In the Linux kernel, the following vulnerability has been resolved:
apparmor: fix differential encoding verification
Differential encoding allows loops to be created if it is abused. To prevent this the unpack should verify that a diff-encode chain terminates.
Unfortunately the differential encode verification had two bugs.
- it conflated states that had gone through check and already been
- the order bailout on already checked states compared current chain
Move to a double mark scheme where already verified states get a different mark, than the current chain being kept. This enables us to also drop the backwards verification check that was the cause of the second error as any already verified state is already marked.