linux-kernel - Re: [PATCH v2 RESEND] tty/n_gsm.c: fix a memory leak when gsmtty is removed

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Message-ID: <551519FC.5030809@suse.cz>
Date:	Fri, 27 Mar 2015 09:51:08 +0100
From:	Jiri Slaby <jslaby@...e.cz>
To:	Pan Xinhui <xinhuix.pan@...el.com>, gregkh@...uxfoundation.org,
	linux-kernel@...r.kernel.org
CC:	yanmin_zhang@...ux.intel.com, mnipxh@...il.com
Subject: Re: [PATCH v2 RESEND] tty/n_gsm.c: fix a memory leak when gsmtty
 is removed

On 03/28/2015, 03:42 AM, Pan Xinhui wrote:
> when gsmtty_remove put dlci, it will cause memory leak if dlci->port's
> refcount is zero.
> So we do the cleanup work in .cleanup callback instead.
> 
> dlci will be last put in two call chains.
> 1) gsmld_close -> gsm_cleanup_mux -> gsm_dlci_release -> dlci_put
> 2) gsmld_remove -> dlci_put
> so there is a race. the memory leak depends on the race.
> 
> In call chain 2. we hit the memory leak. below comment tells.
> 
> release_tty -> tty_driver_remove_tty -> gsmtty_remove -> dlci_put ->
> tty_port_destructor (WARN_ON(port->itty) and return directly)
>                         |
>                tty->port->itty = NULL;
>                         |
>                tty_kref_put ---> release_one_tty -> gsmtty_cleanup
> (added by our patch)
> 
> So our patch fix the memory leak by doing the cleanup work after tty
> core did.
> 
> Signed-off-by: Pan Xinhui <xinhuix.pan@...el.com>

Fixes: dfabf7ffa30585
Acked-by: Jiri Slaby <jslaby@...e.cz>

> ---
> Changes in v2:
>  Don't use schedule_work to put dlci. Replace .remove with .cleanup
> callback.
> 
>  drivers/tty/n_gsm.c | 5 ++---
>  1 file changed, 2 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/tty/n_gsm.c b/drivers/tty/n_gsm.c
> index c434376..bce16e4 100644
> --- a/drivers/tty/n_gsm.c
> +++ b/drivers/tty/n_gsm.c
> @@ -3170,7 +3170,7 @@ static int gsmtty_break_ctl(struct tty_struct
> *tty, int state)
>      return gsmtty_modem_update(dlci, encode);
>  }
>  
> -static void gsmtty_remove(struct tty_driver *driver, struct tty_struct
> *tty)
> +static void gsmtty_cleanup(struct tty_struct *tty)
>  {
>      struct gsm_dlci *dlci = tty->driver_data;
>      struct gsm_mux *gsm = dlci->gsm;
> @@ -3178,7 +3178,6 @@ static void gsmtty_remove(struct tty_driver
> *driver, struct tty_struct *tty)
>      dlci_put(dlci);
>      dlci_put(gsm->dlci[0]);
>      mux_put(gsm);
> -    driver->ttys[tty->index] = NULL;
>  }
>  
>  /* Virtual ttys for the demux */
> @@ -3199,7 +3198,7 @@ static const struct tty_operations gsmtty_ops = {
>      .tiocmget        = gsmtty_tiocmget,
>      .tiocmset        = gsmtty_tiocmset,
>      .break_ctl        = gsmtty_break_ctl,
> -    .remove            = gsmtty_remove,
> +    .cleanup        = gsmtty_cleanup,
>  };
>  
>  


-- 
js
suse labs
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