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 d2b6f44779d3 ("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>
diff --git a/drivers/tty/n_tty.c b/drivers/tty/n_tty.c
index c9c27f6..ee8bfac 100644
--- a/drivers/tty/n_tty.c
+++ b/drivers/tty/n_tty.c
@@ -1108,19 +1108,29 @@
* 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;