From: Thadeu Lima de Souza Cascardo <cascardo@canonical.com> mainline inclusion from mainline-v5.14-rc1 commit 3cfdf8fcaafa62a4123f92eb0f4a72650da3a479 category: bugfix bugzilla: NA CVE: CVE-2021-34981 ------------------------------------------------- When cmtp_attach_device fails, cmtp_add_connection returns the error value which leads to the caller to doing fput through sockfd_put. But cmtp_session kthread, which is stopped in this path will also call fput, leading to a potential refcount underflow or a use-after-free. Add a refcount before we signal the kthread to stop. The kthread will try to grab the cmtp_session_sem mutex before doing the fput, which is held when get_file is called, so there should be no races there. Reported-by: Ryota Shiga Signed-off-by: Thadeu Lima de Souza Cascardo <cascardo@canonical.com> Signed-off-by: Marcel Holtmann <marcel@holtmann.org> Signed-off-by: Yang Yingliang <yangyingliang@huawei.com> Reviewed-by: weiyang wang <wangweiyang2@huawei.com> Signed-off-by: Yang Yingliang <yangyingliang@huawei.com> --- net/bluetooth/cmtp/core.c | 5 +++++ 1 file changed, 5 insertions(+) diff --git a/net/bluetooth/cmtp/core.c b/net/bluetooth/cmtp/core.c index 7f26a5a19ff6d..9873684a9d8ff 100644 --- a/net/bluetooth/cmtp/core.c +++ b/net/bluetooth/cmtp/core.c @@ -391,6 +391,11 @@ int cmtp_add_connection(struct cmtp_connadd_req *req, struct socket *sock) if (!(session->flags & BIT(CMTP_LOOPBACK))) { err = cmtp_attach_device(session); if (err < 0) { + /* Caller will call fput in case of failure, and so + * will cmtp_session kthread. + */ + get_file(session->sock->file); + atomic_inc(&session->terminate); wake_up_interruptible(sk_sleep(session->sock->sk)); up_write(&cmtp_session_sem); -- 2.25.1