tree a4c5c40884a7bcb9cdf12d6e7184fe19699b1894
parent 7178784f0a94e2e6c668f587665fde41d405a23c
author Dmitry Kasatkin <d.kasatkin@samsung.com> 1412336421 +0300
committer Mimi Zohar <zohar@linux.vnet.ibm.com> 1413084782 -0400

ima: use atomic bit operations to protect policy update interface

The current implementation uses an atomic counter to provide exclusive
access to the sysfs 'policy' entry to update the IMA policy. While it is
highly unlikely, the usage of a counter might potentially allow another
process to overflow the counter, open the interface and insert additional
rules into the policy being loaded.

This patch replaces using an atomic counter with atomic bit operations
which is more reliable and a widely used method to provide exclusive access.

As bit operation keep the interface locked after successful update, it makes
it unnecessary to verify if the default policy was set or not during parsing
and interface closing. This patch also removes that code.

Changes in v3:
* move audit log message to ima_relead_policy() to report successful and
  unsuccessful result
* unnecessary comment removed

Changes in v2:
* keep interface locked after successful policy load as in original design
* remove sysfs entry as in original design

Signed-off-by: Dmitry Kasatkin <d.kasatkin@samsung.com>
Signed-off-by: Mimi Zohar <zohar@linux.vnet.ibm.com>