[Samba] protocol between pam/nss & winbindd

[Jonathon Reinhart]

Hi Michael,

Your question is perfectly clear to me. I'm no expert, but I believe
the local winbind protocol is bitness-agnostic, but uses "host-native"
byte order. I took a look through the code, and this is what I found:

pam_winbind [1] links against libwbclient [2] (libwbclient.so.0 on
Debian). The winbind request protocol is defined by "struct
winbindd_request" [3] which has this big warning:

    This structure MUST be the same size in the 32bit and 64bit builds
    for compatibility between /lib64/libnss_winbind.so and
    /lib/libnss_winbind.so

    DO NOT CHANGE THIS STRUCTURE WITHOUT TESTING THE 32BIT NSS LIB
    AGAINST A 64BIT WINBINDD    --jerry

Jerry sounds pretty serious about 32 / 64 bit compatibility!

What I don't see, however, are any ntoh[sl] or hton[sl] calls, or
comments about byteorder. winbindd_init_request() sets integer fields
directly. [4]

This is not at all surprising; I'm not aware of any UNIX socket
protocols that bother with byte order, because it is assumed that
you'll always be talking to a process on the same host which must use
the same byte order -- except for your interesting, but somewhat
contrived example of emulating a processor that uses a different byte
order. Fortunately, ARMv7 and x86 are both little-endian, so that
shouldn't be a problem for you.

Good luck! Hope this helps.

Jonathon

[1]: https://gitlab.com/samba-team/samba/-/blob/samba-4.9.5/nsswitch/pam_winbind.c
[2]: https://gitlab.com/samba-team/samba/-/tree/samba-4.9.5/nsswitch/libwbclient
[3]: https://gitlab.com/samba-team/samba/-/blob/samba-4.9.5/nsswitch/winbind_struct_protocol.h#L236-244
[4]: https://gitlab.com/samba-team/samba/-/blob/samba-4.9.5/nsswitch/wb_common.c#L59-62



On Wed, Jun 1, 2022 at 5:12 AM Michael Tokarev via samba
<samba at lists.samba.org> wrote:
>
> Hi!
>
> Is the (local) protocol between pam_winbind, nss_winbind
> and winbindd architecture-agnostic, like, using network
> types and network byte order, or is it architecture-dependent?
>
> I mean, for example, on a bi-arch machine (i386 & x86_64), will
> single winbindd serve both 32 and 64 bit clients fine?
>
> Will it work if I run, say, armhf binary with armhf nss_winbind
> on the same machine with qemu-user-arm emulation, - will x86_64
> winbindd understand armhf client and reply to it correctly?
>
> Thanks,
>
> /mjt
>
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