[PATCH v4] Bluetooth: hci_conn: fix potential UAF in create_big_sync

[David Carlier <devnexen@gmail.com>]

Add hci_conn_valid() check in create_big_sync() to detect stale
connections before proceeding with BIG creation. Handle the
resulting -ECANCELED in create_big_complete() and re-validate the
connection under hci_dev_lock() before dereferencing, matching the
pattern used by create_le_conn_complete() and create_pa_complete().

Keep the hci_conn object alive across the async boundary by taking
a reference via hci_conn_get() when queueing create_big_sync(), and
dropping it in the completion callback. The refcount and the lock
are complementary: the refcount keeps the object allocated, while
hci_dev_lock() serializes hci_conn_hash_del()'s list_del_rcu() on
hdev->conn_hash, as required by hci_conn_del().

hci_conn_put() is called outside hci_dev_unlock() so the final put
(which resolves to kfree() via bt_link_release) does not run under
hdev->lock, though the release path would be safe either way.

Without this, create_big_complete() would unconditionally
dereference the conn pointer on error, causing a use-after-free
via hci_connect_cfm() and hci_conn_del().

Fixes: eca0ae4aea66 ("Bluetooth: Add initial implementation of BIS connections")
Cc: stable@vger.kernel.org
Co-developed-by: Luiz Augusto von Dentz <luiz.von.dentz@intel.com>
Signed-off-by: Luiz Augusto von Dentz <luiz.von.dentz@intel.com>
Signed-off-by: David Carlier <devnexen@gmail.com>
---

v3 -> v4: combine v2's hci_dev_lock() wrapping in
  create_big_complete() with v3's refcount. hci_conn_del() now runs
  under hdev->lock as required by hci_conn_hash_del()'s
  list_del_rcu() on hdev->conn_hash (Pauli Virtanen review).
  hci_conn_put() is placed outside hci_dev_unlock() via a two-label
  unlock/done pattern so the final put (which resolves to kfree()
  via bt_link_release) does not nest under hdev->lock.
v2 -> v3 (Luiz): keep object alive across the async boundary via
  hci_conn_get() at the queue site and hci_conn_put() in the
  completion callback.
v1 -> v2: handle -ECANCELED and validate conn under hci_dev_lock()
  in create_big_complete().
v3: https://lore.kernel.org/r/20260410201343.229470-1-luiz.dentz@gmail.com
v1: https://lore.kernel.org/r/20260408155638.95927-1-devnexen@gmail.com
 net/bluetooth/hci_conn.c | 19 ++++++++++++++++++-
 1 file changed, 18 insertions(+), 1 deletion(-)

diff --git a/net/bluetooth/hci_conn.c b/net/bluetooth/hci_conn.c
index 11d3ad8d2551..9fa6901aae9f 100644
--- a/net/bluetooth/hci_conn.c
+++ b/net/bluetooth/hci_conn.c
@@ -2130,6 +2130,9 @@ static int create_big_sync(struct hci_dev *hdev, void *data)
 	u32 flags = 0;
 	int err;
 
+	if (!hci_conn_valid(hdev, conn))
+		return -ECANCELED;
+
 	if (qos->bcast.out.phys == BIT(1))
 		flags |= MGMT_ADV_FLAG_SEC_2M;
 
@@ -2204,11 +2207,24 @@ static void create_big_complete(struct hci_dev *hdev, void *data, int err)
 
 	bt_dev_dbg(hdev, "conn %p", conn);
 
+	if (err == -ECANCELED)
+		goto done;
+
+	hci_dev_lock(hdev);
+
+	if (!hci_conn_valid(hdev, conn))
+		goto unlock;
+
 	if (err) {
 		bt_dev_err(hdev, "Unable to create BIG: %d", err);
 		hci_connect_cfm(conn, err);
 		hci_conn_del(conn);
 	}
+
+unlock:
+	hci_dev_unlock(hdev);
+done:
+	hci_conn_put(conn);
 }
 
 struct hci_conn *hci_bind_bis(struct hci_dev *hdev, bdaddr_t *dst, __u8 sid,
@@ -2336,10 +2352,11 @@ struct hci_conn *hci_connect_bis(struct hci_dev *hdev, bdaddr_t *dst,
 				 BT_BOUND, &data);
 
 	/* Queue start periodic advertising and create BIG */
-	err = hci_cmd_sync_queue(hdev, create_big_sync, conn,
+	err = hci_cmd_sync_queue(hdev, create_big_sync, hci_conn_get(conn),
 				 create_big_complete);
 	if (err < 0) {
 		hci_conn_drop(conn);
+		hci_conn_put(conn);
 		return ERR_PTR(err);
 	}
 
-- 
2.53.0