linux-kernel - Re: [PATCH] tty: Fix unreasonable write toward closed pty.

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Message-ID: <20121221215505.6dab13ca@bob.linux.org.uk>
Date:	Fri, 21 Dec 2012 21:55:05 +0000
From:	Alan Cox <alan@...ux.intel.com>
To:	Ilya Zykov <ilya@...x.ru>
Cc:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Jiri Slaby <jslaby@...e.cz>,
	Peter Hurley <peter@...leysoftware.com>,
	Sasha Levin <levinsasha928@...il.com>,
	linux-serial@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] tty: Fix unreasonable write toward closed pty.

On Wed, 19 Dec 2012 22:59:19 +0400
Ilya Zykov <ilya@...x.ru> wrote:

> We should not write toward the closed pty. 
> Now it happens, if one side close last file descriptor,
> and other side in this moment write to it.
> It also prevents scheduling unnecessary work.
> 
> Signed-off-by: Ilya Zykov <ilya@...x.ru>
> ---
>  drivers/tty/pty.c |    2 ++
>  1 files changed, 2 insertions(+), 0 deletions(-)
> 
> diff --git a/drivers/tty/pty.c b/drivers/tty/pty.c
> index a82b399..1ce1362 100644
> --- a/drivers/tty/pty.c
> +++ b/drivers/tty/pty.c
> @@ -116,6 +116,8 @@ static int pty_space(struct tty_struct *to)
>  
>  static int pty_write(struct tty_struct *tty, const unsigned char
> *buf, int c) {
> +	if (test_bit(TTY_OTHER_CLOSED, &tty->flags))
> +		return -EIO;
>  	struct tty_struct *to = tty->link;

This

a) doesn't do anything in many cases because there is no lock to make
the test_bit meaningful

b) produces an obvious compiler warning

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