10:19 p.m.
Hi all,
I'm developing custom audit client to monitor Linux system activities.
I'm testing my client from Ubuntu 14.04 (64-bit) system with the following auditctl
rules.
sudo auditctl -l
LIST_RULES: exit,always arch=3221225534 (0xc000003e)
syscall=open,close,dup,dup2,socket,connect,accept,listen,socketpair,clone,fork,vfork,execve,exit,creat,unlink,exit_group,openat,unlinkat,accept4,dup3
And I captured the raw system messages with the following command.
sudo auditd -f > /tmp/log.txt
While /tmp/log.txt contains a considerable amount of raw audit messages, I grep'ed
only connect() system calls with its associated saddr entries.
grep -A1 -e "syscall=42 success=yes" /tmp/log.txt
--
type=SYSCALL msg=audit(1459302277.538:35891018): arch=c000003e syscall=42 success=yes
exit=0 a0=61 a1=7f2ec75a1ed0 a2=10 a3=1 items=0 ppid=2779 pid=21581 auid=4294967295
uid=8271 gid=5001 euid=8271 suid=8271 fsuid=8271 egid=5001 sgid=5001 fsgid=5001 tty=(none)
ses=4294967295 comm="Chrome_IOThread" exe="/opt/google/chrome/chrome"
key=(null)
type=SOCKADDR msg=audit(1459302277.538:35891018): saddr=020000358A0F6C0B0000000000000000
--
type=SYSCALL msg=audit(1459302309.098:35898719): arch=c000003e syscall=42 success=yes
exit=0 a0=6 a1=7fffe9a24980 a2=10 a3=7fffe9a246d0 items=0 ppid=20312 pid=2991
auid=4294967295 uid=8271 gid=5001 euid=0 suid=0 fsuid=0 egid=0 sgid=5001 fsgid=0 tty=pts23
ses=4294967295 comm="sudo" exe="/usr/bin/sudo" key=(null)
type=SOCKADDR msg=audit(1459302309.098:35898719): saddr=0200006F8A0FA5090000000000000000
--
type=SYSCALL msg=audit(1459302309.098:35898722): arch=c000003e syscall=42 success=yes
exit=0 a0=6 a1=7fffe9a24980 a2=10 a3=7fffe9a246d0 items=0 ppid=20312 pid=2991
auid=4294967295 uid=8271 gid=5001 euid=0 suid=0 fsuid=0 egid=0 sgid=5001 fsgid=0 tty=pts23
ses=4294967295 comm="sudo" exe="/usr/bin/sudo" key=(null)
type=SOCKADDR msg=audit(1459302309.098:35898722): saddr=0200030B8A0FA5090000000000000000
...
For these entries, I decoded saddr entries with the attached program and extracted entries
port values '0'.
g++ -o sock_decode sock_decode.cpp
grep -A1 -e "syscall=42 success=yes" /tmp/log.txt |grep saddr | awk
'BEGIN{FS="="} {print “ ./sock_decode " $4}' |sh |grep
"sa_family: 2.* port: 0" |more
0200000036447A640000000000000000: sa_family: 2 addr: 1685734454, port: 0 (0)
020000003644ECD00000000000000000: sa_family: 2 addr: 3505144886, port: 0 (0)
02000000369520250000000000000000: sa_family: 2 addr: 622892342, port: 0 (0)
....
If I understood correctly, connect() should return error when sin_port field is set with
'0'.
Would anyone explain this to me or help me with fix this problem?
Thanks a lot for your help in advance!
6:33 a.m.
Dear Steve,
Thanks a lot for your quick response.
Would you tell me from what saddr fields that you get the port number value ‘779’?
This might indicate my code to extract the field might be wrong. Would you also inform me
what is the correct way to decode saddr string?
Thanks again!
Regards, Kangkook
7:54 a.m.
I checked out with strings that I provided from the previous email.
The first 3 ones gave me proper port numbers.
