SE Linux lacks proper user notification for security violations

Steve G linux_4ever at
Sat Jun 25 12:48:21 UTC 2005


>This highlights a serious concern of mine: Lots of time is being wasted
>tracking down strange problems because the only place SE Linux has to
>report security errors is in dmesg and the system log.

The avc denial goes to the kernel audit system. It in turn decides whether to
send it to the audit daemon or syslog. The audit daemon is the preferred
disposition for avc messages.

>When the cgi program would not produce any output at all it was not 
>even obvious that it was a security problem.

This problem is really caused by the fact that cgi programs should not output
errors or you will draw the attention of hackers. The rule of the road is that
each program is responsible for reporting its own errors.

>Traditionally when there is a security policy violation you get a
>"permission denied" on the tty.

And guess who is responsible for writing that message? Its not the kernel.

>We have got to find a way to make an error appear on the tty associated 
>with the process that caused the violation. I think I am going to look 
>into setting up syslog to log all such security messages to all tty's 
>until I can find a better solution.

A better solution is to check the return code of any OS related syscall and write
the error to a log. This is what I do when I write cgi-bin apps. You can't write
them to stdout or you are asking to be hacked.

>But what is the better solution? I suspect that now that we have a very
>granular way of specifying security policy we will need a more granular
>way to report errors back to the user.

tail -f /var/log/audit/audit.log

will show you something in realtime. The audit daemon will be getting some event
dispatcher code over the next month or two. This will help out as you could have
a client app that write it to the console for you.

>I am having a rather difficult time selling SE Linux in my business due
>to issues like this. People really hate it when this cool new security
>feature causes things to fail in dark and mysterious ways. I have been
>forced to disable it on all of our machines lest we have a developer

Your problem is not really SE Linux, its that every syscall needs to have its
return code checked. Your applications need to handle errors in a way that you
can do post-mortum analysis. If it reports permission denied, you should take a
look at file permissions and review audit events. It really is that simple.

I think you can use dmesg -n xx to make syslog messages appear on the console,
too. Maybe that will help in the interim?

Hope this helps...

-Steve Grubb

Do you Yahoo!? 
Read only the mail you want - Yahoo! Mail SpamGuard. 

More information about the fedora-selinux-list mailing list