CVE-2023-52872

In the Linux kernel, the following vulnerability has been resolved: tty:
n_gsm: fix race condition in status line change on dead connections
gsm_cleanup_mux() cleans up the gsm by closing all DLCIs, stopping all
timers, removing the virtual tty devices and clearing the data queues. This
procedure, however, may cause subsequent changes of the virtual modem
status lines of a DLCI. More data is being added the outgoing data queue
and the deleted kick timer is restarted to handle this. At this point many
resources have already been removed by the cleanup procedure. Thus, a
kernel panic occurs. Fix this by proving in gsm_modem_update() that the
cleanup procedure has not been started and the mux is still alive. Note
that writing to a virtual tty is already protected by checks against the
DLCI specific connection state.