Re: Runtime flexibility of SELInux

Tim Sheppard <tsheppard@xxxxxxxxxxxxxxx> · Wed, 25 Apr 2012 10:37:07 +0100

On 24/04/12 18:37, Daniel J Walsh wrote:

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On 04/24/2012 01:16 PM, Tim Sheppard wrote:

Hi,

I am looking to use SELinux to secure a process that is made up of a number
of discrete, sequential stages. One stage communicates to the next by
writing results to a file and then an external process modifies the SELinux
context of the file to allow the next stage to read the file and so on
until the final stage is reached and the processing stops.

The problem I have is that the number of stages is variable and can change
with each invocation of the process, i.e. when I create the process I know
the number of stages that will be required in it, but the number of stages
could change with each invocation. I think therefore, that I need a means
of creating new contexts on the fly and assigning them to the processes. Is
it possible with SELinux to create a new security context (domain for the
output file, and user/role for the stage process) on the fly and execute a
process within that context such that it could poll a directory for input
files and, if it is permitted to read the file perform its operation?

Many Thanks,

Tim Sheppard

If each process is going to require the same approximate access. I would use
MCS labeling for separation.

Basically define a sandbox type for your processes to run within and then have
your controlling app pick an MCS label for the process and the content.

chcon -t confined_file_t -l s0:c1 passing.file
runcon -t confined_proc_t -l s0:c1 proc1
When done
chcon -l s0:c2 passing.file
runcon -t confined_proc_t -l s0:c2 proc2
...
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The other thing I need to be able to do is constrain a process to only 

permit it to change a context from c1 -> c2 (or label1 -> label2 in the 

general case). Is this possible to manage in a policy at all and if so 

is there any runtime flexibility over the rules that can be created to 

allow me to specify the only legal changes are c1 -> c2 -> c3 -> end for 

process1-1 and c1 -> c2 -> c3 -> c4-> c5 -> end for process1-2. 

Essentially, I need to be able to ensure that a process cannot change 

the security labelling to bypass a stage in the chain.

Many Thanks,

Tim

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