[PATCH 2/2] Bluetooth: hci_core: Initialize advertising RPA work only once

[Cen Zhang <zzzccc427@gmail.com>]

hci_add_adv_instance() also updates existing instances and calls
INIT_DELAYED_WORK() on their rpa_expired_cb every time, even when the
work is pending or running. cancel_delayed_work_sync() then no longer
finds the work, so hci_remove_adv_instance() can free the instance
under it:

  hdev->workqueue                 MGMT_OP_ADD_EXT_ADV_PARAMS
  adv_instance_rpa_expired()
                                  hci_dev_lock(hdev)
                                  hci_add_adv_instance()
                                    INIT_DELAYED_WORK()
                                  mgmt_pending_new() fails
                                  hci_remove_adv_instance()
                                    cancel_delayed_work_sync()
                                      returns without waiting
                                    kfree(adv)
                                  hci_dev_unlock(hdev)
    adv->rpa_expired = true

The work has been initialized on every update since it was added.
Initialize it only when the instance is allocated.

KASAN report as below:

    BUG: KASAN: slab-use-after-free in adv_instance_rpa_expired+0x139/0x160
    Write of size 1 at addr ffff888108d84b2e by task kworker/u17:0/504

    Workqueue: hci0 adv_instance_rpa_expired
    Call Trace:
     adv_instance_rpa_expired+0x139/0x160

    Allocated by task 560:
     hci_add_adv_instance+0x68d/0x9d0
     add_ext_adv_params+0x4d4/0xb60
     hci_sock_sendmsg+0x128b/0x22e0

    Freed by task 594:
     kfree+0x307/0x580
     hci_remove_adv_instance+0x230/0x540
     add_ext_adv_params+0xa43/0xb60
     hci_sock_sendmsg+0x128b/0x22e0

    Last potentially related work creation:
     insert_work+0x37/0x210
     __queue_work+0xaba/0x1270
     call_timer_fn+0x171/0x500

    The buggy address belongs to the object at ffff888108d84800
     which belongs to the cache kmalloc-1k of size 1024
    The buggy address is located 814 bytes inside of
     freed 1024-byte region [ffff888108d84800, ffff888108d84c00)

Fixes: a73c046a2869 ("Bluetooth: Implement Set ADV set random address")
Signed-off-by: Cen Zhang <zzzccc427@gmail.com>
---
Assisted-by: LLM

 net/bluetooth/hci_core.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/net/bluetooth/hci_core.c b/net/bluetooth/hci_core.c
index 2a29cfdee9728..79573193471bc 100644
--- a/net/bluetooth/hci_core.c
+++ b/net/bluetooth/hci_core.c
@@ -1796,6 +1796,9 @@ struct adv_info *hci_add_adv_instance(struct hci_dev *hdev, u8 instance,
 		if (!adv)
 			return ERR_PTR(-ENOMEM);
 
+		INIT_DELAYED_WORK(&adv->rpa_expired_cb,
+				  adv_instance_rpa_expired);
+
 		adv->pending = true;
 		adv->instance = instance;
 
@@ -1832,8 +1835,6 @@ struct adv_info *hci_add_adv_instance(struct hci_dev *hdev, u8 instance,
 	else
 		adv->duration = duration;
 
-	INIT_DELAYED_WORK(&adv->rpa_expired_cb, adv_instance_rpa_expired);
-
 	BT_DBG("%s for %dMR", hdev->name, instance);
 
 	return adv;