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Currently mediates_X stub rules are added to the dfa to ensure a valid
transition state will exist if X should be mediated. The kernel uses
this to test whether the dfa supports certain mediation classes.
Unfortunately the mediates stub rules can be removed by other rules,
combined with minimization. In the allow case this is not a problem,
as if the stub rule is removed it will be due to state merging and the
test will still be valid. Unfortunately the deny case can wipe out the
stub rule in a couple of cases, meaning the when the kernel tests that
its in a valid state for mediation it will fail and treat the dfa as
not mediating the rule type, which results in allowing instead of
denying.
Fix this by making sure mediated stub rules can't be overridden by a
deny rule by giving them maximum priority.
Note: there is another issue with stub rule elimination in the allow
case. It will can cause equality tests to fail when combined
with priority rules, because the stub rules where added at
priority 0 and an actual rule of higher priority could
completely override it removing the permission on the stub rule.
This issue will be caught by the equality.sh tests in the
following patch that exposes priority to rules in policy.
Signed-off-by: John Johansen <john.johansen@canonical.com>
The apparmor_parser allows you to add, replace, and remove AppArmor policy through the use of command line options. The default is to add. `apparmor_parser --help` shows what the command line options are. You can also find more information at https://wiki.apparmor.net -- The AppArmor development team