linux-kernel - Re: VT_PROCESS, VT_LOCKSWITCH capabilities

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Date:	Wed, 1 Aug 2007 15:19:00 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Frank Benkstein <frank@...kstein.net>
Cc:	linux-kernel@...r.kernel.org
Subject: Re: VT_PROCESS, VT_LOCKSWITCH capabilities

On Wed, 01 Aug 2007 04:44:32 +0200
Frank Benkstein <frank@...kstein.net> wrote:

> Frank Benkstein wrote:
> > I wonder why there are different permissions needed for VT_PROCESS
> > (access to the current virtual console) and VT_LOCKSWITCH
> > (CAP_SYS_TTY_CONFIG).
> 
> To be more direct:
> 
> require CAP_SYS_TTY_CONFIG for VT_SETMODE as its essentially the same as
> VT_LOCKSWITCH and said capability is already required there
> 
> diff --git a/drivers/char/vt_ioctl.c b/drivers/char/vt_ioctl.c
> index c6f6f42..7034a68 100644
> --- a/drivers/char/vt_ioctl.c
> +++ b/drivers/char/vt_ioctl.c
> @@ -662,7 +662,7 @@ int vt_ioctl(struct tty_struct *tty, struct file * file,
>         {
>                 struct vt_mode tmp;
> 
> -               if (!perm)
> +               if (!perm || !capable(CAP_SYS_TTY_CONFIG))
>                         return -EPERM;
>                 if (copy_from_user(&tmp, up, sizeof(struct vt_mode)))
>                         return -EFAULT;
> 

There's a good risk of breaking stuff with this change.  A quick peek
through http://www.google.com/codesearch shows that.

We need good reasons for making that change, and for handling the
subsequent fallout, getting shouted at by aggrieved users, etc.

It's tricky.
-
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