Re: tty_register_device NULL pointer dereference in 2.6.31-rc4

[Oliver Hartkopp <oliver@hartkopp.net>]

Dave Young wrote:
> On Sat, Jul 25, 2009 at 01:10:46PM +0100, Alan Cox wrote:
>>>> tty_register_device appears to have been called with a NULL pointer. Not
>>>> sure why however.
>>> if that is the pointer for the struct device, then that used to be fine
>>> in the past. Not all RFCOMM device have a parent when they are created.
>> The tty layer doesn't care about the struct device really. Nothing there
>> has changed. The NULL passed appears to be the driver argument.
> 
> Agree with you, because in rfcomm_init, rfcomm thread run before tty initilized, the following patch may fix the problem.
> oliver, could you verify it it fix your problem?

Hi Dave,

i get this problem really seldom on my Laptop and i did not manage to get a
reproducible Oops of that problem.

Anyway the code you are pointing to seems to have a problem and your added
error handling looks good to me - even if i don't know if the initializations
can be reordered in that way.

I'll try your patch, but it could take a *long* time to prove it right ;-)

Maybe Marcel and Alan can better prove it to be correct by code review.

Many thanks,
Oliver


> ---
> 
> rfcomm tty may be used before rfcomm_tty_driver initilized,
> 
> reporting in:
> http://marc.info/?l=linux-bluetooth&m=124404919324542&w=2
> 
> make 3 changes:
> 1. remove #ifdef in rfcomm/core.c,
> make it blank function when rfcomm tty not selected in rfcomm.h
> 
> 2. tune the rfcomm_init error patch to ensure
> tty driver initilized before any usage.
> 
> 3. remove __exit for rfcomm_cleanup_sockets
> because above change need call it in a __init function. 
> 
> 
> CC: Alan Cox <alan@lxorguk.ukuu.org.uk>
> Reported-by: Oliver Hartkopp <oliver@hartkopp.net>
> Signed-off-by: Dave Young <hidave.darkstar@gmail.com>
> --
> include/net/bluetooth/rfcomm.h |   13 ++++++++++++-
> net/bluetooth/rfcomm/core.c    |   31 +++++++++++++++++++++----------
> net/bluetooth/rfcomm/sock.c    |    2 +-
> 3 files changed, 34 insertions(+), 12 deletions(-)
> 
> --- linux-2.6.orig/include/net/bluetooth/rfcomm.h	2009-04-09 16:23:03.000000000 +0800
> +++ linux-2.6/include/net/bluetooth/rfcomm.h	2009-07-27 17:14:43.000000000 +0800
> @@ -355,7 +355,18 @@ struct rfcomm_dev_list_req {
>  };
>  
>  int  rfcomm_dev_ioctl(struct sock *sk, unsigned int cmd, void __user *arg);
> +
> +#ifdef CONFIG_BT_RFCOMM_TTY
>  int  rfcomm_init_ttys(void);
>  void rfcomm_cleanup_ttys(void);
> -
> +#else
> +static inline int rfcomm_init_ttys(void)
> +{
> +	return 0;
> +}
> +static inline int rfcomm_cleanup_ttys(void)
> +{
> +	return 0;
> +}
> +#endif
>  #endif /* __RFCOMM_H */
> --- linux-2.6.orig/net/bluetooth/rfcomm/core.c	2009-06-16 17:39:32.000000000 +0800
> +++ linux-2.6/net/bluetooth/rfcomm/core.c	2009-07-27 17:24:27.000000000 +0800
> @@ -2080,28 +2080,41 @@ static CLASS_ATTR(rfcomm_dlc, S_IRUGO, r
>  /* ---- Initialization ---- */
>  static int __init rfcomm_init(void)
>  {
> +	int ret;
> +
>  	l2cap_load();
>  
> +	ret = rfcomm_init_sockets();
> +	if (ret)
> +		goto out_sock;
> +
> +	ret = rfcomm_init_ttys();
> +	if (ret)
> +		goto out_tty;
> +
>  	hci_register_cb(&rfcomm_cb);
>  
>  	rfcomm_thread = kthread_run(rfcomm_run, NULL, "krfcommd");
>  	if (IS_ERR(rfcomm_thread)) {
> -		hci_unregister_cb(&rfcomm_cb);
> -		return PTR_ERR(rfcomm_thread);
> +		ret = PTR_ERR(rfcomm_thread);
> +		goto out_thread;
>  	}
>  
>  	if (class_create_file(bt_class, &class_attr_rfcomm_dlc) < 0)
>  		BT_ERR("Failed to create RFCOMM info file");
>  
> -	rfcomm_init_sockets();
> -
> -#ifdef CONFIG_BT_RFCOMM_TTY
> -	rfcomm_init_ttys();
> -#endif
> -
>  	BT_INFO("RFCOMM ver %s", VERSION);
>  
>  	return 0;
> +
> +out_thread:
> +	hci_unregister_cb(&rfcomm_cb);
> +out_tty:
> +	rfcomm_cleanup_ttys();
> +out_sock:
> +	rfcomm_cleanup_sockets();
> +
> +	return ret;
>  }
>  
>  static void __exit rfcomm_exit(void)
> @@ -2112,9 +2125,7 @@ static void __exit rfcomm_exit(void)
>  
>  	kthread_stop(rfcomm_thread);
>  
> -#ifdef CONFIG_BT_RFCOMM_TTY
>  	rfcomm_cleanup_ttys();
> -#endif
>  
>  	rfcomm_cleanup_sockets();
>  }
> --- linux-2.6.orig/net/bluetooth/rfcomm/sock.c	2009-04-09 16:23:04.000000000 +0800
> +++ linux-2.6/net/bluetooth/rfcomm/sock.c	2009-07-27 17:39:43.000000000 +0800
> @@ -1132,7 +1132,7 @@ error:
>  	return err;
>  }
>  
> -void __exit rfcomm_cleanup_sockets(void)
> +void rfcomm_cleanup_sockets(void)
>  {
>  	class_remove_file(bt_class, &class_attr_rfcomm);
>