samba-tool domain join segfaults (4.16)

[Michael Tokarev]

Hi!

I'm facing a segfault in samba-tool when doing domain join, in
source3/utils/py_net.c py_net_join_member(). Here it is (with some
omissions for brevity):

static PyObject *py_net_join_member(py_net_Object *self, PyObject *args, PyObject *kwargs)
{
         struct libnet_JoinCtx *r = NULL;
...
         werr = libnet_init_JoinCtx(mem_ctx, &r);   <= here, &r is initialized okay
        // r = (struct libnet_JoinCtx *) 0xa5f850

...
         // but after this call: r becomes.. NULL.
         if (!PyArg_ParseTupleAndKeywords(args, kwargs, "|sssssszpp:Join",
                                          discard_const_p(char *, kwnames),
                                          &r->in.dnshostname,
                                          &r->in.upn,
                                          &r->in.account_ou,
                                          &r->in.os_name,
                                          &r->in.os_version,
                                          &r->in.os_servicepack,
                                          &r->in.machine_password,
                                          &r->in.debug,
                                          &no_dns_updates)) {
                 talloc_free(mem_ctx);
                 PyErr_FromString(_("Invalid arguments\n"));
                 return NULL;
         }
         // r = (struct libnet_JoinCtx *) 0x0
...
         // and here, it gets a segfault.
         r->in.domain_name       = lpcfg_realm(self->lp_ctx);
         r->in.domain_name_type  = JoinDomNameTypeDNS;

Unfortunately I don't know how to print *args and *kwargs there.
They're PyTuple_Type and PyDict_Type, respectively.

The backtrace:

BACKTRACE: 36 stack frames:
  #0 /lib/x86_64-linux-gnu/libsamba-util.so.0(log_stack_trace+0x30) [0x7ffff70510f0]
  #1 /lib/x86_64-linux-gnu/libsamba-util.so.0(smb_panic+0x9) [0x7ffff7051339]
  #2 /lib/x86_64-linux-gnu/libsamba-util.so.0(+0xf3d1) [0x7ffff70513d1]
  #3 /lib/x86_64-linux-gnu/libpthread.so.0(+0x14140) [0x7ffff7fad140]
  #4 /usr/lib/python3/dist-packages/samba/net_s3.cpython-39-x86_64-linux-gnu.so(+0x7558) [0x7ffff221c558]
  #5 /usr/bin/python3() [0x53f350]
  #6 /usr/bin/python3(_PyObject_MakeTpCall+0x39b) [0x51d89b]
  #7 /usr/bin/python3(_PyEval_EvalFrameDefault+0x5f7f) [0x517a0f]
  #8 /usr/bin/python3() [0x5106ed]
  #9 /usr/bin/python3(_PyFunction_Vectorcall+0x361) [0x528d21]
  #10 /usr/bin/python3() [0x53bcfb]
  #11 /usr/bin/python3(PyObject_Call+0xc1) [0x53c361]
  #12 /usr/bin/python3(_PyEval_EvalFrameDefault+0x23fb) [0x513e8b]
  #13 /usr/bin/python3() [0x5106ed]
  #14 /usr/bin/python3(_PyFunction_Vectorcall+0x361) [0x528d21]
  #15 /usr/bin/python3() [0x53be7e]
  #16 /usr/bin/python3(_PyEval_EvalFrameDefault+0x23fb) [0x513e8b]
  #17 /usr/bin/python3() [0x5106ed]
  #18 /usr/bin/python3(_PyFunction_Vectorcall+0x361) [0x528d21]
  #19 /usr/bin/python3() [0x53be7e]
  #20 /usr/bin/python3(_PyEval_EvalFrameDefault+0x23fb) [0x513e8b]
  #21 /usr/bin/python3() [0x5106ed]
  #22 /usr/bin/python3(_PyFunction_Vectorcall+0x361) [0x528d21]
  #23 /usr/bin/python3() [0x53be7e]
  #24 /usr/bin/python3(_PyEval_EvalFrameDefault+0x23fb) [0x513e8b]
  #25 /usr/bin/python3() [0x5106ed]
  #26 /usr/bin/python3(_PyEval_EvalCodeWithName+0x47) [0x510497]
  #27 /usr/bin/python3(PyEval_EvalCode+0x23) [0x5f5be3]
  #28 /usr/bin/python3() [0x619de7]
  #29 /usr/bin/python3() [0x615610]
  #30 /usr/bin/python3() [0x619d79]
  #31 /usr/bin/python3(PyRun_SimpleFileExFlags+0x196) [0x619816]
  #32 /usr/bin/python3(Py_RunMain+0x2b3) [0x60d4e3]
  #33 /usr/bin/python3(Py_BytesMain+0x29) [0x5ea6e9]
  #34 /lib/x86_64-linux-gnu/libc.so.6(__libc_start_main+0xea) [0x7ffff7c5dd0a]
  #35 /usr/bin/python3(_start+0x2a) [0x5ea5ea]

Here's what I'm doing: it is a new host, with fresh samba 4.16 install
(debian build), the command:

  samba-tool domain join tls.msk.ru MEMBER -U mjt-adm

and here's the smb.conf's global section:

[global]
         dedicated keytab file = /etc/krb5.keytab
         disable spoolss = Yes
         kerberos method = secrets and keytab
         netbios name = WH
         realm = TLS.MSK.RU
         security = ADS
         server role = member server
         winbind use default domain = Yes
         workgroup = TLS

How to print the python types in gdb?

Thanks,

/mjt