Bluetooth: use RCU for hci_conn_params and iterate safely in hci_sync

hci_update_accept_list_sync iterates over hdev->pend_le_conns and
hdev->pend_le_reports, and waits for controller events in the loop body,
without holding hdev lock.

Meanwhile, these lists and the items may be modified e.g. by
le_scan_cleanup. This can invalidate the list cursor or any other item
in the list, resulting to invalid behavior (eg use-after-free).

Use RCU for the hci_conn_params action lists. Since the loop bodies in
hci_sync block and we cannot use RCU or hdev->lock for the whole loop,
copy list items first and then iterate on the copy. Only the flags field
is written from elsewhere, so READ_ONCE/WRITE_ONCE should guarantee we
read valid values.

Free params everywhere with hci_conn_params_free so the cleanup is
guaranteed to be done properly.

This fixes the following, which can be triggered e.g. by BlueZ new
mgmt-tester case "Add + Remove Device Nowait - Success", or by changing
hci_le_set_cig_params to always return false, and running iso-tester:

==================================================================
BUG: KASAN: slab-use-after-free in hci_update_passive_scan_sync (net/bluetooth/hci_sync.c:2536 net/bluetooth/hci_sync.c:2723 net/bluetooth/hci_sync.c:2841)
Read of size 8 at addr ffff888001265018 by task kworker/u3:0/32

Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.2-1.fc38 04/01/2014
Workqueue: hci0 hci_cmd_sync_work
Call Trace:
<TASK>
dump_stack_lvl (./arch/x86/include/asm/irqflags.h:134 lib/dump_stack.c:107)
print_report (mm/kasan/report.c:320 mm/kasan/report.c:430)
? __virt_addr_valid (./include/linux/mmzone.h:1915 ./include/linux/mmzone.h:2011 arch/x86/mm/physaddr.c:65)
? hci_update_passive_scan_sync (net/bluetooth/hci_sync.c:2536 net/bluetooth/hci_sync.c:2723 net/bluetooth/hci_sync.c:2841)
kasan_report (mm/kasan/report.c:538)
? hci_update_passive_scan_sync (net/bluetooth/hci_sync.c:2536 net/bluetooth/hci_sync.c:2723 net/bluetooth/hci_sync.c:2841)
hci_update_passive_scan_sync (net/bluetooth/hci_sync.c:2536 net/bluetooth/hci_sync.c:2723 net/bluetooth/hci_sync.c:2841)
? __pfx_hci_update_passive_scan_sync (net/bluetooth/hci_sync.c:2780)
? mutex_lock (kernel/locking/mutex.c:282)
? __pfx_mutex_lock (kernel/locking/mutex.c:282)
? __pfx_mutex_unlock (kernel/locking/mutex.c:538)
? __pfx_update_passive_scan_sync (net/bluetooth/hci_sync.c:2861)
hci_cmd_sync_work (net/bluetooth/hci_sync.c:306)
process_one_work (./arch/x86/include/asm/preempt.h:27 kernel/workqueue.c:2399)
worker_thread (./include/linux/list.h:292 kernel/workqueue.c:2538)
? __pfx_worker_thread (kernel/workqueue.c:2480)
kthread (kernel/kthread.c:376)
? __pfx_kthread (kernel/kthread.c:331)
ret_from_fork (arch/x86/entry/entry_64.S:314)
</TASK>

Allocated by task 31:
kasan_save_stack (mm/kasan/common.c:46)
kasan_set_track (mm/kasan/common.c:52)
__kasan_kmalloc (mm/kasan/common.c:374 mm/kasan/common.c:383)
hci_conn_params_add (./include/linux/slab.h:580 ./include/linux/slab.h:720 net/bluetooth/hci_core.c:2277)
hci_connect_le_scan (net/bluetooth/hci_conn.c:1419 net/bluetooth/hci_conn.c:1589)
hci_connect_cis (net/bluetooth/hci_conn.c:2266)
iso_connect_cis (net/bluetooth/iso.c:390)
iso_sock_connect (net/bluetooth/iso.c:899)
__sys_connect (net/socket.c:2003 net/socket.c:2020)
__x64_sys_connect (net/socket.c:2027)
do_syscall_64 (arch/x86/entry/common.c:50 arch/x86/entry/common.c:80)
entry_SYSCALL_64_after_hwframe (arch/x86/entry/entry_64.S:120)

