[PATCH 1/7] n_tty: Fix unsafe driver-side signals

Peter Hurley
2013-03-06T13:40:53Z

An ldisc reference is insufficient guarantee the foreground process
group is not in the process of being signalled from a hangup.

1) Reads of tty->pgrp must be locked with ctrl_lock
2) The group pid must be referenced for the duration of signalling.
Because the driver-side is not process-context, a pid reference
must be acquired.

Signed-off-by: Peter Hurley <peter@hurleysoftware.com>
---
drivers/tty/n_tty.c | 34 ++++++++++++++--------------------
1 file changed, 14 insertions(+), 20 deletions(-)

diff --git a/drivers/tty/n_tty.c b/drivers/tty/n_tty.c
index 66ce178..cd9ba3d 100644
--- a/drivers/tty/n_tty.c
+++ b/drivers/tty/n_tty.c
@@ -1038,23 +1038,19 @@ static void eraser(unsigned char c, struct tty_struct *tty)
* isig - handle the ISIG optio
* @sig: signal
* @tty: terminal
- * @flush: force flush
*
- * Called when a signal is being sent due to terminal input. This
- * may caus terminal flushing to take place according to the termios
- * settings and character used. Called from the driver receive_buf
- * path so serialized.
+ * Called when a signal is being sent due to terminal input.
+ * Called from the driver receive_buf path so serialized.
*
- * Locking: ctrl_lock, read_lock (both via flush buffer)
+ * Locking: ctrl_lock
*/

-static inline void isig(int sig, struct tty_struct *tty, int flush)
+static inline void isig(int sig, struct tty_struct *tty)
{
- if (tty->pgrp)
- kill_pgrp(tty->pgrp, sig, 1);
- if (flush || !L_NOFLSH(tty)) {
- n_tty_flush_buffer(tty);
- tty_driver_flush_buffer(tty);
+ struct pid *tty_pgrp = tty_get_pgrp(tty);
+ if (tty_pgrp) {
+ kill_pgrp(tty_pgrp, sig, 1);
+ put_pid(tty_pgrp);
}
}

@@ -1075,7 +1071,11 @@ static inline void n_tty_receive_break(struct tty_struct *tty)
if (I_IGNBRK(tty))
return;
if (I_BRKINT(tty)) {
- isig(SIGINT, tty, 1);
+ isig(SIGINT, tty);
+ if (!L_NOFLSH(tty)) {
+ n_tty_flush_buffer(tty);
+ tty_driver_flush_buffer(tty);
+ }
return;
}
if (I_PARMRK(tty)) {
@@ -1242,11 +1242,6 @@ static inline void n_tty_receive_char(struct tty_struct *tty, unsigned char c)
signal = SIGTSTP;
if (c == SUSP_CHAR(tty)) {
send_signal:
- /*
- * Note that we do not use isig() here because we want
- * the order to be:
- * 1) flush, 2) echo, 3) signal
- */
if (!L_NOFLSH(tty)) {
n_tty_flush_buffer(tty);
tty_driver_flush_buffer(tty);
@@ -1257,8 +1252,7 @@ send_signal:
echo_char(c, tty);
process_echoes(tty);
}
- if (tty->pgrp)
- kill_pgrp(tty->pgrp, signal, 1);
+ isig(signal, tty);
return;
}
}
--
1.8.1.2