[CentOS] SELinux and access across 'similar types'

Bennett Haselton bennett at peacefire.org
Fri Jan 6 00:37:25 UTC 2012


On 1/5/2012 3:14 PM, RILINDO FOSTER wrote:
> On Jan 5, 2012, at 4:46 PM, Daniel J Walsh wrote:
>
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>> On 01/05/2012 04:36 PM, Bennett Haselton wrote:
>>> http://wiki.centos.org/HowTos/SELinux says: "Access is only allowed
>>> between similar types, so Apache running as httpd_t can read
>>> /var/www/html/index.html of type httpd_sys_content_t."
>>>
>>> however the doc doesn't define what "similar types" means.  I
>>> assumed it just meant "beginning with the same prefix".  However
>>> that can't be right because on my system with SELinux turned on,
>>> httpd runs as type init_t:
>>>
>>> [root at peacefire04 - /root # ps awuxZ | grep httpd | head -n 3
>>> system_u:system_r:init_t:s0     root      2521  0.1  0.4  21680
>>> 8820 ?        Ss   05:05   0:00 /usr/sbin/httpd
>>> system_u:system_r:init_t:s0     apache    2550  0.0  0.4  23364
>>> 8920 ?        S    05:05   0:00 /usr/sbin/httpd
>>> system_u:system_r:init_t:s0     apache    2551  0.1  0.4  22736
>>> 8212 ?        S    05:05   0:00 /usr/sbin/httpd
>>>
>>> and the robots.txt file has type file_t: [root at peacefire04 - /root
>>> # ls -lZ /var/www/html/robots.txt -rw-rw-rw-  root root
>>> system_u:object_r:file_t:s0 /var/www/html/robots.txt
>>>
>>> but Apache can of course access that file.  So in Type Enforcement,
>>> what determines what process type can access what file type?
>>>
>>> Bennett _______________________________________________ CentOS
>>> mailing list CentOS at centos.org
>>> http://lists.centos.org/mailman/listinfo/centos
>>
>> Your machine needs to be relabeled.
>>
>> touch /.autorelabel
>> reboot
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> WARNING: If you have never enabled SELinux for long time, the boot is going to take a while as the system relabels the whole machine. Do not do this unless you can plan for an extend downtime.
>
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I did do
touch /.autorelabel
reboot

The machine booted back up in just a few minutes, what looked like 
normal reboot time.  And then I ran the same commands as before and got 
what looks to me like the same output:

[root at peacefire04 - /root # ls -lZ /var/www/html/robots.txt
-rw-rw-rw-  root root system_u:object_r:file_t:s0      
/var/www/html/robots.txt
[root at peacefire04 - /root # ps awuxZ | grep httpd | head -n 3
system_u:system_r:init_t:s0     root      2530  0.0  0.4  21680  8820 
?        Ss   16:23   0:00 /usr/sbin/httpd
system_u:system_r:init_t:s0     apache    2558  0.8  0.8  28308 16392 
?        S    16:23   0:03 /usr/sbin/httpd
system_u:system_r:init_t:s0     apache    2560  0.5  0.5  23248 10236 
?        S    16:23   0:02 /usr/sbin/httpd

So I'm wondering:
1) How did you know that the machine needed to be relabeled, was it 
something in the output of the commands the first time I ran them? and 
in that case,
2) Why didn't it change after I created /.autorelabel and rebooted?
(I can confirm the file /.autorelabel is no longer present, so it must 
have been deleted when the auto-relabel was done, like the doc says.)
3) If the machine booted back up very quickly, should I be worried that 
the autorelabel might not have happened?  Any idea if it logs a message 
somewhere if it fails to start properly?



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