On 04/08/14 17:47, Stephen Smalley wrote:
On 04/08/2014 08:16 AM, Stephen Smalley wrote:
On 04/08/2014 04:40 AM, dE wrote:
As I read in the SELinux docs, each subject and object is assigned a
unique SID; when using the selinux libraries, or using the SELinux
kernel API the programs are expected to request the security server
decisions for a particular subject and object by passing the subject and
object's SID to the security server.
Question is -- is SID created when an SELinux enabled kernel boots or
just when a SELinux enabled program requests an SID for a subject/object
from the kernel?
Also can I see a process's and file's SID via some program?
Except for a small set of predefined initial SIDs (used for
bootstrapping before policy is loaded), SIDs are dynamically allocated
on demand for security contexts when they are first used.
The kernel does not expose its SIDs to userspace; all of the userspace
APIs provided by the kernel pass security contexts instead; see:
http://www.nsa.gov/research/_files/selinux/papers/module/x362.shtml
However, libselinux does provide a userspace SID abstraction for users
of the userspace AVC implementation (man avc_context_to_sid). Those
SIDs are likewise dynamically allocated on demand for security contexts
when they are first used, but are merely local references to the
security context; that mapping is per-process and has no global meaning.
Also, SIDs are not unique per subject/object but rather per security
context.
It doesn't make sense to give each subject and object unique SID cause
the security server doesn't have to do anything with individual subject
and object instead it has to do with the security context.
That clears things up. Thanks!
