[Samba] Flooding Samba DC with random requests

[Julian Zielke]

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).

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

tcpdump -i eth0 dst port 389
tcpdump: verbose output suppressed, use -v or -vv for full protocol decode
listening on eth0, link-type EN10MB (Ethernet), capture size 262144 bytes
10:43:14.195984 IP hostname.nli.local.38153 > dc.ldap: Flags [P.], seq 3322715177:3322715340, ack 2230642521, win 1444, options [nop,nop,TS val 54690397 ecr 19378130], length 163
10:43:14.199632 IP hostname.nli.local.38153 > dc.ldap: Flags [P.], seq 163:353, ack 91, win 1444, options [nop,nop,TS val 54690398 ecr 19455846], length 190
10:43:14.201426 IP hostname.nli.local.38153 > dc.ldap: Flags [.], ack 1578, win 1444, options [nop,nop,TS val 54690399 ecr 19455847], length 0
10:43:14.203080 IP hostname.nli.local.38153 > dc.ldap: Flags [P.], seq 353:586, ack 1578, win 1444, options [nop,nop,TS val 54690399 ecr 19455847], length 233
10:43:14.212292 IP hostname.nli.local.39958 > dc.ldap: Flags [P.], seq 651643402:651643565, ack 654655483, win 2888, options [nop,nop,TS val 55032891 ecr 19374126], length 163
10:43:14.288788 IP hostname.nli.local.38153 > dc.ldap: Flags [.], ack 7117, win 1422, options [nop,nop,TS val 54690420 ecr 19455869], length 0
10:43:14.291937 IP hostname.nli.local.39958 > dc.ldap: Flags [P.], seq 163:353, ack 91, win 2888, options [nop,nop,TS val 55032911 ecr 19455869], length 190
10:43:14.293453 IP hostname.nli.local.39958 > dc.ldap: Flags [.], ack 1578, win 2888, options [nop,nop,TS val 55032912 ecr 19455870], length 0
10:43:14.296267 IP hostname.nli.local.39958 > dc.ldap: Flags [P.], seq 353:586, ack 1578, win 2888, options [nop,nop,TS val 55032912 ecr 19455870], length 233
10:43:14.375968 IP hostname.nli.local.39958 > dc.ldap: Flags [.], ack 7117, win 2844, options [nop,nop,TS val 55032932 ecr 19455890], length 0
10:43:16.737485 IP hostname.nli.local.58569 > dc.ldap: Flags [P.], seq 2429997579:2429997742, ack 112410608, win 1444, options [nop,nop,TS val 54761116 ecr 19378382], length 163
10:43:16.740721 IP hostname.nli.local.58569 > dc.ldap: Flags [P.], seq 163:353, ack 91, win 1444, options [nop,nop,TS val 54761117 ecr 19456481], length 190
10:43:16.742187 IP hostname.nli.local.58569 > dc.ldap: Flags [.], ack 1578, win 1444, options [nop,nop,TS val 54761117 ecr 19456482], length 0
10:43:16.743849 IP hostname.nli.local.58569 > dc.ldap: Flags [P.], seq 353:586, ack 1578, win 1444, options [nop,nop,TS val 54761118 ecr 19456482], length 233
10:43:16.810808 IP hostname.nli.local.58569 > dc.ldap: Flags [.], ack 4474, win 1444, options [nop,nop,TS val 54761135 ecr 19456499], length 0
10:43:16.810914 IP hostname.nli.local.58569 > dc.ldap: Flags [.], ack 7117, win 1444, options [nop,nop,TS val 54761135 ecr 19456499], length 0

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.

Any conclusion on what went wrong here?


  *   Julian

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