On 11/9/06, Stephen Smalley <[email protected]> wrote:
Unless I missed something, your plan above would disable SELinux
syslog-related permission checking upon reads of a previously opened
file descriptor to /proc/kmsg. So it would change SELinux behavior in a
way that is directly contrary to the notion of mandatory access control.
Yes, it would do that; no, I don't see why that change is contrary to
the notion of mandatory access control. An open fd on /proc/kmsg
(with my changes applied) offers strictly fewer privileges than
SYSTEM__SYSLOG_MOD (no access to opcodes 4 and 5), and with SELinux
active, you can't get that open fd without having had
SYSTEM__SYSLOG_MOD at some prior time. SELinux does not (as far as I
can tell) do MAC checks for access to normal files at read() time,
only open().
I see this as bringing /proc/kmsg in line with standard Unix file
permission semantics, overall.
Part 4 appears to further expose /proc/kmsg to access by any uid 0
process even if it has no capabilities (think privilege shedding or
containers).
Only in the default privilege model, not in SELinux. (CAP_SYS_ADMIN
is a hell of a lot more powerful than SYSTEM__SYSLOG_MOD.) And I
could be talked out of part 4.
But having a mapping in the core to a much
smaller set of permissions would be even better, and help with
maintenance; the next time someone added a new code, they would more
likely see the mapping table in the core and update it than go digging
into the individual security modules.
But that mapping is itself a security policy decision, and could
plausibly need to be done differently in different security modules...
zw
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