wifi: mt76: mt7921e: fix use-after-free in free_irq()

From commit a304e1b ("[PATCH] Debug shared irqs"), there is a test
to make sure the shared irq handler should be able to handle the unexpected
event after deregistration. For this case, let's apply MT76_REMOVED flag to
indicate the device was removed and do not run into the resource access
anymore.

BUG: KASAN: use-after-free in mt7921_irq_handler+0xd8/0x100 [mt7921e]
Read of size 8 at addr ffff88824a7d3b78 by task rmmod/11115
CPU: 28 PID: 11115 Comm: rmmod Tainted: G        W    L    5.17.0 #10
Hardware name: Micro-Star International Co., Ltd. MS-7D73/MPG B650I
EDGE WIFI (MS-7D73), BIOS 1.81 01/05/2024
Call Trace:
 <TASK>
 dump_stack_lvl+0x6f/0xa0
 print_address_description.constprop.0+0x1f/0x190
 ? mt7921_irq_handler+0xd8/0x100 [mt7921e]
 ? mt7921_irq_handler+0xd8/0x100 [mt7921e]
 kasan_report.cold+0x7f/0x11b
 ? mt7921_irq_handler+0xd8/0x100 [mt7921e]
 mt7921_irq_handler+0xd8/0x100 [mt7921e]
 free_irq+0x627/0xaa0
 devm_free_irq+0x94/0xd0
 ? devm_request_any_context_irq+0x160/0x160
 ? kobject_put+0x18d/0x4a0
 mt7921_pci_remove+0x153/0x190 [mt7921e]
 pci_device_remove+0xa2/0x1d0
 __device_release_driver+0x346/0x6e0
 driver_detach+0x1ef/0x2c0
 bus_remove_driver+0xe7/0x2d0
 ? __check_object_size+0x57/0x310
 pci_unregister_driver+0x26/0x250
 __do_sys_delete_module+0x307/0x510
 ? free_module+0x6a0/0x6a0
 ? fpregs_assert_state_consistent+0x4b/0xb0
 ? rcu_read_lock_sched_held+0x10/0x70
 ? syscall_enter_from_user_mode+0x20/0x70
 ? trace_hardirqs_on+0x1c/0x130
 do_syscall_64+0x5c/0x80
 ? trace_hardirqs_on_prepare+0x72/0x160
 ? do_syscall_64+0x68/0x80
 ? trace_hardirqs_on_prepare+0x72/0x160
 entry_SYSCALL_64_after_hwframe+0x44/0xae

Reported-by: Mikhail Gavrilov <mikhail.v.gavrilov@gmail.com>
Closes: https://lore.kernel.org/linux-wireless/CABXGCsOdvVwdLmSsC8TZ1jF0UOg_F_W3wqLECWX620PUkvNk=A@mail.gmail.com/
Fixes: 9270270 ("wifi: mt76: mt7921: fix PCI DMA hang after reboot")
Tested-by: Mikhail Gavrilov <mikhail.v.gavrilov@gmail.com>
Signed-off-by: Deren Wu <deren.wu@mediatek.com>
Signed-off-by: Felix Fietkau <nbd@nbd.name>

drivers/net/wireless/mediatek/mt76/mt7921/pci.c

@@ -387,6 +387,7 @@ static void mt7921_pci_remove(struct pci_dev *pdev)
 	struct mt792x_dev *dev = container_of(mdev, struct mt792x_dev, mt76);
 
 	mt7921e_unregister_device(dev);
+	set_bit(MT76_REMOVED, &mdev->phy.state);
 	devm_free_irq(&pdev->dev, pdev->irq, dev);
 	mt76_free_device(&dev->mt76);
 	pci_free_irq_vectors(pdev);

drivers/net/wireless/mediatek/mt76/mt792x_dma.c

@@ -12,6 +12,8 @@ irqreturn_t mt792x_irq_handler(int irq, void *dev_instance)
 {
 	struct mt792x_dev *dev = dev_instance;
 
+	if (test_bit(MT76_REMOVED, &dev->mt76.phy.state))
+		return IRQ_NONE;
 	mt76_wr(dev, dev->irq_map->host_irq_enable, 0);
 
 	if (!test_bit(MT76_STATE_INITIALIZED, &dev->mphy.state))