linux-kernel - Re: [PATCH 6/7] n_tty: Fix unsafe update of available buffer space

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Message-ID: <5148CA11.3010106@izyk.ru>
Date:	Wed, 20 Mar 2013 00:26:57 +0400
From:	Ilya Zykov <linux@...k.ru>
To:	Peter Hurley <peter@...leysoftware.com>
CC:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Jiri Slaby <jslaby@...e.cz>, linux-kernel@...r.kernel.org,
	linux-serial@...r.kernel.org
Subject: Re: [PATCH 6/7] n_tty: Fix unsafe update of available buffer space

On 19.03.2013 18:26, Peter Hurley wrote:
> receive_room is used to control the amount of data the flip
> buffer work can push to the read buffer. This update is unsafe:
> 
>   CPU 0                        |  CPU 1
>                                |
>                                | n_tty_read()
>                                |   n_tty_set_room()
>                                |     left = <calc of space>
> n_tty_receive_buf()            |
>   <push data to buffer>        |
>   n_tty_set_room()             |
>     left = <calc of space>     |
>     tty->receive_room = left   |
>                                |     tty->receive_room = left
> 
> receive_room is now updated with a stale calculation of the
> available buffer space, and the subsequent work loop will likely
> overwrite unread data in the input buffer.
> 

Sounds reasonable to me.
Thank you.
Ilya Zykov <linux@...k.ru>



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