Re: [PATCH] vt: detect and ignore OSC codes.

Greg Kroah-Hartman
2014-02-18T18:43:07Z

On Sun, Feb 16, 2014 at 03:37:59AM +0100, Adam Borowski wrote:
> On Thu, Feb 13, 2014 at 10:39:12AM -0800, Greg Kroah-Hartman wrote:
> > On Wed, Jan 15, 2014 at 07:21:04AM +0100, Adam Borowski wrote:
> > > These can be used to send commands consisting of an arbitrary string to the
> > > terminal, most often used to set a terminal's window title or to redefine
> > > the colour palette. Our console doesn't use OSC, unlike everything else,
> > > which can lead to junk being displayed if a process sends such a code
> > > unconditionally.
> > >
> > > Not following Ecma-48, this commit recognizes 7-bit forms (ESC ] ... 0x07,
> > > ESC ] .. ESC \) but not 8-bit (0x9D ... 0x9C).
> > >
> > > Signed-off-by: Adam Borowski <kilobyte@angband.pl>
> >
> > Where is this documented?
>
> It's a mix of Ecma-48 and undocumented practice. Ecma-48 says:
>
> # 8.3.89
> # OSC - OPERATING SYSTEM COMMAND
> # Notation: (C1)
> # Representation: 0x9D or ESC 0x5D (])
> #
> # OSC is used as the opening delimiter of a control string for operating
> # system use. The command string following may consist of a sequence of
> # bit combinations in the range 0x08 to 0x0D and 0x20 to 0x7E. The
> # control string is closed by the terminating delimiter STRING TERMINATOR
> # (ST). The interpretation of the command string depends on the relevant
> # operating system.
>
> # 8.3.143
> # ST - STRING TERMINATOR
> # Notation: (C1)
> # Representation: 0x9C or ESC 0x5C (\)
> #
> # ST is used as the closing delimiter of a control string opened by
> # APPLICATION PROGRAM COMMAND (APC), DEVICE CONTROL STRING (DCS),
> # OPERATING SYSTEM COMMAND (OSC), PRIVACY MESSAGE (PM), or START OF STRING
> # (SOS).
>
> ... which doesn't define the behaviour for characters 0x00..0x07, 0x0E..0x1F
> or 0x7F..0xFF. Somehow, using 0x07 for termination became a widespread
> idiom, used more often than proper ESC \. For this reason, implementations
> I know all recognize 0x07 as a terminator. The behaviour for other
> characters differs, ie, is truly undefined.
>
> As, unlike what Ecma-48 says, using 8-bit characters in a window title is a
> reasonable thing to do, I'd allow 0x80..0xFF as non-terminators. I have no
> idea what to do with remaining control characters: the current patch allows
> them to be interpreted, as it's usually the case for control characters
> inside terminal codes. I did not research other implementation here.
>
> I did not recognize 0x9C as ST for two reasons: 1. it'd break non-ASCII
> characters that happen to include this byte, and 2. Linux already fails to
> recognize 8-bit control codes (with one exception: 0x9B stands for ESC [).
>
>
> Should I put the above explanation somewhere? As a comment? In the commit
> message? Or does it need to be elaborated even further?

In the commit message would be best.

> > > @@ -2023,6 +2029,8 @@ static void do_con_trol(struct tty_struct *tty, struct vc_data *vc, int c)
> > > return;
> > > default:
> > > vc->vc_state = ESnormal;
> > > + case ESosc:
> > > + return;
> >
> > Why below the default: case?
>
> Just to shave a line and a return statement. From your objection, I guess
> this goes against the coding standards, right?

Yes it does.