Linux: Bluetooth: hci_sync: Fix inquiry cache use-after-free

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

Bluetooth: hci_sync: Fix inquiry cache use-after-free

The sync command worker holds hdev->req_lock, but inquiry-cache updates and flushes use hdev->lock. Both hci_acl_create_conn_sync() and hci_stop_discovery_sync() look up entries and read their fields without taking hdev->lock.

After either lookup returns, a concurrent HCIINQUIRY ioctl can acquire hdev->lock and flush the cache, freeing the entry. The worker then reads the freed entry while preparing a create-connection or remote-name-cancel command. The list traversal also races with cache updates and removal.

KASAN reported these accesses:

BUG: KASAN: slab-use-after-free in hci_acl_create_conn_sync+0x5f1/0x650 Workqueue: hci0 hci_cmd_sync_work Call Trace: hci_acl_create_conn_sync+0x5f1/0x650 hci_cmd_sync_work+0x13c/0x290

Allocated by task 90: hci_inquiry_cache_update+0x3e6/0x7d0 hci_inquiry_result_evt+0x3cb/0x560

Freed by task 93: hci_inquiry_cache_flush+0x111/0x2b0 hci_inquiry+0x2f2/0x780 hci_sock_ioctl+0x269/0x5f0

BUG: KASAN: slab-use-after-free in hci_stop_discovery_sync+0x3b1/0x3c0 Workqueue: hci0 hci_cmd_sync_work Call Trace: hci_stop_discovery_sync+0x3b1/0x3c0 hci_cmd_sync_work+0x173/0x300

Allocated by task 86: hci_inquiry_cache_update+0x483/0x940 hci_inquiry_result_evt+0x3cb/0x560

Freed by task 91: hci_inquiry_cache_flush+0x13e/0x2f0 hci_inquiry+0x2f2/0x780 hci_sock_ioctl+0x269/0x5f0

Hold hdev->lock across each lookup and all reads from its result. Copy the remote address before unlocking so discovery cancellation does not retain a cache entry pointer. Release the lock before sending synchronous HCI commands, since their completion handlers may need the same lock.