net: switchdev: Convert blocking notification chain to a raw one

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

net: switchdev: Convert blocking notification chain to a raw one

A blocking notification chain uses a read-write semaphore to protect the

integrity of the chain. The semaphore is acquired for writing when

adding / removing notifiers to / from the chain and acquired for reading

when traversing the chain and informing notifiers about an event.

In case of the blocking switchdev notification chain, recursive

notifications are possible which leads to the semaphore being acquired

twice for reading and to lockdep warnings being generated [1].

Specifically, this can happen when the bridge driver processes a

SWITCHDEV_BRPORT_UNOFFLOADED event which causes it to emit notifications

about deferred events when calling switchdev_deferred_process().

Fix this by converting the notification chain to a raw notification

chain in a similar fashion to the netdev notification chain. Protect

the chain using the RTNL mutex by acquiring it when modifying the chain.

Events are always informed under the RTNL mutex, but add an assertion in

call_switchdev_blocking_notifiers() to make sure this is not violated in

the future.

Maintain the "blocking" prefix as events are always emitted from process

context and listeners are allowed to block.

[1]:

WARNING: possible recursive locking detected

6.14.0-rc4-custom-g079270089484 #1 Not tainted

--------------------------------------------

ip/52731 is trying to acquire lock:

ffffffff850918d8 ((switchdev_blocking_notif_chain).rwsem){++++}-{4:4}, at: blocking_notifier_call_chain+0x58/0xa0

but task is already holding lock:

ffffffff850918d8 ((switchdev_blocking_notif_chain).rwsem){++++}-{4:4}, at: blocking_notifier_call_chain+0x58/0xa0

other info that might help us debug this:

Possible unsafe locking scenario:

CPU0

----

lock((switchdev_blocking_notif_chain).rwsem);

lock((switchdev_blocking_notif_chain).rwsem);

*** DEADLOCK ***

May be due to missing lock nesting notation

3 locks held by ip/52731:

#0: ffffffff84f795b0 (rtnl_mutex){+.+.}-{4:4}, at: rtnl_newlink+0x727/0x1dc0

#1: ffffffff8731f628 (&net->rtnl_mutex){+.+.}-{4:4}, at: rtnl_newlink+0x790/0x1dc0

#2: ffffffff850918d8 ((switchdev_blocking_notif_chain).rwsem){++++}-{4:4}, at: blocking_notifier_call_chain+0x58/0xa0

stack backtrace:

...

? __pfx_down_read+0x10/0x10

? __pfx_mark_lock+0x10/0x10

? __pfx_switchdev_port_attr_set_deferred+0x10/0x10

blocking_notifier_call_chain+0x58/0xa0

switchdev_port_attr_notify.constprop.0+0xb3/0x1b0

? __pfx_switchdev_port_attr_notify.constprop.0+0x10/0x10

? mark_held_locks+0x94/0xe0

? switchdev_deferred_process+0x11a/0x340

switchdev_port_attr_set_deferred+0x27/0xd0

switchdev_deferred_process+0x164/0x340

br_switchdev_port_unoffload+0xc8/0x100 [bridge]

br_switchdev_blocking_event+0x29f/0x580 [bridge]

notifier_call_chain+0xa2/0x440

blocking_notifier_call_chain+0x6e/0xa0

switchdev_bridge_port_unoffload+0xde/0x1a0

...