Freed by task 15:
kasan_save_stack (mm/kasan/common.c:46)
kasan_set_track (mm/kasan/common.c:52)
kasan_save_free_info (mm/kasan/generic.c:523)
__kasan_slab_free (mm/kasan/common.c:238 mm/kasan/common.c:200 mm/kasan/common.c:244)
__kmem_cache_free (mm/slub.c:1807 mm/slub.c:3787 mm/slub.c:3800)
hci_conn_params_del (net/bluetooth/hci_core.c:2323)
le_scan_cleanup (net/bluetooth/hci_conn.c:202)
process_one_work (./arch/x86/include/asm/preempt.h:27 kernel/workqueue.c:2399)
worker_thread (./include/linux/list.h:292 kernel/workqueue.c:2538)
kthread (kernel/kthread.c:376)
ret_from_fork (arch/x86/entry/entry_64.S:314)
==================================================================

Fixes: e8907f7 ("Bluetooth: hci_sync: Make use of hci_cmd_sync_queue set 3")
Signed-off-by: Pauli Virtanen <pav@iki.fi>
Signed-off-by: Luiz Augusto von Dentz <luiz.von.dentz@intel.com>

Author: pv

include/net/bluetooth/hci_core.h

@@ -822,6 +822,7 @@ struct hci_conn_params {
 
 	struct hci_conn *conn;
 	bool explicit_connect;
+	/* Accessed without hdev->lock: */
 	hci_conn_flags_t flags;
 	u8  privacy_mode;
 };
@@ -1573,7 +1574,11 @@ struct hci_conn_params *hci_conn_params_add(struct hci_dev *hdev,
 					    bdaddr_t *addr, u8 addr_type);
 void hci_conn_params_del(struct hci_dev *hdev, bdaddr_t *addr, u8 addr_type);
 void hci_conn_params_clear_disabled(struct hci_dev *hdev);
+void hci_conn_params_free(struct hci_conn_params *param);
 
+void hci_pend_le_list_del_init(struct hci_conn_params *param);
+void hci_pend_le_list_add(struct hci_conn_params *param,
+			  struct list_head *list);
 struct hci_conn_params *hci_pend_le_action_lookup(struct list_head *list,
 						  bdaddr_t *addr,
 						  u8 addr_type);

net/bluetooth/hci_conn.c

@@ -118,7 +118,7 @@ static void hci_connect_le_scan_cleanup(struct hci_conn *conn, u8 status)
 	 */
 	params->explicit_connect = false;
 
-	list_del_init(&params->action);
+	hci_pend_le_list_del_init(params);
 
 	switch (params->auto_connect) {
 	case HCI_AUTO_CONN_EXPLICIT:
@@ -127,10 +127,10 @@ static void hci_connect_le_scan_cleanup(struct hci_conn *conn, u8 status)
 		return;
 	case HCI_AUTO_CONN_DIRECT:
 	case HCI_AUTO_CONN_ALWAYS:
-		list_add(&params->action, &hdev->pend_le_conns);
+		hci_pend_le_list_add(params, &hdev->pend_le_conns);
 		break;
 	case HCI_AUTO_CONN_REPORT:
-		list_add(&params->action, &hdev->pend_le_reports);
+		hci_pend_le_list_add(params, &hdev->pend_le_reports);
 		break;
 	default:
 		break;
@@ -1426,8 +1426,8 @@ static int hci_explicit_conn_params_set(struct hci_dev *hdev,
 	if (params->auto_connect == HCI_AUTO_CONN_DISABLED ||
 	    params->auto_connect == HCI_AUTO_CONN_REPORT ||
 	    params->auto_connect == HCI_AUTO_CONN_EXPLICIT) {
-		list_del_init(&params->action);
-		list_add(&params->action, &hdev->pend_le_conns);
+		hci_pend_le_list_del_init(params);
+		hci_pend_le_list_add(params, &hdev->pend_le_conns);
 	}
 
 	params->explicit_connect = true;

net/bluetooth/hci_core.c

@@ -2249,21 +2249,45 @@ struct hci_conn_params *hci_conn_params_lookup(struct hci_dev *hdev,
 	return NULL;
 }
 
