CVE-2024-27014: net/mlx5e: Prevent deadlock while disabling aRFS
In the Linux kernel, the following vulnerability has been resolved:

net/mlx5e: Prevent deadlock while disabling aRFS

When disabling aRFS under the `priv->state_lock`, any scheduled
aRFS works are canceled using the `cancel_work_sync` function,
which waits for the work to end if it has already started.
However, while waiting for the work handler, the handler will
try to acquire the `state_lock` which is already acquired.

The worker acquires the lock to delete the rules if the state
is down, which is not the worker's responsibility since
disabling aRFS deletes the rules.

Add an aRFS state variable, which indicates whether the aRFS is
enabled and prevent adding rules when the aRFS is disabled.

Kernel log:

======================================================
WARNING: possible circular locking dependency detected
6.7.0-rc4_net_next_mlx5_5483eb2 #1 Tainted: G          I
------------------------------------------------------
ethtool/386089 is trying to acquire lock:
ffff88810f21ce68 ((work_completion)(&rule->arfs_work)){+.+.}-{0:0}, at: __flush_work+0x74/0x4e0

but task is already holding lock:
ffff8884a1808cc0 (&priv->state_lock){+.+.}-{3:3}, at: mlx5e_ethtool_set_channels+0x53/0x200 [mlx5_core]

which lock already depends on the new lock.

the existing dependency chain (in reverse order) is:

-> #1 (&priv->state_lock){+.+.}-{3:3}:
       __mutex_lock+0x80/0xc90
       arfs_handle_work+0x4b/0x3b0 [mlx5_core]
       process_one_work+0x1dc/0x4a0
       worker_thread+0x1bf/0x3c0
       kthread+0xd7/0x100
       ret_from_fork+0x2d/0x50
       ret_from_fork_asm+0x11/0x20

-> #0 ((work_completion)(&rule->arfs_work)){+.+.}-{0:0}:
       __lock_acquire+0x17b4/0x2c80
       lock_acquire+0xd0/0x2b0
       __flush_work+0x7a/0x4e0
       __cancel_work_timer+0x131/0x1c0
       arfs_del_rules+0x143/0x1e0 [mlx5_core]
       mlx5e_arfs_disable+0x1b/0x30 [mlx5_core]
       mlx5e_ethtool_set_channels+0xcb/0x200 [mlx5_core]
       ethnl_set_channels+0x28f/0x3b0
       ethnl_default_set_doit+0xec/0x240
       genl_family_rcv_msg_doit+0xd0/0x120
       genl_rcv_msg+0x188/0x2c0
       netlink_rcv_skb+0x54/0x100
       genl_rcv+0x24/0x40
       netlink_unicast+0x1a1/0x270
       netlink_sendmsg+0x214/0x460
       __sock_sendmsg+0x38/0x60
       __sys_sendto+0x113/0x170
       __x64_sys_sendto+0x20/0x30
       do_syscall_64+0x40/0xe0
       entry_SYSCALL_64_after_hwframe+0x46/0x4e

other info that might help us debug this:

 Possible unsafe locking scenario:

       CPU0                    CPU1
       ----                    ----
  lock(&priv->state_lock);
                               lock((work_completion)(&rule->arfs_work));
                               lock(&priv->state_lock);
  lock((work_completion)(&rule->arfs_work));

 *** DEADLOCK ***

3 locks held by ethtool/386089:
 #0: ffffffff82ea7210 (cb_lock){++++}-{3:3}, at: genl_rcv+0x15/0x40
 #1: ffffffff82e94c88 (rtnl_mutex){+.+.}-{3:3}, at: ethnl_default_set_doit+0xd3/0x240
 #2: ffff8884a1808cc0 (&priv->state_lock){+.+.}-{3:3}, at: mlx5e_ethtool_set_channels+0x53/0x200 [mlx5_core]

stack backtrace:
CPU: 15 PID: 386089 Comm: ethtool Tainted: G          I        6.7.0-rc4_net_next_mlx5_5483eb2 #1
Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS rel-1.13.0-0-gf21b5a4aeb02-prebuilt.qemu.org 04/01/2014
Call Trace:
 <TASK>
 dump_stack_lvl+0x60/0xa0
 check_noncircular+0x144/0x160
 __lock_acquire+0x17b4/0x2c80
 lock_acquire+0xd0/0x2b0
 ? __flush_work+0x74/0x4e0
 ? save_trace+0x3e/0x360
 ? __flush_work+0x74/0x4e0
 __flush_work+0x7a/0x4e0
 ? __flush_work+0x74/0x4e0
 ? __lock_acquire+0xa78/0x2c80
 ? lock_acquire+0xd0/0x2b0
 ? mark_held_locks+0x49/0x70
 __cancel_work_timer+0x131/0x1c0
 ? mark_held_locks+0x49/0x70
 arfs_del_rules+0x143/0x1e0 [mlx5_core]
 mlx5e_arfs_disable+0x1b/0x30 [mlx5_core]
 mlx5e_ethtool_set_channels+0xcb/0x200 [mlx5_core]
 ethnl_set_channels+0x28f/0x3b0
 ethnl_default_set_doit+0xec/0x240
 genl_family_rcv_msg_doit+0xd0/0x120
 genl_rcv_msg+0x188/0x2c0
 ? ethn
---truncated---
CVSS v3.1: 5.5