[PATCH] tools/ocaml/libs: Fix memory/resource leaks with caml_alloc_custom()

[Andrew Cooper]

All caml_alloc_*() functions can throw exceptions, and longjump out of
context.  If this happens, we leak the xch/xce handle.

Reorder the logic to allocate the the Ocaml object first.

Fixes: 8b3c06a3e545 ("tools/ocaml/xenctrl: OCaml 5 support, fix use-after-free")
Fixes: 22d5affdf0ce ("tools/ocaml/evtchn: OCaml 5 support, fix potential 
resource leak")
Signed-off-by: Andrew Cooper <andrew.coop...@citrix.com>
---
CC: Christian Lindig <christian.lin...@citrix.com>
CC: David Scott <d...@recoil.org>
CC: Edwin Török <edwin.to...@cloud.com>
CC: Rob Hoes <rob.h...@citrix.com>
---
 tools/ocaml/libs/eventchn/xeneventchn_stubs.c | 6 ++++--
 tools/ocaml/libs/xc/xenctrl_stubs.c           | 3 ++-
 2 files changed, 6 insertions(+), 3 deletions(-)

diff --git a/tools/ocaml/libs/eventchn/xeneventchn_stubs.c 
b/tools/ocaml/libs/eventchn/xeneventchn_stubs.c
index 34dcfed30275..1980acf405a5 100644
--- a/tools/ocaml/libs/eventchn/xeneventchn_stubs.c
+++ b/tools/ocaml/libs/eventchn/xeneventchn_stubs.c
@@ -63,6 +63,8 @@ CAMLprim value stub_eventchn_init(value cloexec)
        if ( !Bool_val(cloexec) )
                flags |= XENEVTCHN_NO_CLOEXEC;
 
+       result = caml_alloc_custom(&xenevtchn_ops, sizeof(xce), 0, 1);
+
        caml_enter_blocking_section();
        xce = xenevtchn_open(NULL, flags);
        caml_leave_blocking_section();
@@ -70,7 +72,6 @@ CAMLprim value stub_eventchn_init(value cloexec)
        if (xce == NULL)
                caml_failwith("open failed");
 
-       result = caml_alloc_custom(&xenevtchn_ops, sizeof(xce), 0, 1);
        *(xenevtchn_handle **)Data_custom_val(result) = xce;
 
        CAMLreturn(result);
@@ -82,6 +83,8 @@ CAMLprim value stub_eventchn_fdopen(value fdval)
        CAMLlocal1(result);
        xenevtchn_handle *xce;
 
+       result = caml_alloc_custom(&xenevtchn_ops, sizeof(xce), 0, 1);
+
        caml_enter_blocking_section();
        xce = xenevtchn_fdopen(NULL, Int_val(fdval), 0);
        caml_leave_blocking_section();
@@ -89,7 +92,6 @@ CAMLprim value stub_eventchn_fdopen(value fdval)
        if (xce == NULL)
                caml_failwith("evtchn fdopen failed");
 
-       result = caml_alloc_custom(&xenevtchn_ops, sizeof(xce), 0, 1);
        *(xenevtchn_handle **)Data_custom_val(result) = xce;
 
        CAMLreturn(result);
diff --git a/tools/ocaml/libs/xc/xenctrl_stubs.c 
b/tools/ocaml/libs/xc/xenctrl_stubs.c
index f9006c662382..ed1cbafdb488 100644
--- a/tools/ocaml/libs/xc/xenctrl_stubs.c
+++ b/tools/ocaml/libs/xc/xenctrl_stubs.c
@@ -98,6 +98,8 @@ CAMLprim value stub_xc_interface_open(value unit)
        CAMLlocal1(result);
        xc_interface *xch;
 
+       result = caml_alloc_custom(&xenctrl_ops, sizeof(xch), 0, 1);
+
        caml_enter_blocking_section();
        xch = xc_interface_open(NULL, NULL, 0);
        caml_leave_blocking_section();
@@ -105,7 +107,6 @@ CAMLprim value stub_xc_interface_open(value unit)
        if ( !xch )
                failwith_xc(xch);
 
-       result = caml_alloc_custom(&xenctrl_ops, sizeof(xch), 0, 1);
        *(xc_interface **)Data_custom_val(result) = xch;
 
        CAMLreturn(result);
-- 
2.11.0