linux-kernel - Re: [PATCH] tty: Add missing lock in n_tty

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Date:	Wed, 15 May 2013 17:03:17 +0200
From:	Jiri Slaby <jslaby@...e.cz>
To:	Joerg Roedel <joro@...tes.org>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
CC:	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] tty: Add missing lock in n_tty_write()

On 05/15/2013 12:56 PM, Joerg Roedel wrote:
> The call of the tty->ops->write callback is protected by
> output_lock in all other places I looked at. So it seems the
> lock in this code-branch is missing, so take the output_lock
> there too.
> 
> Cc: stable@...r.kernel.org
> Signed-off-by: Joerg Roedel <joro@...tes.org>
> ---
>  drivers/tty/n_tty.c |    5 +++++
>  1 file changed, 5 insertions(+)
> 
> diff --git a/drivers/tty/n_tty.c b/drivers/tty/n_tty.c
> index d655416..ffb94a4 100644
> --- a/drivers/tty/n_tty.c
> +++ b/drivers/tty/n_tty.c
> @@ -2058,10 +2058,14 @@ static ssize_t n_tty_write(struct tty_struct *tty, struct file *file,
>  			if (tty->ops->flush_chars)
>  				tty->ops->flush_chars(tty);
>  		} else {
> +			struct n_tty_data *l = tty->disc_data;
> +
> +			mutex_lock(&l->output_lock);
>  			while (nr > 0) {
>  				c = tty->ops->write(tty, b, nr);
>  				if (c < 0) {
>  					retval = c;
> +					mutex_unlock(&l->output_lock);
>  					goto break_out;
>  				}
>  				if (!c)
> @@ -2069,6 +2073,7 @@ static ssize_t n_tty_write(struct tty_struct *tty, struct file *file,
>  				b += c;
>  				nr -= c;
>  			}
> +			mutex_unlock(&l->output_lock);
>  		}
>  		if (!nr)
>  			break;
> 

Are you fixing any bug here? output_lock does not protect
tty->ops->write on the other places, not tty->ops->write.

thanks,
-- 
js
suse labs
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