-/* This function requires the caller holds hdev->lock */
+/* This function requires the caller holds hdev->lock or rcu_read_lock */
 struct hci_conn_params *hci_pend_le_action_lookup(struct list_head *list,
 						  bdaddr_t *addr, u8 addr_type)
 {
 	struct hci_conn_params *param;
 
-	list_for_each_entry(param, list, action) {
+	rcu_read_lock();
+
+	list_for_each_entry_rcu(param, list, action) {
 		if (bacmp(&param->addr, addr) == 0 &&
-		    param->addr_type == addr_type)
+		    param->addr_type == addr_type) {
+			rcu_read_unlock();
 			return param;
+		}
 	}
 
+	rcu_read_unlock();
+
 	return NULL;
 }
 
+/* This function requires the caller holds hdev->lock */
+void hci_pend_le_list_del_init(struct hci_conn_params *param)
+{
+	if (list_empty(&param->action))
+		return;
+
+	list_del_rcu(&param->action);
+	synchronize_rcu();
+	INIT_LIST_HEAD(&param->action);
+}
+
+/* This function requires the caller holds hdev->lock */
+void hci_pend_le_list_add(struct hci_conn_params *param,
+			  struct list_head *list)
+{
+	list_add_rcu(&param->action, list);
+}
+
 /* This function requires the caller holds hdev->lock */
 struct hci_conn_params *hci_conn_params_add(struct hci_dev *hdev,
 					    bdaddr_t *addr, u8 addr_type)
@@ -2297,14 +2321,15 @@ struct hci_conn_params *hci_conn_params_add(struct hci_dev *hdev,
 	return params;
 }
 
-static void hci_conn_params_free(struct hci_conn_params *params)
+void hci_conn_params_free(struct hci_conn_params *params)
 {
+	hci_pend_le_list_del_init(params);
+
 	if (params->conn) {
 		hci_conn_drop(params->conn);
 		hci_conn_put(params->conn);
 	}
 
-	list_del(&params->action);
 	list_del(&params->list);
 	kfree(params);
 }
@@ -2342,8 +2367,7 @@ void hci_conn_params_clear_disabled(struct hci_dev *hdev)
 			continue;
 		}
 
-		list_del(&params->list);
-		kfree(params);
+		hci_conn_params_free(params);
 	}
 
 	BT_DBG("All LE disabled connection parameters were removed");

net/bluetooth/hci_event.c

@@ -1564,7 +1564,7 @@ static u8 hci_cc_le_set_privacy_mode(struct hci_dev *hdev, void *data,
 
 	params = hci_conn_params_lookup(hdev, &cp->bdaddr, cp->bdaddr_type);
 	if (params)
-		params->privacy_mode = cp->mode;
+		WRITE_ONCE(params->privacy_mode, cp->mode);
 
 	hci_dev_unlock(hdev);
 
@@ -2804,8 +2804,8 @@ static void hci_cs_disconnect(struct hci_dev *hdev, u8 status)
 
 		case HCI_AUTO_CONN_DIRECT:
 		case HCI_AUTO_CONN_ALWAYS:
-			list_del_init(&params->action);
-			list_add(&params->action, &hdev->pend_le_conns);
+			hci_pend_le_list_del_init(params);
+			hci_pend_le_list_add(params, &hdev->pend_le_conns);
 			break;
 
 		default:
@@ -3423,8 +3423,8 @@ static void hci_disconn_complete_evt(struct hci_dev *hdev, void *data,
 
 		case HCI_AUTO_CONN_DIRECT:
 		case HCI_AUTO_CONN_ALWAYS:
-			list_del_init(&params->action);
-			list_add(&params->action, &hdev->pend_le_conns);
+			hci_pend_le_list_del_init(params);
+			hci_pend_le_list_add(params, &hdev->pend_le_conns);
 			hci_update_passive_scan(hdev);
 			break;
 
