UPSTREAM: net/sched: sch_hfsc: Ensure inner classes have fsc curve

[ Upstream commit b3d26c57 ]

HFSC assumes that inner classes have an fsc curve, but it is currently
possible for classes without an fsc curve to become parents. This leads
to bugs including a use-after-free.

Don't allow non-root classes without HFSC_FSC to become parents.

Bug: 300027510
Fixes: 1da177e4 ("Linux-2.6.12-rc2")
Reported-by: Budimir Markovic <markovicbudimir@gmail.com>
Signed-off-by: Budimir Markovic <markovicbudimir@gmail.com>
Acked-by: Jamal Hadi Salim <jhs@mojatatu.com>
Link: https://lore.kernel.org/r/20230824084905.422-1-markovicbudimir@gmail.com


Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
(cherry picked from commit a1e820fc)
Signed-off-by: Lee Jones <joneslee@google.com>
Change-Id: I7d839127f7e1709cb571ac22a19aec08e6deec18