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SubjectIP DoS on 2.2.17
Please excuse a post from a non-member, but this seems the
most suitable place I could find. Please e-mail me any
thoughts, and I'll summarise if I make any progress.

I am getting some sort of IP DoS (Side effect of a Port
scan), and am trying to unpick the cause (Other than nasty
hackers).

The symptom is that after a specific type of scan (ipchain
logs below), and 4 packets logged on port 111, the machine
loses the ability to send "outgoing" packets (both UDP and
TCP). PLOAD shows a dimishing dribble of incoming packets,
presumably the remains of the scan, plus the odd attempt to
send me something useful.

The only way to reset this (short of a reboot) is to take
down the PPP interface, by killing ppp watch (NB "ifdown
ppp0" results in ppp-watch restarting the Interface, but the
ISDN never connects successfully?!?), ifdown ppp0, rmmod -a
(Takes out down to and including slhc in list below, I
haven't yet tried stepping through the modules to see which
one is confused).


What is best way to proceed - assuming I want to understand
what is happening rather than just lock everything down (I'd
prefer to do both of course)?

Should I upgrade to 2.2.19 and hope it goes away (I'll
probably do this anyway, but reading release notes I'm not
immediately struck by anything obvious)?

Any one any idea on the scanner in use? If I could reproduce
the problem at will I'd be in a better position to analyse
what is happening.

I don't understand why I am the only one seeing this (I
found some promising references, only to find they were many
kernel revisions out of date) - it is a very infrequent
problem (Despite seeing scans against port 111 every few
hours, I've only seen this problem a handful of times).

Maybe others just assume it is yet another ISP problem and
reboot?!, but the ability to only get incoming packets is
rather distinctive (Although I only spotted this as I
happened to have pload running).

As a temporary supplement to security I've stuck in
"iptrap", with a custom script, which mails me, and then
kills all traffic between my box, and anyone creating
unauthorised TCP connections to well known services
(Including 111), but this hasn't cured the issue (So maybe
it isn't the port 111 part of the scan!?), although I
blacklisted three wannabe hackers last night.

Jul 7 18:48:26 linux1 kernel: Packet log: input DENY ppp0
PROTO=6 211.250.197.2:3024 193.237.109.203:111 L=60 S=0x00
I=14018 F=0x4000 T=43 SYN (#3)
Jul 7 18:48:26 linux1 kernel: Packet log: input DENY ppp0
PROTO=6 211.250.197.2:3024 193.237.109.203:111 L=60 S=0x00
I=14018 F=0x4000 T=43 SYN (#3)
Jul 7 18:48:29 linux1 kernel: Packet log: input DENY ppp0
PROTO=6 211.250.197.2:3024 193.237.109.203:111 L=60 S=0x00
I=15081 F=0x4000 T=43 SYN (#3)
Jul 7 18:48:29 linux1 kernel: Packet log: input DENY ppp0
PROTO=6 211.250.197.2:3024 193.237.109.203:111 L=60 S=0x00
I=15081 F=0x4000 T=43 SYN (#3)

Portmapper isn't running, nor any of the known "problem"
Redhat services, inetd.conf has one line "imap", Postfix
supplies SMTP (Which is usually good at logging odd
activity), and ipchains filters the other services which
refuse to be bound to Internal interfaces only. TCP wrappers
is also in there somewhere telling some wrapper aware
programs who to trust.

Masquerading is enabled, but no masqueraded machines are
powered on overnight when this seems to occur most often.

Linux box, based on Redhat 6.1, later upgraded to 7.0.
It runs Kernel 2.2.17, ipchains 1.3.9, ppp-2.3.11-7, BT
Speedway ISDN card (Hence hisax driver).

lsmod
Module Size Used by
ppp_deflate 40852 0 (autoclean)
bsd_comp 3884 0 (autoclean)
hisax 143816 1 (autoclean)
isdn 111596 1 (autoclean) [hisax]
ppp 20140 2 (autoclean) [ppp_deflate
bsd_comp]
slhc 4440 1 (autoclean) [isdn ppp]
rtl8139 12416 1 (autoclean)
wvlan_cs 23616 1
ds 6280 2 [wvlan_cs]
i82365 21984 2
pcmcia_core 44512 0 [wvlan_cs ds i82365]
cmpci 22124 0
soundcore 2372 4 [cmpci]

As yet no evidence of any successful intrusion, but I'm
trying to run some interesting software for which a really
solid Internet connection would be useful.

Simon
--
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