@@ -5962,7 +5962,7 @@ static void le_conn_complete_evt(struct hci_dev *hdev, u8 status,
 	params = hci_pend_le_action_lookup(&hdev->pend_le_conns, &conn->dst,
 					   conn->dst_type);
 	if (params) {
-		list_del_init(&params->action);
+		hci_pend_le_list_del_init(params);
 		if (params->conn) {
 			hci_conn_drop(params->conn);
 			hci_conn_put(params->conn);

net/bluetooth/hci_sync.c

@@ -2160,15 +2160,23 @@ static int hci_le_del_accept_list_sync(struct hci_dev *hdev,
 	return 0;
 }
 
+struct conn_params {
+	bdaddr_t addr;
+	u8 addr_type;
+	hci_conn_flags_t flags;
+	u8 privacy_mode;
+};
+
 /* Adds connection to resolve list if needed.
  * Setting params to NULL programs local hdev->irk
  */
 static int hci_le_add_resolve_list_sync(struct hci_dev *hdev,
-					struct hci_conn_params *params)
+					struct conn_params *params)
 {
 	struct hci_cp_le_add_to_resolv_list cp;
 	struct smp_irk *irk;
 	struct bdaddr_list_with_irk *entry;
+	struct hci_conn_params *p;
 
 	if (!use_ll_privacy(hdev))
 		return 0;
@@ -2203,6 +2211,16 @@ static int hci_le_add_resolve_list_sync(struct hci_dev *hdev,
 	/* Default privacy mode is always Network */
 	params->privacy_mode = HCI_NETWORK_PRIVACY;
 
+	rcu_read_lock();
+	p = hci_pend_le_action_lookup(&hdev->pend_le_conns,
+				      &params->addr, params->addr_type);
+	if (!p)
+		p = hci_pend_le_action_lookup(&hdev->pend_le_reports,
+					      &params->addr, params->addr_type);
+	if (p)
+		WRITE_ONCE(p->privacy_mode, HCI_NETWORK_PRIVACY);
+	rcu_read_unlock();
+
 done:
 	if (hci_dev_test_flag(hdev, HCI_PRIVACY))
 		memcpy(cp.local_irk, hdev->irk, 16);
@@ -2215,7 +2233,7 @@ static int hci_le_add_resolve_list_sync(struct hci_dev *hdev,
 
 /* Set Device Privacy Mode. */
 static int hci_le_set_privacy_mode_sync(struct hci_dev *hdev,
-					struct hci_conn_params *params)
+					struct conn_params *params)
 {
 	struct hci_cp_le_set_privacy_mode cp;
 	struct smp_irk *irk;
@@ -2240,6 +2258,8 @@ static int hci_le_set_privacy_mode_sync(struct hci_dev *hdev,
 	bacpy(&cp.bdaddr, &irk->bdaddr);
 	cp.mode = HCI_DEVICE_PRIVACY;
 
+	/* Note: params->privacy_mode is not updated since it is a copy */
+
 	return __hci_cmd_sync_status(hdev, HCI_OP_LE_SET_PRIVACY_MODE,
 				     sizeof(cp), &cp, HCI_CMD_TIMEOUT);
 }
@@ -2249,7 +2269,7 @@ static int hci_le_set_privacy_mode_sync(struct hci_dev *hdev,
  * properly set the privacy mode.
  */
 static int hci_le_add_accept_list_sync(struct hci_dev *hdev,
-				       struct hci_conn_params *params,
+				       struct conn_params *params,
 				       u8 *num_entries)
 {
 	struct hci_cp_le_add_to_accept_list cp;
@@ -2447,6 +2467,52 @@ struct sk_buff *hci_read_local_oob_data_sync(struct hci_dev *hdev,
 	return __hci_cmd_sync_sk(hdev, opcode, 0, NULL, 0, HCI_CMD_TIMEOUT, sk);
 }
 
