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Commit 3b19e032 authored by Peter Hurley's avatar Peter Hurley Committed by Greg Kroah-Hartman
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n_tty: signal and flush atomically 



When handling signalling char, claim the termios write lock before
signalling waiting readers and writers to prevent further i/o
before flushing the echo and output buffers. This prevents a
userspace signal handler which may output from racing the terminal
flush.

Reference: Bugzilla #99351 ("Output truncated in ssh session after...")
Fixes: commit d2b6f447 ("n_tty: Fix signal handling flushes")
Reported-by: default avatarFilipe Brandenburger <filbranden@google.com>
Signed-off-by: default avatarPeter Hurley <peter@hurleysoftware.com>
Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
parent 52721d9d

drivers/tty/n_tty.c

+13 −3
Original line number Diff line number Diff line
@@ -1108,19 +1108,29 @@ static void eraser(unsigned char c, struct tty_struct *tty) 
 *	Locking: ctrl_lock

 */



static void isig(int sig, struct tty_struct *tty)

static void __isig(int sig, struct tty_struct *tty)

{

	struct n_tty_data *ldata = tty->disc_data;

	struct pid *tty_pgrp = tty_get_pgrp(tty);

	if (tty_pgrp) {

		kill_pgrp(tty_pgrp, sig, 1);

		put_pid(tty_pgrp);

	}

}



	if (!L_NOFLSH(tty)) {

static void isig(int sig, struct tty_struct *tty)

{

	struct n_tty_data *ldata = tty->disc_data;



	if (L_NOFLSH(tty)) {

		/* signal only */

		__isig(sig, tty);



	} else { /* signal and flush */

		up_read(&tty->termios_rwsem);

		down_write(&tty->termios_rwsem);



		__isig(sig, tty);



		/* clear echo buffer */

		mutex_lock(&ldata->output_lock);

		ldata->echo_head = ldata->echo_tail = 0;