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John Johansen a92c5e5086 apparmor: fix race between freeing data and fs accessing it

commit 8e135b8aee upstream.

Backport for conflicts introdued by
- conversion from sha1 to sha256 introduced in
   e44a4dc4b3 ("apparmor: switch SECURITY_APPARMOR_HASH from sha1 to sha256
")

- adding of conditioanl that nests the conflicting code inside an if
  condition
  d61c57fde8 ("apparmor: make export of raw binary profile to userspace optional")

AppArmor was putting the reference to i_private data on its end after
removing the original entry from the file system. However the inode
can and does live beyond that point and it is possible that some of
the fs call back functions will be invoked after the reference has
been put, which results in a race between freeing the data and
accessing it through the fs.

While the rawdata/loaddata is the most likely candidate to fail the
race, as it has the fewest references. If properly crafted it might be
possible to trigger a race for the other types stored in i_private.

Fix this by moving the put of i_private referenced data to the correct
place which is during inode eviction.

Fixes: c961ee5f21 ("apparmor: convert from securityfs to apparmorfs for policy ns files")
Reported-by: Qualys Security Advisory <qsa@qualys.com>
Reviewed-by: Georgia Garcia <georgia.garcia@canonical.com>
Reviewed-by: Maxime Bélair <maxime.belair@canonical.com>
Reviewed-by: Cengiz Can <cengiz.can@canonical.com>
Signed-off-by: John Johansen <john.johansen@canonical.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>