In the Linux kernel, the following vulnerability has been resolved: Bluetooth: RFCOMM: hold listener socket in rfcomm_connect_ind() rfcomm

In the Linux kernel, the following vulnerability has been resolved:

Bluetooth: RFCOMM: hold listener socket in rfcomm_connect_ind()

rfcomm_get_sock_by_channel() scans rfcomm_sk_list under the list lock,
but returns the selected listener after dropping that lock without
taking a reference. rfcomm_connect_ind() then locks the listener,
queues a child socket on it, and may notify it after unlocking it.

The buggy scenario involves two paths, with each column showing the
order within that path:

rfcomm_connect_ind(): listener close:

1. Find parent in 1. close() enters
   rfcomm_get_sock_by_channel() rfcomm_sock_release().
2. Drop rfcomm_sk_list.lock 2. rfcomm_sock_shutdown()
   without pinning parent. closes the listener.
3. Call lock_sock(parent) and 3. rfcomm_sock_kill()
   bt_accept_enqueue(parent, unlinks and puts parent.
   sk, true).
4. Read parent flags and may 4. parent can be freed.
   call sk_state_change().

If close wins the race, parent can be freed before
rfcomm_connect_ind() reaches lock_sock(), bt_accept_enqueue(), or the
deferred-setup callback.

Take a reference on the listener before leaving rfcomm_sk_list.lock.
After lock_sock() succeeds, recheck that it is still in BT_LISTEN
before queueing a child, cache the deferred-setup bit while the parent
is locked, and drop the reference after the last parent use.

KASAN reported a slab-use-after-free in lock_sock_nested() from
rfcomm_connect_ind(), with the freeing stack going through
rfcomm_sock_kill() and rfcomm_sock_release().