+static struct conn_params *conn_params_copy(struct list_head *list, size_t *n)
+{
+	struct hci_conn_params *params;
+	struct conn_params *p;
+	size_t i;
+
+	rcu_read_lock();
+
+	i = 0;
+	list_for_each_entry_rcu(params, list, action)
+		++i;
+	*n = i;
+
+	rcu_read_unlock();
+
+	p = kvcalloc(*n, sizeof(struct conn_params), GFP_KERNEL);
+	if (!p)
+		return NULL;
+
+	rcu_read_lock();
+
+	i = 0;
+	list_for_each_entry_rcu(params, list, action) {
+		/* Racing adds are handled in next scan update */
+		if (i >= *n)
+			break;
+
+		/* No hdev->lock, but: addr, addr_type are immutable.
+		 * privacy_mode is only written by us or in
+		 * hci_cc_le_set_privacy_mode that we wait for.
+		 * We should be idempotent so MGMT updating flags
+		 * while we are processing is OK.
+		 */
+		bacpy(&p[i].addr, &params->addr);
+		p[i].addr_type = params->addr_type;
+		p[i].flags = READ_ONCE(params->flags);
+		p[i].privacy_mode = READ_ONCE(params->privacy_mode);
+		++i;
+	}
+
+	rcu_read_unlock();
+
+	*n = i;
+	return p;
+}
+
 /* Device must not be scanning when updating the accept list.
  *
  * Update is done using the following sequence:
@@ -2466,11 +2532,12 @@ struct sk_buff *hci_read_local_oob_data_sync(struct hci_dev *hdev,
  */
 static u8 hci_update_accept_list_sync(struct hci_dev *hdev)
 {
-	struct hci_conn_params *params;
+	struct conn_params *params;
 	struct bdaddr_list *b, *t;
 	u8 num_entries = 0;
 	bool pend_conn, pend_report;
 	u8 filter_policy;
+	size_t i, n;
 	int err;
 
 	/* Pause advertising if resolving list can be used as controllers
@@ -2504,6 +2571,7 @@ static u8 hci_update_accept_list_sync(struct hci_dev *hdev)
 		if (hci_conn_hash_lookup_le(hdev, &b->bdaddr, b->bdaddr_type))
 			continue;
 
+		/* Pointers not dereferenced, no locks needed */
 		pend_conn = hci_pend_le_action_lookup(&hdev->pend_le_conns,
 						      &b->bdaddr,
 						      b->bdaddr_type);
@@ -2532,23 +2600,50 @@ static u8 hci_update_accept_list_sync(struct hci_dev *hdev)
 	 * available accept list entries in the controller, then
 	 * just abort and return filer policy value to not use the
 	 * accept list.
+	 *
+	 * The list and params may be mutated while we wait for events,
+	 * so make a copy and iterate it.
 	 */
-	list_for_each_entry(params, &hdev->pend_le_conns, action) {
-		err = hci_le_add_accept_list_sync(hdev, params, &num_entries);
-		if (err)
+
+	params = conn_params_copy(&hdev->pend_le_conns, &n);
+	if (!params) {
+		err = -ENOMEM;
+		goto done;
+	}
+
+	for (i = 0; i < n; ++i) {
+		err = hci_le_add_accept_list_sync(hdev, &params[i],
+						  &num_entries);
+		if (err) {
+			kvfree(params);
 			goto done;
+		}
 	}
 
+	kvfree(params);
+
 	/* After adding all new pending connections, walk through
 	 * the list of pending reports and also add these to the
 	 * accept list if there is still space. Abort if space runs out.
 	 */
-	list_for_each_entry(params, &hdev->pend_le_reports, action) {
-		err = hci_le_add_accept_list_sync(hdev, params, &num_entries);
-		if (err)
+
+	params = conn_params_copy(&hdev->pend_le_reports, &n);
+	if (!params) {
+		err = -ENOMEM;
+		goto done;
+	}
+
+	for (i = 0; i < n; ++i) {
+		err = hci_le_add_accept_list_sync(hdev, &params[i],
+						  &num_entries);
+		if (err) {
+			kvfree(params);
 			goto done;
+		}
 	}
 
+	kvfree(params);
+
 	/* Use the allowlist unless the following conditions are all true:
 	 * - We are not currently suspending
 	 * - There are 1 or more ADV monitors registered and it's not offloaded
@@ -4837,12 +4932,12 @@ static void hci_pend_le_actions_clear(struct hci_dev *hdev)
 	struct hci_conn_params *p;
 
 	list_for_each_entry(p, &hdev->le_conn_params, list) {
+		hci_pend_le_list_del_init(p);
 		if (p->conn) {
 			hci_conn_drop(p->conn);
 			hci_conn_put(p->conn);
 			p->conn = NULL;
 		}
-		list_del_init(&p->action);
 	}
 
 	BT_DBG("All LE pending actions cleared");