From 9b851b09b392da68bd715601f10a5adb2d8d19b8 Mon Sep 17 00:00:00 2001 From: Krystian Kaniewski Date: Fri, 4 Sep 2026 12:24:22 +0000 Subject: [PATCH] Bluetooth: hci_sysfs: Fix NULL pointer dereference in device_del() A NULL pointer dereference in klist_put() occurs when a child device (such as a BNEP network device in bnep_session) is concurrently being unregistered while hci_conn_del_sysfs() reparents child devices. This is caused by a race condition between hci_conn_del_sysfs() and concurrent child device unregistration (e.g. bnep_session calling unregister_netdev()). During device unregistration, device_del() snapshots a non-NULL parent pointer. Concurrently, hci_conn_del_sysfs() finds the child device using device_find_any_child() and calls device_move() to reparent it to NULL, which removes the node from its parent's klist and clears knode_parent. Subsequently, device_del() calls klist_del(&dev->p->knode_parent) using the stale parent snapshot, causing klist_put() to dereference knode_klist(n)->put on an already removed node, resulting in a NULL pointer dereference. This race was introduced by commit 27aabf27fd01 ("Bluetooth: fix use-after-free in device_for_each_child()"), which replaced device_find_child(..., __match_tty) with device_find_any_child() in hci_conn_del_sysfs(). That change was intended to avoid a use-after-free where conn->dev outlived its parent hdev->dev when child devices held references to conn->dev, because conn->dev only held a reference to hdev->dev while registered in sysfs. Fix the issue properly by taking an explicit reference to the parent device with get_device(&hdev->dev) in hci_conn_init_sysfs() and dropping it with put_device(parent) in bt_link_release() when the conn device is freed. This ensures that hdev->dev remains valid for the entire lifecycle of conn->dev, resolving the underlying use-after-free. With the parent reference held properly, restore the __match_tty filter in hci_conn_del_sysfs() so that device_move() is only invoked on persistent RFCOMM TTY devices as originally intended, eliminating the race condition with unregistering network devices. Fixes: 27aabf27fd01 ("Bluetooth: fix use-after-free in device_for_each_child()") Assisted-by: Gemini:gemini-3.7-flash syzbot Reported-by: syzbot+6df45dd3d03e1a9aca96@syzkaller.appspotmail.com Closes: https://syzkaller.appspot.com/bug?extid=6df45dd3d03e1a9aca96 Link: https://syzkaller.appspot.com/ai_job?id=f1c0e740-db21-40af-a9ff-84db0fd8b8bd Signed-off-by: Krystian Kaniewski Signed-off-by: Luiz Augusto von Dentz --- net/bluetooth/hci_sysfs.c | 17 +++++++++++++++-- 1 file changed, 15 insertions(+), 2 deletions(-) diff --git a/net/bluetooth/hci_sysfs.c b/net/bluetooth/hci_sysfs.c index 8957ce7c21b7..c2065abf753e 100644 --- a/net/bluetooth/hci_sysfs.c +++ b/net/bluetooth/hci_sysfs.c @@ -13,7 +13,10 @@ static const struct class bt_class = { static void bt_link_release(struct device *dev) { struct hci_conn *conn = to_hci_conn(dev); + struct device *parent = dev->parent; + kfree(conn); + put_device(parent); } static const struct device_type bt_link = { @@ -21,6 +24,16 @@ static const struct device_type bt_link = { .release = bt_link_release, }; +/* + * The rfcomm tty device will possibly retain even when conn + * is down, and sysfs doesn't support move zombie device, + * so we should move the device before conn device is destroyed. + */ +static int __match_tty(struct device *dev, const void *data) +{ + return !strncmp(dev_name(dev), "rfcomm", 6); +} + void hci_conn_init_sysfs(struct hci_conn *conn) { struct hci_dev *hdev = conn->hdev; @@ -29,7 +42,7 @@ void hci_conn_init_sysfs(struct hci_conn *conn) conn->dev.type = &bt_link; conn->dev.class = &bt_class; - conn->dev.parent = &hdev->dev; + conn->dev.parent = get_device(&hdev->dev); device_initialize(&conn->dev); } @@ -69,7 +82,7 @@ void hci_conn_del_sysfs(struct hci_conn *conn) while (1) { struct device *dev; - dev = device_find_any_child(&conn->dev); + dev = device_find_child(&conn->dev, NULL, __match_tty); if (!dev) break; device_move(dev, NULL, DPM_ORDER_DEV_LAST);