From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id A51E644AB94; Fri, 4 Sep 2026 12:24:23 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1788524664; cv=none; b=IUkPb22lIdoHNbpuUjit9BDKKbODFgjmoWxswVgHKzKTPXJ95TXP1bP9+czp5PnxLtPrinLk0BhQ0hcx/y7Qfb3yv2BkWg0PNZURl2OisBU+gYsgSbKTRn66TodLpMbboi6dVfDs0kjQowJl7jRv4h4KB0Ne0x8tVi9SvhMkQ1w= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1788524664; c=relaxed/simple; bh=DvAvTw52vuzZFyP/uyq9o/hENAIlvcZrXJfVWLeVCRE=; h=From:To:Cc:Subject:Message-ID:MIME-Version:Content-Type:Date; b=k9n1ljPgYxgeGezUIK4Q+mAUmb+kCNa6ZGGTNz3btBtcBV4UPQ5suPQ+rMg+2+/izBXrqnuUMf7Io5PBXZ+H8jOsydnZVx9+QsI2ycHHvf0lO132UpCRiBWqdSFUjWxXZi+5ty9mAjH+LrEF6rXJWM912kV9pE3PlxlU5RfjWDc= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=e58QxgrK; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="e58QxgrK" Received: by smtp.kernel.org (Postfix) with UTF8SMTPSA id EBC531F00A3D; Fri, 4 Sep 2026 12:24:22 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1788524663; bh=JP3cmXMuLbeG7onVtl0q1r5cNTl2riebgD9aREchz8I=; h=From:To:Cc:Subject:Date; b=e58QxgrK469hrcKRpJsBP4VArHzV7DbpXS5D+OK0XdNTw5JNJqmqbKfO1jvUDudGp XF+Tbt2hx+bkwx02gm8rWGQtOtSHsTwuq0NcI1JwJHZOJ5BIs94MsIgDPLPJQTApZz zWEYaq2n3ntt6k/+2PpTfHGcIkxJAN9RG8z4trxrNZPF3TNd/VRUn6hk4UUob3OxiH 36fGwWXLnyOQ81fN2FjAlUy5G4GWvUq9FszJSfOze+qEDG9pVgdpimVej0rY0/btiK QyO0plM2Gah2D5+++V3M9sfqor96MLTkTKhVcOokAlOLI/FjDhsXLPVSOZc4dQL05Z 4ymA/hx0wVcfw== From: "syzbot" To: syzkaller-bugs@googlegroups.com, Krystian Kaniewski , , "Luiz Augusto von Dentz" , "Marcel Holtmann" , "Dmitry Antipov" Cc: linux-kernel@vger.kernel.org, syzbot@lists.linux.dev Subject: [PATCH] Bluetooth: hci_sysfs: Fix NULL pointer dereference in device_del() Message-ID: <388cbac3-b865-4843-bd65-c74059a5a459@mail.kernel.org> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Date: Fri, 4 Sep 2026 12:24:22 +0000 (UTC) From: Krystian Kaniewski 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 --- diff --git a/net/bluetooth/hci_sysfs.c b/net/bluetooth/hci_sysfs.c index 8957ce7c2..c2065abf7 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); base-commit: cee9395acd8043be0644b25c34bfa86623f2b935 -- See https://goo.gle/syzbot-ai-patches for information about AI-generated patches. The person who has signed off on the patch is responsible for addressing comments. syzbot engineers can be reached at syzkaller@googlegroups.com.