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n_tty: signal and flush atomically

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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 d2b6f44779 ("n_tty: Fix signal handling flushes")
Reported-by: Filipe Brandenburger <filbranden@google.com>
Signed-off-by: Peter Hurley <peter@hurleysoftware.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Peter Hurley 2015-06-27 09:21:32 -04:00 committed by Greg Kroah-Hartman
parent 52721d9d33
commit 3b19e03229
1 changed files with 13 additions and 3 deletions
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16
drivers/tty/n_tty.c
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@ -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;