[EXT] Re: "key=" on all related log lines

Fri Dec 18 20:03:07 UTC 2020

It's funny that this topic came up today, I just emailed my team on Monday  about some  concerns I have regarding the difference between -k keyname and key=keyname in the audit.rules files.   If I understand this correctly,  some rules assign a keyname with  –k keyname, and other rules use those assigned keynames to filter/limit the scope of the  rule (-F key=keyname).   If this is correct, I believe we may have some rules in the sample 30-stig.rules that would never generate the keyname they are filtering against.   Perhaps this is in error?  For example:

For instance, in the case of system-locale, there are some rules are assigning the keyname  with "-k system-locale” to certain events and other rules filtering what is collected  based on –F key=system-locale, so this one may be ok

	-a always,exit -F arch=b32 -S sethostname,setdomainname -F key=system-locale  
	-a always,exit -F arch=b64 -S sethostname,setdomainname -F key=system-locale  
	-w /etc/issue -p wa -k system-locale  
	-w /etc/issue.net -p wa -k system-locale  
	-w /etc/hosts -p wa -k system-locale 
	-w /etc/hostname -p wa -k system-locale  
	-a always,exit -F dir=/etc/NetworkManager/ -F perm=wa -F key=system-locale 

However, in the case of perm_mod,  there are no rules assigning the keyname with "-k perm_mod", so I suspect that nothing will ever be collected for the rules that are filtering based on perm_mod:

	-a always,exit -F arch=b32 -S chmod,fchmod,fchmodat -F auid>=1000 -F auid!=unset -F key=perm_mod  
	-a always,exit -F arch=b64 -S chmod,fchmod,fchmodat -F auid>=1000 -F auid!=unset -F key=perm_mod 
 	-a always,exit -F arch=b32 -S lchown,fchown,chown,fchownat -F auid>=1000 -F auid!=unset -F key=perm_mod  
	-a always,exit -F arch=b64 -S chown,fchown,lchown,fchownat -F auid>=1000 -F auid!=unset -F key=perm_mod  
	-a always,exit -F arch=b32 -S setxattr,lsetxattr,fsetxattr,removexattr,lremovexattr,fremovexattr -F auid>=1000 -F auid!=unset -F key=perm_mod  
	-a always,exit -F arch=b64 -S setxattr,lsetxattr,fsetxattr,removexattr,lremovexattr,fremovexattr -F auid>=1000 -F auid!=unset -F key=perm_mod

Is this correct?  If so, we may need to make some corrections so related events get assigned the perm_mod keyname , and correct any other similar issues that may exist.  If not, can you explain how events wouold be generated with the  perm_mod keyname?  

Thanks so much,
Karen Wieprecht 

-----Original Message-----
From: linux-audit-bounces at redhat.com <linux-audit-bounces at redhat.com> On Behalf Of Steve Grubb
Sent: Friday, December 18, 2020 8:44 AM
To: Andreas Hasenack <andreas at canonical.com>
Cc: Linux-audit at redhat.com
Subject: [EXT] Re: "key=" on all related log lines

APL external email warning: Verify sender linux-audit-bounces at redhat.com before clicking links or attachments 

On Friday, December 18, 2020 8:24:04 AM EST Andreas Hasenack wrote:
> I use the -k "sometext" parameter in my audit rules, to help analyze 
> the logs. I noticed that it's only added to one of the log lines, not 
> the others, but the tools (ausearch, aureport) find the other related 
> entries nevertheless.

Correct.

> For example:
> 
> -w /etc/shadow -p wa -k shadow-file-changed
> 
> After a "# touch /etc/shadow" I get:
> type=SYSCALL msg=audit(1608297571.005:160): arch=c000003e syscall=257 
> success=yes exit=3 a0=ffffff9c a1=7ffedcecb865 a2=941 a3=1b6 items=2
> ppid=1623 pid=2382 auid=1000 uid=0 gid=0 euid=0 suid=0 fsuid=0 egid=0
> sgid=0 fsgid=0 tty=pts1 ses=1 comm="touch" exe="/bin/touch"
> key="shadow-file-changed"
> type=CWD msg=audit(1608297571.005:160): cwd="/root"
> type=PATH msg=audit(1608297571.005:160): item=0 name="/etc/" inode=206
> dev=fc:01 mode=040755 ouid=0 ogid=0 rdev=00:00 nametype=PARENT
> cap_fp=0000000000000000 cap_fi=0000000000000000 cap_fe=0 cap_fver=0 
> type=PATH msg=audit(1608297571.005:160): item=1 name="/etc/shadow"
> inode=64013 dev=fc:01 mode=0100640 ouid=0 ogid=42 rdev=00:00 
> nametype=NORMAL cap_fp=0000000000000000 cap_fi=0000000000000000
> cap_fe=0 cap_fver=0
> type=PROCTITLE msg=audit(1608297571.005:160):
> proctitle=746F756368002F6574632F736861646F77
> 
> But only the first line has my key.

Correct.

> Are the other entries correlated via the id in "audit(id)"?

They are correlated by the combination of seconds since 1970, millisecond, and serial number. And the records between two events can be interlaced in the logs. Nothing in the klernel serializes the output. So, its entirely on user space to correlate things.

> Is there a way to have the key parameter attached to all of them? 

No.

> I'd like to send to a remote log server only certain events, and if I 
> filter by key, I only get one of these log lines.

Then, I'd say you're not doing it the way it was intended. A simple grep is not sufficient. You would want to use the audit tools or auparse library to do this for you. They take care of the correlation and de-interlacing of events. 
And they can do the filtering. A good example is the setroubleshooter plugin. 
It filters just for AVC's and then sees if they have configuration solutions to avoid the AVC's.

Writing a filre using the auparse library is pretty simple. You can find an example to start from here:

https://github.com/linux-audit/audit-userspace/blob/master/contrib/plugin/
audisp-example.c

I'd also suggest making any plugin double threaded, with one side dequeuing events and the other thread processing them and some kind of queue in between. If the socket buffer between auditd and the plugin gets full, it can affect the audit daemon's performance.

-Steve

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