[PATCH] Bluetooth: hci_sync: Fix scan response data UAF

[Chengfeng Ye <nicoyip.dev@gmail.com>]

eir_create_scan_rsp() calls hci_find_adv_instance(), whose return value is
valid only while hdev->lock is held.  After advertising setup was moved to
hci_cmd_sync_work, neither scan response data builder held that lock.
hci_set_ext_scan_rsp_data_sync() also kept the returned pointer while
waiting for the controller and wrote scan_rsp_changed through it afterward.

An advertising termination event can therefore interleave as follows:

  hci_cmd_sync_work                 hci_rx_work
  hci_find_adv_instance()
  __hci_cmd_sync_status()
    wait for controller reply       hci_dev_lock()
                                    hci_remove_adv_instance()
                                      kfree(adv)
  adv->scan_rsp_changed = false

KASAN reported:

  BUG: KASAN: slab-use-after-free in hci_set_ext_scan_rsp_data_sync+0x2e1/0x300
  Write of size 1 at addr ffff88810a45d21d by task kworker/u17:0/88
  Workqueue: hci0 hci_cmd_sync_work
  Call Trace:
   hci_set_ext_scan_rsp_data_sync+0x2e1/0x300
   hci_schedule_adv_instance_sync+0x390/0x4c0
   hci_cmd_sync_work+0x173/0x300
  Allocated by task 87:
   hci_add_adv_instance+0x538/0xac0
   add_advertising+0x885/0x1160
  Freed by task 89:
   kfree+0x131/0x3c0
   hci_remove_adv_instance+0x1d8/0x3b0
   hci_le_ext_adv_term_evt+0x17b/0x730

Hold hdev->lock while looking up the instance, building the scan
response, and clearing its dirty bit.  Clear the bit before waiting for
the controller so no adv_info pointer survives the wait, and restore it
under the lock if the command fails.  This also preserves an update that
races with a successful command because that update sets the bit again.
Protect the legacy scan response builder with the same lock.

Fixes: cba6b758711c ("Bluetooth: hci_sync: Make use of hci_cmd_sync_queue set 2")
Cc: stable@vger.kernel.org
Signed-off-by: Chengfeng Ye <nicoyip.dev@gmail.com>
---
 net/bluetooth/hci_sync.c | 32 +++++++++++++++++++++++++++-----
 1 file changed, 27 insertions(+), 5 deletions(-)

diff --git a/net/bluetooth/hci_sync.c b/net/bluetooth/hci_sync.c
index 532534bc601c..8c69a98c71e8 100644
--- a/net/bluetooth/hci_sync.c
+++ b/net/bluetooth/hci_sync.c
@@ -1490,9 +1490,13 @@ static int hci_set_ext_scan_rsp_data_sync(struct hci_dev *hdev, u8 instance)
 	int err;
 
 	if (instance) {
+		hci_dev_lock(hdev);
+
 		adv = hci_find_adv_instance(hdev, instance);
-		if (!adv || !adv->scan_rsp_changed)
+		if (!adv || !adv->scan_rsp_changed) {
+			hci_dev_unlock(hdev);
 			return 0;
+		}
 	}
 
 	len = eir_create_scan_rsp(hdev, instance, pdu->data);
@@ -1502,15 +1506,27 @@ static int hci_set_ext_scan_rsp_data_sync(struct hci_dev *hdev, u8 instance)
 	pdu->operation = LE_SET_ADV_DATA_OP_COMPLETE;
 	pdu->frag_pref = LE_SET_ADV_DATA_NO_FRAG;
 
+	if (adv) {
+		adv->scan_rsp_changed = false;
+		hci_dev_unlock(hdev);
+	}
+
 	err = __hci_cmd_sync_status(hdev, HCI_OP_LE_SET_EXT_SCAN_RSP_DATA,
 				    struct_size(pdu, data, len), pdu,
 				    HCI_CMD_TIMEOUT);
-	if (err)
+	if (err) {
+		if (instance) {
+			hci_dev_lock(hdev);
+			adv = hci_find_adv_instance(hdev, instance);
+			if (adv)
+				adv->scan_rsp_changed = true;
+			hci_dev_unlock(hdev);
+		}
+
 		return err;
+	}
 
-	if (adv) {
-		adv->scan_rsp_changed = false;
-	} else {
+	if (!instance) {
 		memcpy(hdev->scan_rsp_data, pdu->data, len);
 		hdev->scan_rsp_data_len = len;
 	}
@@ -1525,8 +1541,14 @@ static int __hci_set_scan_rsp_data_sync(struct hci_dev *hdev, u8 instance)
 
 	memset(&cp, 0, sizeof(cp));
 
+	if (instance)
+		hci_dev_lock(hdev);
+
 	len = eir_create_scan_rsp(hdev, instance, cp.data);
 
+	if (instance)
+		hci_dev_unlock(hdev);
+
 	if (hdev->scan_rsp_data_len == len &&
 	    !memcmp(cp.data, hdev->scan_rsp_data, len))
 		return 0;
-- 
2.43.0