From 281ddc4e01ab54cab07995f2a1b72cf81bf90eb5 Mon Sep 17 00:00:00 2001 From: Cen Zhang Date: Thu, 29 Oct 2026 21:12:26 +0800 Subject: [PATCH] Bluetooth: hci_core: Keep link-key filtering inside RCU hci_find_link_key() must keep the matching link key allocated while it checks the key against the blocked-key list. It currently leaves the key-list RCU read-side section before passing k->val to hci_is_blocked_key(). That helper's own RCU section protects the blocked-key list, but it cannot keep an unlinked link key from being reclaimed. The SMP receive path calls the finder without hdev->lock: Secure Connections key distribution over BR/EDR reaches it through smp_distribute_keys() and sc_generate_ltk(). With a stored peer link key and a link-key entry in the blocked-key list, MGMT_OP_LOAD_LINK_KEYS can free the selected key before the comparison: HCI RX worker (SMP) Management / RCU reclamation hci_find_link_key() rcu_read_lock() select k rcu_read_unlock() load_link_keys() hci_dev_lock(hdev) hci_link_keys_clear(hdev) list_del_rcu(), kfree_rcu() hci_dev_unlock(hdev) grace period ends, k is freed hci_is_blocked_key(hdev, ..., k->val) memcmp() reads the freed key Keep the RCU read-side section active through the blocked-key comparison and the warning that prints k->bdaddr, and release it before returning on both matched-key paths. hci_find_ltk() already handles its blocked-key check this way. KASAN reported this on a test kernel whose scheduling hook paused the receive worker after the lookup until the key had been freed. KASAN report as below: ================================================================== BUG: KASAN: slab-use-after-free in hci_is_blocked_key+0x2db/0x300 Read of size 1 at addr ffff88810b5f89a7 by task kworker/u17:0/502 CPU: 1 UID: 0 PID: 502 Comm: kworker/u17:0 Not tainted 7.2.0-rc6-pmb-bt-functional-v1+ #5 PREEMPT(lazy) Hardware name: QEMU Ubuntu 24.04 PC v2 (i440FX + PIIX, arch_caps fix, 1996), BIOS 1.16.3-debian-1.16.3-2 04/01/2014 Workqueue: hci1 hci_rx_work Call Trace: dump_stack_lvl+0x93/0xd0 print_report+0xce/0x630 ? hci_is_blocked_key+0x2db/0x300 ? srso_alias_return_thunk+0x5/0xfbef5 ? __virt_addr_valid+0x20d/0x410 ? hci_is_blocked_key+0x2db/0x300 kasan_report+0xe0/0x110 ? hci_is_blocked_key+0x2db/0x300 hci_is_blocked_key+0x2db/0x300 hci_find_link_key+0x12e/0x400 smp_distribute_keys+0x1830/0x2950 ? trace_hardirqs_on+0x18/0x160 ? srso_alias_return_thunk+0x5/0xfbef5 ? queue_delayed_work_on+0xb3/0xf0 ? __pfx_smp_distribute_keys+0x10/0x10 ? __pfx_smp_send_cmd.isra.0+0x10/0x10 ? __cancel_work+0x1b0/0x290 ? __entry_text_end+0x1020f7/0x1020f9 ? lockdep_hardirqs_on_prepare+0xea/0x1a0 ? srso_alias_return_thunk+0x5/0xfbef5 ? __asan_memset+0x23/0x50 ? smp_recv_cb+0x12c7/0x8d80 ? srso_alias_return_thunk+0x5/0xfbef5 smp_recv_cb+0x12c7/0x8d80 ? __pfx_smp_recv_cb+0x10/0x10 ? __pfx___might_resched+0x10/0x10 ? srso_alias_return_thunk+0x5/0xfbef5 ? stack_depot_save_flags+0x29/0x9a0 ? srso_alias_return_thunk+0x5/0xfbef5 ? __mutex_lock+0x182c/0x2590 ? kasan_save_stack+0x42/0x60 ? l2cap_recv_frame+0x9ef/0x8830 ? __kasan_slab_free+0x5f/0x80 ? kmem_cache_free+0x242/0x580 ? kfree_skbmem+0x15e/0x1d0 ? sk_skb_reason_drop+0x12f/0x490 ? hci_event_packet+0x556/0xc70 ? hci_rx_work+0x367/0xf00 ? process_one_work+0x908/0x19c0 ? worker_thread+0x65c/0xe40 ? __pfx___mutex_lock+0x10/0x10 ? __lock_acquire+0x466/0x2260 ? __pfx_l2cap_chan_hold_unless_zero+0x10/0x10 ? l2cap_recv_frame+0x13cc/0x8830 ? __pfx_smp_recv_cb+0x10/0x10 l2cap_recv_frame+0x13cc/0x8830 ? srso_alias_return_thunk+0x5/0xfbef5 ? __mutex_lock+0x182c/0x2590 ? __pfx_l2cap_recv_frame+0x10/0x10 ? srso_alias_return_thunk+0x5/0xfbef5 ? find_held_lock+0x2b/0x80 ? l2cap_recv_acldata+0x1eb/0x10e0 ? __pfx___mutex_lock+0x10/0x10 ? srso_alias_return_thunk+0x5/0xfbef5 ? __mutex_unlock_slowpath+0x147/0x920 ? __pfx_l2cap_conn_hold_unless_zero+0x10/0x10 ? __pfx_hci_conn_enter_active_mode+0x10/0x10 ? l2cap_recv_acldata+0x13d/0x10e0 ? srso_alias_return_thunk+0x5/0xfbef5 l2cap_recv_acldata+0xe9f/0x10e0 ? srso_alias_return_thunk+0x5/0xfbef5 hci_rx_work+0x5a6/0xf00 ? srso_alias_return_thunk+0x5/0xfbef5 process_one_work+0x908/0x19c0 ? __pfx_process_one_work+0x10/0x10 ? srso_alias_return_thunk+0x5/0xfbef5 ? lock_is_held_type+0x8f/0x100 ? srso_alias_return_thunk+0x5/0xfbef5 worker_thread+0x65c/0xe40 ? __pfx_worker_thread+0x10/0x10 kthread+0x34f/0x460 ? srso_alias_return_thunk+0x5/0xfbef5 ? __pfx_kthread+0x10/0x10 ret_from_fork+0x659/0x940 ? __pfx_ret_from_fork+0x10/0x10 ? srso_alias_return_thunk+0x5/0xfbef5 ? __switch_to+0x74f/0xf80 ? __pfx_kthread+0x10/0x10 ret_from_fork_asm+0x1a/0x30 Allocated by task 504: kasan_save_stack+0x33/0x60 kasan_save_track+0x14/0x30 __kasan_kmalloc+0xaa/0xb0 __kmalloc_cache_noprof+0x251/0x610 hci_add_link_key+0x474/0x840 hci_link_key_notify_evt+0x492/0xce0 hci_event_packet+0x894/0xc70 hci_rx_work+0x367/0xf00 process_one_work+0x908/0x19c0 worker_thread+0x65c/0xe40 kthread+0x34f/0x460 ret_from_fork+0x659/0x940 ret_from_fork_asm+0x1a/0x30 Freed by task 29: kasan_save_stack+0x33/0x60 kasan_save_track+0x14/0x30 kasan_save_free_info+0x3b/0x60 __kasan_slab_free+0x5f/0x80 __rcu_free_sheaf_prepare+0x65/0x2a0 rcu_free_sheaf_nobarn+0x1d/0x50 rcu_core+0x661/0x1d10 handle_softirqs+0x201/0x930 run_ksoftirqd+0x33/0x60 smpboot_thread_fn+0x3bd/0x9a0 kthread+0x34f/0x460 ret_from_fork+0x659/0x940 ret_from_fork_asm+0x1a/0x30 The buggy address belongs to the object at ffff88810b5f8980 which belongs to the cache kmalloc-64 of size 64 The buggy address is located 39 bytes inside of freed 64-byte region [ffff88810b5f8980, ffff88810b5f89c0) The buggy address belongs to the physical page: page: refcount:0 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x10b5f8 flags: 0x200000000000000(node=0|zone=2) page_type: f5(slab) raw: 0200000000000000 ffff8881000428c0 dead000000000100 dead000000000122 raw: 0000000000000000 0000000000200020 00000000f5000000 0000000000000000 page dumped because: kasan: bad access detected Memory state around the buggy address: ffff88810b5f8880: fa fb fb fb fb fb fb fb fc fc fc fc fc fc fc fc ffff88810b5f8900: 00 00 00 00 00 00 00 fc fc fc fc fc fc fc fc fc >ffff88810b5f8980: fa fb fb fb fb fb fb fb fc fc fc fc fc fc fc fc ^ ffff88810b5f8a00: fa fb fb fb fb fb fb fb fc fc fc fc fc fc fc fc ffff88810b5f8a80: fa fb fb fb fb fb fb fb fc fc fc fc fc fc fc fc ================================================================== Fixes: 600a87490ff9 ("Bluetooth: Implementation of MGMT_OP_SET_BLOCKED_KEYS.") Assisted-by: LLM Signed-off-by: Cen Zhang Signed-off-by: Luiz Augusto von Dentz --- net/bluetooth/hci_core.c | 5 ++--- 1 file changed, 2 insertions(+), 3 deletions(-) diff --git a/net/bluetooth/hci_core.c b/net/bluetooth/hci_core.c index 55fc64db495a..a299aea1dd09 100644 --- a/net/bluetooth/hci_core.c +++ b/net/bluetooth/hci_core.c @@ -1075,17 +1075,16 @@ struct link_key *hci_find_link_key(struct hci_dev *hdev, bdaddr_t *bdaddr) rcu_read_lock(); list_for_each_entry_rcu(k, &hdev->link_keys, list) { if (bacmp(bdaddr, &k->bdaddr) == 0) { - rcu_read_unlock(); - if (hci_is_blocked_key(hdev, HCI_BLOCKED_KEY_TYPE_LINKKEY, k->val)) { bt_dev_warn_ratelimited(hdev, "Link key blocked for %pMR", &k->bdaddr); - return NULL; + k = NULL; } + rcu_read_unlock(); return k; } }