$ ~/bin/sock_decode 020000358A0F6C0B0000000000000000
020000358A0F6C0B0000000000000000: sa_family: 2 addr: 191631242, port: 53 (13568)
$ ~/bin/sock_decode 0200006F8A0FA5090000000000000000
0200006F8A0FA5090000000000000000: sa_family: 2 addr: 161812362, port: 111 (28416)
$ ~/bin/sock_decode 0200030B8A0FA5090000000000000000
0200030B8A0FA5090000000000000000: sa_family: 2 addr: 161812362, port: 779 (2819)
but, last three one didn’t
$ ~/bin/sock_decode 0200000036447A640000000000000000
0200000036447A640000000000000000: sa_family: 2 addr: 1685734454, port: 0 (0)
$ ~/bin/sock_decode 020000003644ECD00000000000000000
020000003644ECD00000000000000000: sa_family: 2 addr: 3505144886, port: 0 (0)
$ ~/bin/sock_decode 02000000369520250000000000000000
02000000369520250000000000000000: sa_family: 2 addr: 622892342, port: 0 (0)
Would you check this out?
/Kangkook
4:50 p.m.
On Thursday, March 31, 2016 08:54:30 AM Kangkook Jee wrote:
You didn't give the events, but rather the sockaddr field alone. Port 0 is
valid in some uses. It mean give me an ephemeral port.
http://lxr.free-electrons.com/source/net/ipv4/inet_connection_sock.c#L90
90 /* Obtain a reference to a local port for the given sock,
91 * if snum is zero it means select any available local port.
-Steve
5:11 p.m.
Here an event directly from auditd for connect() system call (syscall=42) with port number
0.
Do you think connect() system call still can be called with port number 0?
type=SYSCALL msg=audit(1459301607.178:35720095): arch=c000003e syscall=42 success=yes
exit=0 a0=2c a1=7f1fbe8f81f0 a2=10 a3=0 items=0 ppid=2779 pid=31713 auid=4294967295
uid=8271 gid=5001 euid=8271 suid=8271 fsuid=8271 egid=5001 sgid=500#
type=SOCKADDR msg=audit(1459301607.178:35720095): saddr=0200000036447A640000000000000000
If it is bind() it makes but I’m not sure we can still do this with connect().
Thanks!
/Kangkook
type=SYSCALL msg=audit(1459301607.178:35720095): arch=c000003e syscall=42 success=yes
exit=0 a0=2c a1=7f1fbe8f81f0 a2=10 a3=0 items=0 ppid=2779 pid=31713 auid=4294967295
uid=8271 gid=5001 euid=8271 suid=8271 fsuid=8271 egid=5001 sgid=500#
type=SOCKADDR msg=audit(1459301607.178:35720095): saddr=0200000036447A640000000000000000
7:13 a.m.
On Thursday, March 31, 2016 06:11:26 PM Kangkook Jee wrote:
Hello,
I got the full events. Below is the explanation...
type=SYSCALL msg=audit(03/29/2016 21:33:27.178:35720094) : arch=x86_64
syscall=socket success=yes exit=44 a0=inet a1=SOCK_DGRAM a2=ip a3=0x0 items=0
ppid=2779 pid=31713 auid=unset uid=unknown(8271) gid=unknown(5001)
euid=unknown(8271) suid=unknown(8271) fsuid=unknown(8271) egid=unknown(5001)
sgid=unknown(5001) fsgid=unknown(5001) tty=(none) ses=unset comm=DNS Res~er
#465 exe=/usr/lib/firefox/firefox key=(null)
So, here ^^^ we are creating a DGRAM socket. This is important because they
follow slightly different rules than tcp.
type=SOCKADDR msg=audit(03/29/2016 21:33:27.178:35720095) : saddr=inet
host:54.68.122.100 serv:0
type=SYSCALL msg=audit(03/29/2016 21:33:27.178:35720095) : arch=x86_64
syscall=connect success=yes exit=0 a0=0x2c a1=0x7f1fbe8f81f0 a2=0x10 a3=0x0
items=0 ppid=2779 pid=31713 auid=unset uid=unknown(8271) gid=unknown(5001)
euid=unknown(8271) suid=unknown(8271) fsuid=unknown(8271) egid=unknown(5001)
sgid=unknown(5001) fsgid=unknown(5001) tty=(none) ses=unset comm=DNS Res~er
#465 exe=/usr/lib/firefox/firefox key=(null)
http://man7.org/linux/man-pages/man2/connect.2.html
If the socket sockfd is of type SOCK_DGRAM, then addr is the address to which
datagrams are sent by default, and the only address from which datagrams are
received.
So, this is just setting up a connectionless socket to a specific server.
Judging by the thread name, this is for DNS resolution for Firefox. So, I
would say that without a doubt, this is normal system operation.
-Steve
3427
days inactive
3432
days old
linux-audit@lists.linux-audit.osci.io
7 comments
2 participants
participants (2)
-
Kangkook Jee -
Steve Grubb