[PATCH] Bluetooth: hci_conn: Lock parent access during enhanced SCO setup

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

Bluetooth: hci_conn: Lock parent access during enhanced SCO setup

hci_enhanced_setup_sync() runs on the request workqueue without the
hci_dev_lock held by its caller when setup was queued. Its CVSD
capability check and find_next_esco_param() dereference conn->parent
while the receive workqueue can unlink and release that parent.

The following interleaving can cause a use-after-free:

  hci_enhanced_setup_sync()       hci_disconn_complete_evt()
  load conn->parent
                                 hci_dev_lock()
                                 hci_conn_del(ACL parent)
                                   unlink SCO child
                                   drop link's parent reference
                                   clear child->parent
                                   release ACL parent
                                     bt_link_release()
                                       kfree(parent)
                                 hci_dev_unlock()
  read parent->features[0][3]

The reference held for the queued SCO child does not keep its ACL parent
alive after unlinking. Commit 42de40abe25d ("Bluetooth: hci_conn: fix the
SCO setup context lifetime") protects the child stored in the queued
context, but leaves these parent accesses unprotected.

With a 40 ms diagnostic delay after loading conn->parent, an instrumented
kernel based on fd179f8a05be, which already contains 42de40abe25d,
reported:

  BUG: KASAN: slab-use-after-free in hci_enhanced_setup_sync+0xda5/0xdf0
  Read of size 1 at addr ffff888102204047 by task kworker/u17:0/93
  Call Trace:
   hci_enhanced_setup_sync+0xda5/0xdf0
   hci_cmd_sync_work+0x13c/0x290
   process_one_work+0x6b4/0x10e0

  Allocated by task 92:
   __hci_conn_add+0x304/0x1df0
   hci_connect_acl+0x349/0x3e0
   hci_connect_sco+0x3b/0x9a0
   sco_sock_connect+0x475/0xca0

  Freed by task 94:
   kfree+0x121/0x3c0
   bt_link_release+0x79/0xa0
   device_release+0xc8/0x240
   kobject_put+0x14d/0x280
   hci_conn_del+0x524/0xe30
   hci_disconn_complete_evt+0x403/0x8c0
   hci_event_packet+0x71b/0xb20
   hci_rx_work+0x293/0x730

The accessed address is 71 bytes into the freed ACL parent, at its
features[0][3] byte; the queued SCO child is a different object. The
diagnostic preserves the loaded parent across the delay, matching the
unmodified compiled capability check, and does not change the parent
references or teardown path.

Hold hci_dev_lock() across the codec switch, including every call to
find_next_esco_param(), and release it on all selection errors. Keep
configure_datapath_sync() outside the critical section because it waits
for HCI events. Preserve parameter selection and existing return values.

Fixes: e07a06b4eb41 ("Bluetooth: Convert SCO configure_datapath to hci_sync")
Cc: stable@vger.kernel.org
Assisted-by: GPT-6-Astra
Signed-off-by: Chengfeng Ye <nicoyip.dev@gmail.com>
---
 net/bluetooth/hci_conn.c | 18 +++++++++++++-----
 1 file changed, 13 insertions(+), 5 deletions(-)

diff --git a/net/bluetooth/hci_conn.c b/net/bluetooth/hci_conn.c
index 96195d2fd10f..cf44452e0766 100644
--- a/net/bluetooth/hci_conn.c
+++ b/net/bluetooth/hci_conn.c
@@ -302,11 +302,13 @@ static int hci_enhanced_setup_sync(struct hci_dev *hdev, void *data)
 	cp.tx_bandwidth   = cpu_to_le32(0x00001f40);
 	cp.rx_bandwidth   = cpu_to_le32(0x00001f40);
 
+	hci_dev_lock(hdev);
+
 	switch (conn->codec.id) {
 	case BT_CODEC_MSBC:
 		if (!find_next_esco_param(conn, esco_param_msbc,
 					  ARRAY_SIZE(esco_param_msbc)))
-			return -EINVAL;
+			goto unlock;
 
 		param = &esco_param_msbc[conn->attempt - 1];
 		cp.tx_coding_format.id = 0x05;
@@ -332,7 +334,7 @@ static int hci_enhanced_setup_sync(struct hci_dev *hdev, void *data)
 	case BT_CODEC_TRANSPARENT:
 		if (!find_next_esco_param(conn, esco_param_msbc,
 					  ARRAY_SIZE(esco_param_msbc)))
-			return -EINVAL;
+			goto unlock;
 
 		param = &esco_param_msbc[conn->attempt - 1];
 		cp.tx_coding_format.id = 0x03;
@@ -359,11 +361,11 @@ static int hci_enhanced_setup_sync(struct hci_dev *hdev, void *data)
 		if (conn->parent && lmp_esco_capable(conn->parent)) {
 			if (!find_next_esco_param(conn, esco_param_cvsd,
 						  ARRAY_SIZE(esco_param_cvsd)))
-				return -EINVAL;
+				goto unlock;
 			param = &esco_param_cvsd[conn->attempt - 1];
 		} else {
 			if (conn->attempt > ARRAY_SIZE(sco_param_cvsd))
-				return -EINVAL;
+				goto unlock;
 			param = &sco_param_cvsd[conn->attempt - 1];
 		}
 		cp.tx_coding_format.id = 2;
@@ -386,9 +388,11 @@ static int hci_enhanced_setup_sync(struct hci_dev *hdev, void *data)
 		cp.out_transport_unit_size = 16;
 		break;
 	default:
-		return -EINVAL;
+		goto unlock;
 	}
 
+	hci_dev_unlock(hdev);
+
 	cp.retrans_effort = param->retrans_effort;
 	cp.pkt_type = __cpu_to_le16(param->pkt_type);
 	cp.max_latency = __cpu_to_le16(param->max_latency);
@@ -397,6 +401,10 @@ static int hci_enhanced_setup_sync(struct hci_dev *hdev, void *data)
 		return -EIO;
 
 	return 0;
+
+unlock:
+	hci_dev_unlock(hdev);
+	return -EINVAL;
 }
 
 static bool hci_setup_sync_conn(struct hci_conn *conn, __u16 handle)
-- 
2.43.0