From 752a6c9596dd25efd6978a73ff21f3b592668f4a Mon Sep 17 00:00:00 2001 From: Shaurya Rane Date: Thu, 6 Nov 2025 23:50:16 +0530 Subject: [PATCH] Bluetooth: L2CAP: Fix use-after-free in l2cap_unregister_user After commit ab4eedb790ca ("Bluetooth: L2CAP: Fix corrupted list in hci_chan_del"), l2cap_conn_del() uses conn->lock to protect access to conn->users. However, l2cap_register_user() and l2cap_unregister_user() don't use conn->lock, creating a race condition where these functions can access conn->users and conn->hchan concurrently with l2cap_conn_del(). This can lead to use-after-free and list corruption bugs, as reported by syzbot. Fix this by changing l2cap_register_user() and l2cap_unregister_user() to use conn->lock instead of hci_dev_lock(), ensuring consistent locking for the l2cap_conn structure. Reported-by: syzbot+14b6d57fb728e27ce23c@syzkaller.appspotmail.com Closes: https://syzkaller.appspot.com/bug?extid=14b6d57fb728e27ce23c Fixes: ab4eedb790ca ("Bluetooth: L2CAP: Fix corrupted list in hci_chan_del") Signed-off-by: Shaurya Rane Signed-off-by: Luiz Augusto von Dentz --- net/bluetooth/l2cap_core.c | 20 ++++++++------------ 1 file changed, 8 insertions(+), 12 deletions(-) diff --git a/net/bluetooth/l2cap_core.c b/net/bluetooth/l2cap_core.c index 0f400051f093..780136e18aae 100644 --- a/net/bluetooth/l2cap_core.c +++ b/net/bluetooth/l2cap_core.c @@ -1678,17 +1678,15 @@ static void l2cap_info_timeout(struct work_struct *work) int l2cap_register_user(struct l2cap_conn *conn, struct l2cap_user *user) { - struct hci_dev *hdev = conn->hcon->hdev; int ret; /* We need to check whether l2cap_conn is registered. If it is not, we - * must not register the l2cap_user. l2cap_conn_del() is unregisters - * l2cap_conn objects, but doesn't provide its own locking. Instead, it - * relies on the parent hci_conn object to be locked. This itself relies - * on the hci_dev object to be locked. So we must lock the hci device - * here, too. */ + * must not register the l2cap_user. l2cap_conn_del() unregisters + * l2cap_conn objects under conn->lock, and we use the same lock here + * to protect access to conn->users and conn->hchan. + */ - hci_dev_lock(hdev); + mutex_lock(&conn->lock); if (!list_empty(&user->list)) { ret = -EINVAL; @@ -1709,16 +1707,14 @@ int l2cap_register_user(struct l2cap_conn *conn, struct l2cap_user *user) ret = 0; out_unlock: - hci_dev_unlock(hdev); + mutex_unlock(&conn->lock); return ret; } EXPORT_SYMBOL(l2cap_register_user); void l2cap_unregister_user(struct l2cap_conn *conn, struct l2cap_user *user) { - struct hci_dev *hdev = conn->hcon->hdev; - - hci_dev_lock(hdev); + mutex_lock(&conn->lock); if (list_empty(&user->list)) goto out_unlock; @@ -1727,7 +1723,7 @@ void l2cap_unregister_user(struct l2cap_conn *conn, struct l2cap_user *user) user->remove(conn, user); out_unlock: - hci_dev_unlock(hdev); + mutex_unlock(&conn->lock); } EXPORT_SYMBOL(l2cap_unregister_user);