[Samba] rpcd_lsad core dump

[Nick Couchman]

Hello, everyone,
I started seeing an issue over the weekend where one of my Samba
servers that has been running fine for quite some time started seeing
segfaults on the rpcd_lsad daemon, causing Winbind authentications to
fail and, thus, SMB shares to be unavailable. The stack traces look
like this:

Stack trace of thread 1539:
#0  0x00007ff1c61bca4f raise (libc.so.6)
#1  0x00007ff1c618fdb5 abort (libc.so.6)
#2  0x00007ff1c75b52c4 dump_core (libsmbconf.so.0)
#3  0x00007ff1c75c2a70 smb_panic_s3 (libsmbconf.so.0)
#4  0x00007ff1c7c31a1e smb_panic (/usr/lib64/libsamba-util.so.0.0.1)
#5  0x00007ff1c797c405 set_unix_security_ctx (libsmbd-base-samba4.so)
#6  0x00007ff1c797c61d set_sec_ctx_internal (libsmbd-base-samba4.so)
#7  0x00007ff1c797cd3b set_root_sec_ctx (libsmbd-base-samba4.so)
#8  0x00007ff1c7ada8c6 xid_to_sid (/usr/lib64/libsamba-passdb.so.0.28.0)
#9  0x00007ff1c7adabeb gid_to_sid (/usr/lib64/libsamba-passdb.so.0.28.0)
#10 0x00007ff1c7b6e189 add_local_groups (/usr/lib64/samba/libauth-samba4.so)
#11 0x00007ff1c7b6f175 create_local_nt_token_from_info3
(/usr/lib64/samba/libauth-samba4.so)
#12 0x00007ff1c7b683af create_local_token.part.2
(/usr/lib64/samba/libauth-samba4.so)
#13 0x00007ff1c7b6a187 make_new_session_info_guest.constprop.6
(/usr/lib64/samba/libauth-samba4.so)
#14 0x00007ff1c7b6a470 init_guest_session_info
(/usr/lib64/samba/libauth-samba4.so)
#15 0x00007ff1c7ca629d rpc_worker_main
(/usr/lib64/samba/libRPC-WORKER-samba4.so)
#16 0x000056236e8e6a90 main (rpcd_lsad)
#17 0x00007ff1c61a8ca3 __libc_start_main (libc.so.6)
#18 0x000056236e8e6ace _start (rpcd_lsad)

In troubleshooting the issue, I disabled SELinux on the system, and
the issue seems to have gone away - it's just strange that it showed
up seemingly out of nowhere. I also have other systems running Samba
with SELinux enabled, and haven't seen those issues pop up anywhere
else (yet).

Environment is:
* CentOS Stream 8
* 4.18.0-394.el8.x86_64
* Samba 4.16.2
* Active Directory at functional level 2012, with 2012-2019 servers

Anyone seen any similar issues, or any hints as to what may be going
on? Let me know if I can provide any more detail.

-Nick