apparmor: fix race on rawdata dereference

In the Linux kernel, the following vulnerability has been resolved:

apparmor: fix race on rawdata dereference

There is a race condition that leads to a use-after-free situation:

because the rawdata inodes are not refcounted, an attacker can start

open()ing one of the rawdata files, and at the same time remove the

last reference to this rawdata (by removing the corresponding profile,

for example), which frees its struct aa_loaddata; as a result, when

seq_rawdata_open() is reached, i_private is a dangling pointer and

freed memory is accessed.

The rawdata inodes weren't refcounted to avoid a circular refcount and

were supposed to be held by the profile rawdata reference. However

during profile removal there is a window where the vfs and profile

destruction race, resulting in the use after free.

Fix this by moving to a double refcount scheme. Where the profile

refcount on rawdata is used to break the circular dependency. Allowing

for freeing of the rawdata once all inode references to the rawdata

are put.