From f59fcad27535c7efd8017e084cf215ece392a85f Mon Sep 17 00:00:00 2001

From: nick black <dankamongmen@gmail.com>

Date: Mon, 30 Aug 2021 04:56:15 -0400

Subject: [PATCH] console: consume APC, DM, DCS

Git-commit: 3a2b2eb55681158d3e3ef464fbf47574cf0c517c

Patch-mainline: v5.15-rc1

References: stable-5.14.8

commit 3a2b2eb55681158d3e3ef464fbf47574cf0c517c upstream.

The Linux console's VT102 implementation already consumes OSC

("Operating System Command") sequences, probably because that's how

palette changes are transmitted.

In addition to OSC, there are three other major clases of ANSI control

Strings: APC ("Application Program Command"), PM ("Privacy Message"),

and DCS ("Device Control String").  They are handled similarly to OSC in

terms of termination.

Source: vt100.net

Add three new enumerated states, one for each of these types.  All three

are handled the same way right now--they simply consume input until

terminated.  I hope to expand upon this firmament in the future.  Add

new predicate ansi_control_string(), returning true for any of these

states.  Replace explicit checks against ESosc with calls to this

function.  Transition to these states appropriately from the escape

initiation (ESesc) state.

This was motivated by the following Notcurses bugs:

 https://github.com/dankamongmen/notcurses/issues/2050

 https://github.com/dankamongmen/notcurses/issues/1828

 https://github.com/dankamongmen/notcurses/issues/2069

where standard VT sequences are not consumed by the Linux console.  It's

not necessary that the Linux console *support* these sequences, but it

ought *consume* these well-specified classes of sequences.

Tested by sending a variety of escape sequences to the console, and

verifying that they still worked, or were now properly consumed.

Verified that the escapes were properly terminated at a generic level.

Verified that the Notcurses tools continued to show expected output on

the Linux console, except now without escape bleedthrough.

Link: https://lore.kernel.org/lkml/YSydL0q8iaUfkphg@schwarzgerat.orthanc/

Signed-off-by: nick black <dankamongmen@gmail.com>

Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Cc: Jiri Slaby <jirislaby@kernel.org>

Cc: Tetsuo Handa <penguin-kernel@i-love.sakura.ne.jp>

Cc: Daniel Vetter <daniel.vetter@ffwll.ch>

Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Acked-by: Takashi Iwai <tiwai@suse.de>

---

 drivers/tty/vt/vt.c | 31 +++++++++++++++++++++++++++----

 1 file changed, 27 insertions(+), 4 deletions(-)

diff --git a/drivers/tty/vt/vt.c b/drivers/tty/vt/vt.c

index ef981d3b7bb4..cb72393f92d3 100644

--- a/drivers/tty/vt/vt.c

+++ b/drivers/tty/vt/vt.c

@@ -2059,7 +2059,7 @@ static void restore_cur(struct vc_data *vc)

 enum { ESnormal, ESesc, ESsquare, ESgetpars, ESfunckey,

 	EShash, ESsetG0, ESsetG1, ESpercent, EScsiignore, ESnonstd,

-	ESpalette, ESosc };

+	ESpalette, ESosc, ESapc, ESpm, ESdcs };

 /* console_lock is held (except via vc_init()) */

 static void reset_terminal(struct vc_data *vc, int do_clear)

@@ -2133,20 +2133,28 @@ static void vc_setGx(struct vc_data *vc, unsigned int which, int c)

 		vc->vc_translate = set_translate(*charset, vc);

 }

+/* is this state an ANSI control string? */

+static bool ansi_control_string(unsigned int state)

+{

+	if (state == ESosc || state == ESapc || state == ESpm || state == ESdcs)

+		return true;

+	return false;

+}

+

 /* console_lock is held */

 static void do_con_trol(struct tty_struct *tty, struct vc_data *vc, int c)

 {

 	/*

 	 *  Control characters can be used in the _middle_

-	 *  of an escape sequence.

+	 *  of an escape sequence, aside from ANSI control strings.

 	 */

-	if (vc->vc_state == ESosc && c>=8 && c<=13) /* ... except for OSC */

+	if (ansi_control_string(vc->vc_state) && c >= 8 && c <= 13)

 		return;

 	switch (c) {

 	case 0:

 		return;

 	case 7:

-		if (vc->vc_state == ESosc)

+		if (ansi_control_string(vc->vc_state))

 			vc->vc_state = ESnormal;

 		else if (vc->vc_bell_duration)

 			kd_mksound(vc->vc_bell_pitch, vc->vc_bell_duration);

@@ -2207,6 +2215,12 @@ static void do_con_trol(struct tty_struct *tty, struct vc_data *vc, int c)

 		case ']':

 			vc->vc_state = ESnonstd;

 			return;

+		case '_':

+			vc->vc_state = ESapc;

+			return;

+		case '^':

+			vc->vc_state = ESpm;

+			return;

 		case '%':

 			vc->vc_state = ESpercent;

 			return;

@@ -2224,6 +2238,9 @@ static void do_con_trol(struct tty_struct *tty, struct vc_data *vc, int c)

 			if (vc->state.x < VC_TABSTOPS_COUNT)

 				set_bit(vc->state.x, vc->vc_tab_stop);

 			return;

+		case 'P':

+			vc->vc_state = ESdcs;

+			return;

 		case 'Z':

 			respond_ID(tty);

 			return;

@@ -2520,8 +2537,14 @@ static void do_con_trol(struct tty_struct *tty, struct vc_data *vc, int c)

 		vc_setGx(vc, 1, c);

 		vc->vc_state = ESnormal;

 		return;

+	case ESapc:

+		return;

 	case ESosc:

 		return;

+	case ESpm:

+		return;

+	case ESdcs:

+		return;

 	default:

 		vc->vc_state = ESnormal;

 	}

-- 

2.26.2