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Bluetooth: cmtp: fix file refcount when cmtp_attach_device fails

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commit 8da3a0b87f4f1c3a3bbc4bfb78cf68476e97d183 upstream.

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: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Thadeu Lima de Souza Cascardo 2021-04-13 13:21:03 -03:00 • committed by Greg Kroah-Hartman
commit fe201316ac
1 changed files with 5 additions and 0 deletions
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5
net/bluetooth/cmtp/core.c
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@ -392,6 +392,11 @@ 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);