regulator: core: fix UAF in destroy_regulator()

I got a UAF report as following:

==================================================================
BUG: KASAN: use-after-free in __lock_acquire+0x935/0x2060
Read of size 8 at addr ffff88810e838220 by task python3/268
Call Trace:
 <TASK>
 dump_stack_lvl+0x67/0x83
 print_report+0x178/0x4b0
 kasan_report+0x90/0x190
 __lock_acquire+0x935/0x2060
 lock_acquire+0x156/0x400
 _raw_spin_lock+0x2a/0x40
 lockref_get+0x11/0x30
 simple_recursive_removal+0x41/0x440
 debugfs_remove.part.12+0x32/0x50
 debugfs_remove+0x29/0x30
 _regulator_put.cold.54+0x3e/0x27f
 regulator_put+0x1f/0x30
 release_nodes+0x6a/0xa0
 devres_release_all+0xf8/0x150

Allocated by task 37:
 kasan_save_stack+0x1c/0x40
 kasan_set_track+0x21/0x30
 __kasan_slab_alloc+0x5d/0x70
 slab_post_alloc_hook+0x62/0x510
 kmem_cache_alloc_lru+0x222/0x5a0
 __d_alloc+0x31/0x440
 d_alloc+0x30/0xf0
 d_alloc_parallel+0xc4/0xd20
 __lookup_slow+0x15e/0x2f0
 lookup_one_len+0x13a/0x150
 start_creating+0xea/0x190
 debugfs_create_dir+0x1e/0x210
 create_regulator+0x254/0x4e0
 _regulator_get+0x2a1/0x467
 _devm_regulator_get+0x5a/0xb0
 regulator_virtual_probe+0xb9/0x1a0

Freed by task 30:
 kasan_save_stack+0x1c/0x40
 kasan_set_track+0x21/0x30
 kasan_save_free_info+0x2a/0x50
 __kasan_slab_free+0x102/0x190
 kmem_cache_free+0xf6/0x600
 rcu_core+0x54c/0x12b0
 __do_softirq+0xf2/0x5e3

Last potentially related work creation:
 kasan_save_stack+0x1c/0x40
 __kasan_record_aux_stack+0x98/0xb0
 call_rcu+0x42/0x700
 dentry_free+0x6c/0xd0
 __dentry_kill+0x23b/0x2d0
 dput.part.31+0x431/0x780
 simple_recursive_removal+0xa9/0x440
 debugfs_remove.part.12+0x32/0x50
 debugfs_remove+0x29/0x30
 regulator_unregister+0xe3/0x230
 release_nodes+0x6a/0xa0

==================================================================

Here is how happened:

processor A					processor B
regulator_register()
  rdev_init_debugfs()
    rdev->debugfs = debugfs_create_dir()
						devm_regulator_get()
						  rdev = regulator_dev_lookup()
						  create_regulator(rdev)
						    // using rdev->debugfs as parent
						    debugfs_create_dir(rdev->debugfs)

mfd_remove_devices_fn()
  release_nodes()
    regulator_unregister()
      // free rdev->debugfs
      debugfs_remove_recursive(rdev->debugfs)
						release_nodes()
						  destroy_regulator()
						    debugfs_remove_recursive() <- causes UAF

In devm_regulator_get(), after getting rdev, the refcount
is get, so fix this by moving debugfs_remove_recursive()
to regulator_dev_release(), then it can be proctected by
the refcount, the 'rdev->debugfs' can not be freed until
the refcount is 0.

Fixes: 5de7051 ("regulator: Add basic per consumer debugfs")
Signed-off-by: Yang Yingliang <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Mark Brown <[email protected]>

Author: Yang Yingliang

drivers/regulator/core.c

@@ -5149,6 +5149,7 @@ static void regulator_dev_release(struct device *dev)
 {
 	struct regulator_dev *rdev = dev_get_drvdata(dev);
 
+	debugfs_remove_recursive(rdev->debugfs);
 	kfree(rdev->constraints);
 	of_node_put(rdev->dev.of_node);
 	kfree(rdev);
@@ -5676,7 +5677,6 @@ void regulator_unregister(struct regulator_dev *rdev)
 
 	mutex_lock(&regulator_list_mutex);
 
-	debugfs_remove_recursive(rdev->debugfs);
 	WARN_ON(rdev->open_count);
 	regulator_remove_coupling(rdev);
 	unset_regulator_supplies(rdev);