Re: [PATCH 1/2] tty: n_gsm: fix race condition in status line change on dead connections

[Greg KH <gregkh@linuxfoundation.org>]

On Thu, Oct 26, 2023 at 07:58:43AM +0200, D. Starke wrote:
> From: Daniel Starke <daniel.starke@siemens.com>
> 
> 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.
> 
> Fixes: c568f7086c6e ("tty: n_gsm: fix missing timer to handle stalled links")
> Signed-off-by: Daniel Starke <daniel.starke@siemens.com>
> ---
>  drivers/tty/n_gsm.c | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/drivers/tty/n_gsm.c b/drivers/tty/n_gsm.c
> index 1f3aba607cd5..0ee7531c9201 100644
> --- a/drivers/tty/n_gsm.c
> +++ b/drivers/tty/n_gsm.c
> @@ -4108,6 +4108,8 @@ static int gsm_modem_upd_via_msc(struct gsm_dlci *dlci, u8 brk)
>  
>  static int gsm_modem_update(struct gsm_dlci *dlci, u8 brk)
>  {
> +	if (dlci->gsm->dead)
> +		return -EL2HLT;
>  	if (dlci->adaption == 2) {
>  		/* Send convergence layer type 2 empty data frame. */
>  		gsm_modem_upd_via_data(dlci, brk);
> -- 
> 2.34.1
> 

Hi,

This is the friendly patch-bot of Greg Kroah-Hartman.  You have sent him
a patch that has triggered this response.  He used to manually respond
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