[Libguestfs] [libnbd PATCH] python: Plug some memory leaks on error paths
Eric Blake
eblake at redhat.com
Tue Sep 8 23:11:00 UTC 2020
Inspection of the generated code showed several places where we did
not release references on all error paths. In particular, switching
things to always jump to an out: label, even when the underlying C
function cannot fail, makes it easier to clean up when the user passes
wrong types to a function call.
One of the easiest triggers without this patch was this one-liner:
$ nbdsh -c 'h.block_status(512, 0, 1)'
which fails due to '1' not being callable, but leaked malloc'd memory
in the process.
---
generator/Python.ml | 55 +++++++++++++++++++++++++++++----------------
1 file changed, 36 insertions(+), 19 deletions(-)
diff --git a/generator/Python.ml b/generator/Python.ml
index 4a96cf6..9a22f9e 100644
--- a/generator/Python.ml
+++ b/generator/Python.ml
@@ -177,6 +177,7 @@ let print_python_closure_wrapper { cbname; cbargs } =
pr " Py_DECREF (py_%s_modname);\n" n;
pr " if (!py_%s_mod) { PyErr_PrintEx (0); return -1; }\n" n;
pr " PyObject *py_%s = PyObject_CallMethod (py_%s_mod, \"c_int\", \"i\", *%s);\n" n n n;
+ pr " Py_DECREF (py_%s_mod);\n" n;
pr " if (!py_%s) { PyErr_PrintEx (0); return -1; }\n" n;
| CBString _
| CBUInt _
@@ -263,7 +264,7 @@ let print_python_binding name { args; optargs; ret; may_set_error } =
pr " PyObject *py_h;\n";
pr " struct nbd_handle *h;\n";
pr " %s ret;\n" (C.type_of_ret ret);
- pr " PyObject *py_ret;\n";
+ pr " PyObject *py_ret = NULL;\n";
List.iter (
function
| Bool n -> pr " int %s;\n" n
@@ -279,7 +280,7 @@ let print_python_binding name { args; optargs; ret; may_set_error } =
pr " struct py_aio_buffer *%s_buf;\n" n
| Closure { cbname } ->
pr " struct user_data *%s_user_data = alloc_user_data ();\n" cbname;
- pr " if (%s_user_data == NULL) return NULL;\n" cbname;
+ pr " if (%s_user_data == NULL) goto out;\n" cbname;
pr " nbd_%s_callback %s = { .callback = %s_wrapper,\n"
cbname cbname cbname;
pr " .user_data = %s_user_data,\n" cbname;
@@ -316,7 +317,7 @@ let print_python_binding name { args; optargs; ret; may_set_error } =
function
| OClosure { cbname } ->
pr " struct user_data *%s_user_data = alloc_user_data ();\n" cbname;
- pr " if (%s_user_data == NULL) return NULL;\n" cbname;
+ pr " if (%s_user_data == NULL) goto out;\n" cbname;
pr " nbd_%s_callback %s = { .callback = %s_wrapper,\n"
cbname cbname cbname;
pr " .user_data = %s_user_data,\n" cbname;
@@ -382,7 +383,7 @@ let print_python_binding name { args; optargs; ret; may_set_error } =
| OFlags (n, _) -> pr ", &%s" n
) optargs;
pr "))\n";
- pr " return NULL;\n";
+ pr " goto out;\n";
pr " h = get_handle (py_h);\n";
List.iter (
@@ -395,12 +396,13 @@ let print_python_binding name { args; optargs; ret; may_set_error } =
pr " %s_buf = nbd_internal_py_get_aio_buffer (%s);\n" n n
| Closure { cbname } ->
pr " /* Increment refcount since pointer may be saved by libnbd. */\n";
- pr " Py_INCREF (%s_user_data->fn);\n" cbname;
pr " if (!PyCallable_Check (%s_user_data->fn)) {\n" cbname;
pr " PyErr_SetString (PyExc_TypeError,\n";
pr " \"callback parameter %s is not callable\");\n" cbname;
- pr " return NULL;\n";
- pr " }\n"
+ pr " %s_user_data->fn = NULL;\n" cbname;
+ pr " goto out;\n";
+ pr " }\n";
