No default labels, is it intentional?

Tue Jan 15 15:10:45 UTC 2013

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On 01/15/2013 10:03 AM, Dominick Grift wrote:
> On Tue, 2013-01-15 at 09:58 -0500, Daniel J Walsh wrote:
>> On 01/15/2013 09:15 AM, Dominick Grift wrote:
>>> On Tue, 2013-01-15 at 14:11 +0100, Göran Uddeborg wrote:
>>>> I'm running a "restorecon -n -R -v /" from cron once a month, just to
>>>> be careful and know what is happening.  Last night when it ran, I got
>>>> a lot of error messages like these:
>>>> 
>>>> restorecon:  Warning no default label for /dev/pts/3
>>>> 
>>>> and
>>>> 
>>>> restorecon:  Warning no default label for /tmp/efs0YYVa79.html
>>>> 
>>>> There were a couple for things in /dev, and lots of them for things
>>>> in /tmp.
>>>> 
>>>> I have lately been upgrading bit by bit to Fedora 18 (the beta,
>>>> strictly speaking, since the final release isn't officially out at
>>>> the time of this writing), so I assume the new message is related to
>>>> these upgrades. But why?  When I list file contexts, I see rules like
>>>> this:
>>>> 
>>>> /dev/pts(/.*)?                                     all files 
>>>> <<None>>
>>>> 
>>>> So I guess it is not a simple mistake.  But what is the reason?  Why
>>>>  don't some /dev entries, and almost the entire /tmp directory, have
>>>> any default context any more?
>>> 
>>> It has to do with some optional security models like mcs, mls and ubac
>>> and the nature of their security attributes i believe
>>> 
>>> For example if you create a file in /tmp with a compartment of s0:c23
>>> then you do not want a relabel to reset it because that would
>>> declassify the file back to s0
>>> 
>>> SELinux cannot determine that the file should be labeled s0:c23 because
>>> a unprivileged user with access to the compartment decided that
>>> 
>>> So by ignoring the context altogether you can be sure that the file
>>> will not get declassified by restorecon/fixfiles
>>> 
>>> So you will see this in public places like /tmp etc.
>>> 
>>> There is a similar issue with types. Users may have some discretion
>>> over select types to relabel to and from. SELinux cannot determine that
>>> a user decided to label from example file ~/bla type
>>> httpd_user_content_t.
>>> 
>>> So with types there is a different approach: some types are declared 
>>> customizable types. If a file has a customizable type then SELinux will
>>> not try to relabel it (so that it wont get unintentionally
>>> declassified) unless you use the -F flag.
>>> 
>>> The identity field by default does not get reset unless one uses
>>> restorecon with the -F flag
>>> 
>>> With MLS security models processes are forced to operate on specified 
>>> security levels for the sake of enforcing confidentiality. Files that
>>> may be affected and are in public places are not flagged to be reset
>>> with the <<None>>
>>> 
>>> Disclaimer: this is my understanding of the issue but i might be wrong
>>> 
>>> 
>>> 
>>>> -- selinux mailing list selinux at lists.fedoraproject.org 
>>>> https://admin.fedoraproject.org/mailman/listinfo/selinux
>>> 
>>> 
>>> -- selinux mailing list selinux at lists.fedoraproject.org 
>>> https://admin.fedoraproject.org/mailman/listinfo/selinux
>>> 
>> Yes the basic idea is in certain directories like mnt_t, tmp_t, tmpfs_t
>> we do not have a standard definition of content in these directories.  So
>> <<none>> says any content could be here, so don't change the labels.  For
>> example a user does cp -a ~/.ssh /tmp  Would move ssh_home_t content to
>> /tmp, if you ran restorecon on it and we had default label of tmp_t or
>> user_tmp_t, then all apps could read tmp_t could not read the content.
>> 
>> Modern restorecon in RHEL7 and Latest Fedoras does not change any
>> components of the security context other then the type field.  unless you
>> specify force. This is something we want avoid as we move forward with
>> MCS labeling and MLS Labeling.  If you use containers or static labeling
>> for virtual machines, you do not want restorecon changing the MLS/MCS
>> field.
>> 
>> The reason you are noticing this is we added an error check to restorecon
>> to tell the user that restorecon /mnt/foobar did not do anything.
>> 
>> restorecon -R /mnt
>> 
>> Will not output the error, since we wanted to quiet the noise, but if you
>> get verbose, you will get the noise.  I guess we could add a -vv for
>> realy verbose, if the message is aggravating.
> 
> By the way, we probably want to not relabel content in
> /var/lib/libvirt/filesystems.
> 
> I did a relabel and all my container contexts were reset
> 
Really, I don't see that

# restorecon -R -v /var/lib/libvirt/filesystems/
# ls -lZ /var/lib/libvirt/filesystems/
drwxr-xr-x. root root system_u:object_r:svirt_lxc_file_t:s0:c1,c2 apache1
drwxr-xr-x. root root system_u:object_r:svirt_lxc_file_t:s0:c1,c2 container1
drwxr-xr-x. root root system_u:object_r:svirt_lxc_file_t:s0:c0.c1023 dan
drwxr-xr-x. root root system_u:object_r:svirt_lxc_file_t:s0:c0.c1023 myapache
drwxr-xr-x. root root system_u:object_r:svirt_lxc_file_t:s0:c0.c1023 mymysql

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