Re: [PATCH] tty: vt: selection: Add check for valid tiocl_selection values

From: Adam Borowski <kilobyte@angband.pl>
To: Jiri Slaby <jirislaby@kernel.org>
Cc: Helge Deller <deller@gmx.de>,
	Khalid Masum <khalid.masum.92@gmail.com>,
	syzbot <syzbot+14b0e8f3fd1612e35350@syzkaller.appspotmail.com>,
	dri-devel@lists.freedesktop.org, linux-fbdev@vger.kernel.org,
	linux-kernel@vger.kernel.org, syzkaller-bugs@googlegroups.com,
	Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Subject: Re: [PATCH] tty: vt: selection: Add check for valid tiocl_selection values
Date: Fri, 5 Aug 2022 13:13:15 +0200	[thread overview]
Message-ID: <Yuz7S18rHNbHCHly@angband.pl> (raw)
In-Reply-To: <2d4e82f9-e370-bb01-8656-fe0376c22a77@kernel.org>

On Thu, Aug 04, 2022 at 11:22:26AM +0200, Jiri Slaby wrote:
> On 04. 08. 22, 10:44, Helge Deller wrote:
> > On 8/4/22 09:15, Helge Deller wrote:
> > > On 8/4/22 07:47, Jiri Slaby wrote:
> > > > On 30. 07. 22, 20:49, Helge Deller wrote:
> > > > > The line and column numbers for the selection need to start at 1.
> > > > > Add the checks to prevent invalid input.

> > > > > --- a/drivers/tty/vt/selection.c
> > > > > +++ b/drivers/tty/vt/selection.c
> > > > > @@ -326,6 +326,9 @@ static int vc_selection(struct vc_data *vc, struct tiocl_selection *v,
> > > > > +    if (!v->xs || !v->ys || !v->xe || !v->ye)
> > > > > +        return -EINVAL;
> > > > 
> > > > Hmm, I'm not sure about this. It potentially breaks userspace (by
> > > > returning EINVAL now).

> We can still do a trial and revert it if something breaks... It's just that
> _noone_ knows with all this undocumented stuff ;).
> 
> But in fact, 0 currently means full row/column. Isn't it on purpose?
> 
> Today, we are out of luck, codesearch.debian.net gives no clue about users:
> https://codesearch.debian.net/search?q=%5CbTIOCL_SETSEL%5Cb&literal=0

That's because the macro is undocumented.

"man ioctl_console" says:
       TIOCLINUX, subcode=2
              Set selection.  argp points to a [...]

thus everyone writes it as a number.

You'd need to grep for TIOCLINUX; there's not that many references to
check...

Meow!
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