[Samba] Flooding Samba DC with random requests

Julian Zielke jzielke at next-level-integration.com
Tue Apr 25 12:07:35 UTC 2017


our virtual DCs specs are:

System is running on iSCSI Storage in an Openstack Enviroment.

Smb.conf on our DC 03 and 04:
# Global parameters
        workgroup = NLI
        realm = nli.local
        netbios name = dc04
        server role = active directory domain controller
        allow dns updates = nonsecure
        dns forwarder = xxx.xxx.xxx.xxx
        ldap server require strong auth = no

        path = /var/lib/samba/sysvol/nli.local/scripts
        read only = No

        path = /var/lib/samba/sysvol
        read only = Yes

Smb.conf on our clients:
#Ansible managed
# global options
  workgroup = NLI
  realm = NLI.LOCAL
  netbios name = xxxxxx
  server string = Samba AD Client Version %v
  security = ads
  password server = dc3.nli.local, dc4.nli.local, dc2.nli.local, dc1.nli.local, *
  server role = member server
  socket options = TCP_NODELAY SO_KEEPALIVE=4
  deadtime = 15

# winbind options
  winbind enum users = yes
  winbind enum groups = yes
  winbind refresh tickets = yes
  winbind offline logon = true
  winbind nested groups = yes
  winbind use default domain = yes
  winbind cache time = 300

  winbind nss info = template
  template shell = /bin/bash
  template homedir = /home/NLI.LOCAL/%U

# local user id mapping
  idmap config * : backend = tdb
  idmap config * : range = 3000-7999

# domain user id mapping
  idmap config NLI : backend = rid
  idmap config NLI : range = 10000-999999

# log configuration
  log file = /var/log/samba/log.%m
  log level = 1
  max log size = 1000

# root to domain admin mapping
  username map = /etc/samba/user.map

Dc03 and dc04 in our cloud replicate to our dc01 and dc02 in our HQ.

- Julian

-----Ursprüngliche Nachricht-----
Von: Andrew Bartlett [mailto:abartlet at samba.org]
Gesendet: Dienstag, 25. April 2017 11:45
An: Julian Zielke <jzielke at next-level-integration.com>; samba at lists.samba.org
Betreff: Re: [Samba] Flooding Samba DC with random requests

On Tue, 2017-04-25 at 09:05 +0000, Julian Zielke via samba wrote:
> Hi,
> yesterday we experienced a heavy request flooding from multiple
> servers being a domain member against our Samba Sernet DCs.
> All those servers are domain members and allow login using PAM
> (Samba+Winbind).

Currently we only have one process handling the LDAP traffic, which would explain why a traffic flood like this:

> Running TCPDump we had like 400 Requests per 5 seconds like this:


Still only gives busy CPU, but not I/O wait:

> Due to that flooding, even logins via ssh on our servers timed out.
> CPU Load on both DCs went up to 95% without high I/O wait.
> After restarting the sernet-samba-ad service on both DCs, the Problem
> went away.

My first guess is that the multiple connections caused timeouts on the clients, causing the clients to reconnect and try again, magnifying the load.  However it is really hard to tell with the limited information provided.

I'm working to make our LDAP server multi-process, more efficient and able to use all the available CPUs.

Andrew Bartlett
Andrew Bartlett                       http://samba.org/~abartlet/
Authentication Developer, Samba Team  http://samba.org
Samba Developer, Catalyst IT          http://catalyst.net.nz/services/samba

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