linux-kernel - Re: [PATCH v2] tty: Prevent hw state corruption in exclusive mode reopen

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Date:	Wed, 7 Jan 2015 16:55:01 -0600
From:	Shreyas Bethur <shreyas.bethur@...com>
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 v2] tty: Prevent hw state corruption in exclusive mode reopen

Peter Hurley <peter@...leysoftware.com> wrote on 12/30/2014 09:39:25 AM:

> From: Peter Hurley <peter@...leysoftware.com>
> To: Greg Kroah-Hartman <gregkh@...uxfoundation.org>, 
> Cc: Jiri Slaby <jslaby@...e.cz>, linux-kernel@...r.kernel.org, 
> linux-serial@...r.kernel.org, Shreyas Bethur 
> <shreyas.bethur@...com>, Peter Hurley <peter@...leysoftware.com>
> Date: 12/30/2014 09:39 AM
> Subject: [PATCH v2] tty: Prevent hw state corruption in exclusive mode 
reopen
> 
> Exclusive mode ttys (TTY_EXCLUSIVE) do not allow further reopens;
> fail the condition before associating the file pointer and calling
> the driver open() method.
> 
> Prevents DTR programming when the tty is already in exclusive mode.
> 
> Reported-by: Shreyas Bethur <shreyas.bethur@...com>
> Signed-off-by: Peter Hurley <peter@...leysoftware.com>
> ---
>  drivers/tty/tty_io.c | 7 +++----
>  1 file changed, 3 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/tty/tty_io.c b/drivers/tty/tty_io.c
> index 4f35b43..51f066a 100644
> --- a/drivers/tty/tty_io.c
> +++ b/drivers/tty/tty_io.c
> @@ -1464,6 +1464,9 @@ static int tty_reopen(struct tty_struct *tty)
>         driver->subtype == PTY_TYPE_MASTER)
>        return -EIO;
> 
> +   if (test_bit(TTY_EXCLUSIVE, &tty->flags) && !capable(CAP_SYS_ADMIN))
> +      return -EBUSY;
> +
>     tty->count++;
> 
>     WARN_ON(!tty->ldisc);
> @@ -2106,10 +2109,6 @@ retry_open:
>        retval = -ENODEV;
>     filp->f_flags = saved_flags;
> 
> -   if (!retval && test_bit(TTY_EXCLUSIVE, &tty->flags) &&
> -                  !capable(CAP_SYS_ADMIN))
> -      retval = -EBUSY;
> -
>     if (retval) {
>  #ifdef TTY_DEBUG_HANGUP
>        printk(KERN_DEBUG "%s: error %d in opening %s...\n", __func__,
> -- 
> 2.2.1
> 

Acked-by: Shreyas Bethur <shreyas.bethur@...com>

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