocaml/issues/12820
+---
+ generator/OCaml.ml |  7 ++++++-
+ ocaml/handle.c     | 21 ++++++++-------------
+ ocaml/nbd-c.h      |  3 +--
+ 3 files changed, 15 insertions(+), 16 deletions(-)
+
+diff --git a/generator/OCaml.ml b/generator/OCaml.ml
+index 095a31df27..4d8501b518 100644
+--- a/generator/OCaml.ml
++++ b/generator/OCaml.ml
+@@ -343,9 +343,14 @@ let
+ 
+ type t
+ 
+-external create : unit -> t = \"nbd_internal_ocaml_nbd_create\"
++external _create : unit -> t = \"nbd_internal_ocaml_nbd_create\"
+ external close : t -> unit = \"nbd_internal_ocaml_nbd_close\"
+ 
++let create () =
++  let nbd = _create () in
++  Gc.finalise close nbd;
++  nbd
++
+ let with_handle f =
+   let nbd = create () in
+   try let r = f nbd in close nbd; r with exn -> close nbd; raise exn
+diff --git a/ocaml/handle.c b/ocaml/handle.c
+index b3e5a0fc33..0e809c6f0d 100644
+--- a/ocaml/handle.c
++++ b/ocaml/handle.c
+@@ -32,16 +32,6 @@
+ 
+ #include "nbd-c.h"
+ 
+-void
+-nbd_internal_ocaml_handle_finalize (value hv)
+-{
+-  struct nbd_handle *h = NBD_val (hv);
+-
+-  caml_enter_blocking_section ();
+-  nbd_close (h);
+-  caml_leave_blocking_section ();
+-}
+-
+ value
+ nbd_internal_ocaml_nbd_create (value unitv)
+ {
+@@ -61,11 +51,16 @@ value
+ nbd_internal_ocaml_nbd_close (value hv)
+ {
+   CAMLparam1 (hv);
++  struct nbd_handle *h = NBD_val (hv);
+ 
+-  nbd_internal_ocaml_handle_finalize (hv);
++  if (h) {
++    caml_enter_blocking_section ();
++    nbd_close (h);
++    caml_leave_blocking_section ();
+ 
+-  /* So we don't double-free in the finalizer. */
+-  NBD_val (hv) = NULL;
++    /* So we don't double-free. */
++    NBD_val (hv) = NULL;
++  }
+ 
+   CAMLreturn (Val_unit);
+ }
+diff --git a/ocaml/nbd-c.h b/ocaml/nbd-c.h
+index adcdd15aa8..134c3a1608 100644
+--- a/ocaml/nbd-c.h
++++ b/ocaml/nbd-c.h
+@@ -54,7 +54,6 @@ caml_alloc_initialized_string (mlsize_t len, const char *p)
+ }
+ #endif
+ 
+-extern void nbd_internal_ocaml_handle_finalize (value);
+ extern void nbd_internal_ocaml_buffer_finalize (value);
+ 
+ extern void nbd_internal_ocaml_raise_error (void) Noreturn;
+@@ -72,7 +71,7 @@ extern void nbd_internal_ocaml_exception_in_wrapper (const char *, value);
+ 
+ static struct custom_operations libnbd_custom_operations = {
+   "libnbd_custom_operations",
+-  nbd_internal_ocaml_handle_finalize,
++  custom_finalize_default,
+   custom_compare_default,
+   custom_hash_default,
+   custom_serialize_default,
+-- 
+2.43.0
+

0002-ocaml-Nullify-custom-block-before-releasing-runtime-.patch

@@ -0,0 +1,37 @@
+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
+

libnbd.spec

@@ -9,7 +9,7 @@
 
 Name:           libnbd
 Version:        1.19.2
-Release:        2%{?dist}
+Release:        3%{?dist}
 Summary:        NBD client library in userspace
 
 License:        LGPL-2.0-or-later AND BSD-3-Clause
@@ -25,6 +25,10 @@ Source2:       libguestfs.keyring
 # Maintainer script which helps with handling patches.
 Source3:        copy-patches.sh
 
+# Fixes for https://github.com/ocaml/ocaml/issues/12820
+Patch: 0001-ocaml-Use-Gc.finalize-instead-of-a-C-finalizer.patch
+Patch: 0002-ocaml-Nullify-custom-block-before-releasing-runtime-.patch
+
 %if 0%{patches_touch_autotools}
 BuildRequires: autoconf, automake, libtool
 %endif
@@ -375,6 +379,9 @@ make %{?_smp_mflags} check || {
 
 
 %changelog
+* Thu Dec 14 2023 Richard W.M. Jones <rjones@redhat.com> - 1.19.2-3
+- Fixes for https://github.com/ocaml/ocaml/issues/12820
+
 * Tue Dec 12 2023 Richard W.M. Jones <rjones@redhat.com> - 1.19.2-2
 - OCaml 5.1.1 rebuild for Fedora 40