+ pr " Py_INCREF (%s_user_data->fn);\n" cbname
| Enum _ -> ()
| Flags (n, _) -> pr " %s_u32 = %s;\n" n n
| Fd _ | Int _ -> ()
@@ -413,7 +415,7 @@ let print_python_binding name { args; optargs; ret; may_set_error } =
| String _ -> ()
| StringList n ->
pr " %s = nbd_internal_py_get_string_list (py_%s);\n" n n;
- pr " if (!%s) { py_ret = NULL; goto out; }\n" n
+ pr " if (!%s) goto out;\n" n
| UInt _ -> ()
| UInt32 n -> pr " %s_u32 = %s;\n" n n
| UInt64 n -> pr " %s_u64 = %s;\n" n n
@@ -423,12 +425,13 @@ let print_python_binding name { args; optargs; ret; may_set_error } =
| OClosure { cbname } ->
pr " if (%s_user_data->fn != Py_None) {\n" cbname;
pr " /* Increment refcount since pointer may be saved by libnbd. */\n";
- pr " Py_INCREF (%s_user_data->fn);\n" cbname;
pr " if (!PyCallable_Check (%s_user_data->fn)) {\n" cbname;
pr " PyErr_SetString (PyExc_TypeError,\n";
pr " \"callback parameter %s is not callable\");\n" cbname;
- pr " return NULL;\n";
+ pr " %s_user_data->fn = NULL;\n" cbname;
+ pr " goto out;\n";
pr " }\n";
+ pr " Py_INCREF (%s_user_data->fn);\n" cbname;
pr " }\n";
pr " else\n";
pr " %s.callback = NULL; /* we're not going to call it */\n" cbname
@@ -447,7 +450,8 @@ let print_python_binding name { args; optargs; ret; may_set_error } =
pr " Py_INCREF (%s);\n" n;
pr " completion_user_data->buf = %s;\n" n;
| _ -> ()
- ) args;
+ ) args;
+ pr "\n";
(* Call the underlying C function. *)
pr " ret = nbd_%s (h" name;
@@ -477,11 +481,20 @@ let print_python_binding name { args; optargs; ret; may_set_error } =
| OFlags (n, _) -> pr ", %s_u32" n
) optargs;
pr ");\n";
+ List.iter (
+ function
+ | Closure { cbname } -> pr " %s_user_data = NULL;\n" cbname
+ | _ -> ()
+ ) args;
+ List.iter (
+ function
+ | OClosure { cbname } -> pr " %s_user_data = NULL;\n" cbname
+ | _ -> ()
+ ) optargs;
if may_set_error then (
pr " if (ret == %s) {\n"
(match C.errcode_of_ret ret with Some s -> s | None -> assert false);
pr " raise_exception ();\n";
- pr " py_ret = NULL;\n";
pr " goto out;\n";
pr " }\n"
);
@@ -529,14 +542,14 @@ let print_python_binding name { args; optargs; ret; may_set_error } =
);
pr "\n";
- if may_set_error then
- pr " out:\n";
+ pr " out:\n";
List.iter (
function
| Bool _ -> ()
| BytesIn (n, _) -> pr " PyBuffer_Release (&%s);\n" n
| BytesPersistIn _ | BytesOut _ | BytesPersistOut _ -> ()
- | Closure _ -> ()
+ | Closure { cbname } ->
+ pr " if (%s_user_data) free_user_data (%s_user_data);\n" cbname cbname
| Enum _ -> ()
| Flags _ -> ()
| Fd _ | Int _ -> ()
@@ -550,6 +563,12 @@ let print_python_binding name { args; optargs; ret; may_set_error } =
| UInt32 _ -> ()
| UInt64 _ -> ()
) args;
+ List.iter (
+ function
+ | OClosure { cbname } ->
+ pr " if (%s_user_data) free_user_data (%s_user_data);\n" cbname cbname
+ | OFlags _ -> ()
+ ) optargs;
pr " return py_ret;\n";
pr "}\n";
pr "\n"
@@ -594,10 +613,8 @@ let generate_python_methods_c () =
pr "{\n";
pr " struct user_data *data = user_data;\n";
pr "\n";
- pr " if (data->fn != NULL)\n";
- pr " Py_DECREF (data->fn);\n";
- pr " if (data->buf != NULL)\n";
- pr " Py_DECREF (data->buf);\n";
+ pr " Py_XDECREF (data->fn);\n";
+ pr " Py_XDECREF (data->buf);\n";
pr " free (data);\n";
pr "}\n";
pr "\n";
--
2.28.0
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