net/mlx5: Fix deadlock between devlink lock and esw->wq

Overview

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

net/mlx5: Fix deadlock between devlink lock and esw->wq

esw->work_queue executes esw_functions_changed_event_handler -> esw_vfs_changed_event_handler and acquires the devlink lock.

.eswitch_mode_set (acquires devlink lock in devlink_nl_pre_doit) -> mlx5_devlink_eswitch_mode_set -> mlx5_eswitch_disable_locked -> mlx5_eswitch_event_handler_unregister -> flush_workqueue deadlocks when esw_vfs_changed_event_handler executes.

Fix that by no longer flushing the work to avoid the deadlock, and using a generation counter to keep track of work relevance. This avoids an old handler manipulating an esw that has undergone one or more mode changes:

• the counter is incremented in mlx5_eswitch_event_handler_unregister.
• the counter is read and passed to the ephemeral mlx5_host_work struct.
• the work handler takes the devlink lock and bails out if the current generation is different than the one it was scheduled to operate on.
• mlx5_eswitch_cleanup does the final draining before destroying the wq.

No longer flushing the workqueue has the side effect of maybe no longer cancelling pending vport_change_handler work items, but that's ok since those are disabled elsewhere:

• mlx5_eswitch_disable_locked disables the vport eq notifier.
• mlx5_esw_vport_disable disarms the HW EQ notification and marks vport->enabled under state_lock to false to prevent pending vport handler from doing anything.
• mlx5_eswitch_cleanup destroys the workqueue and makes sure all events are disabled/finished.

Affected

• Linux >= f1bc646c9a06f09aad5d8bacb87103b5573ee45e < 0de867f6e34eae6907b367fd152c55e61cb98608
• Linux >= f1bc646c9a06f09aad5d8bacb87103b5573ee45e < 957d2a58f7f8ebcbdd0a85935e0d2675134b890d
• Linux >= f1bc646c9a06f09aad5d8bacb87103b5573ee45e < 3c7313cb41b1b427078440364d2f042c276a1c0b
• Linux >= f1bc646c9a06f09aad5d8bacb87103b5573ee45e < 4a7838bebc38374f74baaf88bf2cf8d439a92923
• Linux >= f1bc646c9a06f09aad5d8bacb87103b5573ee45e < 90e7e5d14d0bd25ffd019a3aa39d9f1c05fedbe1
• Linux >= f1bc646c9a06f09aad5d8bacb87103b5573ee45e < aed763abf0e905b4b8d747d1ba9e172961572f57
• Linux 6.0

Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.