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Date: Sat, 15 Jun 2013 09:14:24 -0400
From: Peter Hurley <peter@...leysoftware.com>
To: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc: linux-kernel@...r.kernel.org, linux-serial@...r.kernel.org,
Jiri Slaby <jslaby@...e.cz>,
Peter Hurley <peter@...leysoftware.com>
Subject: [PATCH v4 12/24] n_tty: Access termios values safely
Use termios_rwsem to guarantee safe access to the termios values.
This is particularly important for N_TTY as changing certain termios
settings alters the mode of operation.
termios_rwsem must be dropped across throttle/unthrottle since
those functions claim the termios_rwsem exclusively (to guarantee
safe access to the termios and for mutual exclusion).
Signed-off-by: Peter Hurley <peter@...leysoftware.com>
---
drivers/tty/n_tty.c | 44 +++++++++++++++++++++++++++++++++++++++-----
1 file changed, 39 insertions(+), 5 deletions(-)
diff --git a/drivers/tty/n_tty.c b/drivers/tty/n_tty.c
index ab923bb..0599b58 100644
--- a/drivers/tty/n_tty.c
+++ b/drivers/tty/n_tty.c
@@ -1491,10 +1491,14 @@ static void __receive_buf(struct tty_struct *tty, const unsigned char *cp,
* canonical mode and don't have a newline yet!
*/
while (1) {
+ int throttled;
tty_set_flow_change(tty, TTY_THROTTLE_SAFE);
if (receive_room(tty) >= TTY_THRESHOLD_THROTTLE)
break;
- if (!tty_throttle_safe(tty))
+ up_read(&tty->termios_rwsem);
+ throttled = tty_throttle_safe(tty);
+ down_read(&tty->termios_rwsem);
+ if (!throttled)
break;
}
__tty_set_flow_change(tty, 0);
@@ -1503,7 +1507,9 @@ static void __receive_buf(struct tty_struct *tty, const unsigned char *cp,
static void n_tty_receive_buf(struct tty_struct *tty, const unsigned char *cp,
char *fp, int count)
{
+ down_read(&tty->termios_rwsem);
__receive_buf(tty, cp, fp, count);
+ up_read(&tty->termios_rwsem);
}
static int n_tty_receive_buf2(struct tty_struct *tty, const unsigned char *cp,
@@ -1512,6 +1518,8 @@ static int n_tty_receive_buf2(struct tty_struct *tty, const unsigned char *cp,
struct n_tty_data *ldata = tty->disc_data;
int room;
+ down_read(&tty->termios_rwsem);
+
tty->receive_room = room = receive_room(tty);
if (!room)
ldata->no_room = 1;
@@ -1519,6 +1527,8 @@ static int n_tty_receive_buf2(struct tty_struct *tty, const unsigned char *cp,
if (count)
__receive_buf(tty, cp, fp, count);
+ up_read(&tty->termios_rwsem);
+
return count;
}
@@ -1934,6 +1944,8 @@ do_it_again:
if (c < 0)
return c;
+ down_read(&tty->termios_rwsem);
+
minimum = time = 0;
timeout = MAX_SCHEDULE_TIMEOUT;
if (!ldata->icanon) {
@@ -1955,11 +1967,15 @@ do_it_again:
* Internal serialization of reads.
*/
if (file->f_flags & O_NONBLOCK) {
- if (!mutex_trylock(&ldata->atomic_read_lock))
+ if (!mutex_trylock(&ldata->atomic_read_lock)) {
+ up_read(&tty->termios_rwsem);
return -EAGAIN;
+ }
} else {
- if (mutex_lock_interruptible(&ldata->atomic_read_lock))
+ if (mutex_lock_interruptible(&ldata->atomic_read_lock)) {
+ up_read(&tty->termios_rwsem);
return -ERESTARTSYS;
+ }
}
packet = tty->packet;
@@ -2009,7 +2025,11 @@ do_it_again:
break;
}
n_tty_set_room(tty);
+ up_read(&tty->termios_rwsem);
+
timeout = schedule_timeout(timeout);
+
+ down_read(&tty->termios_rwsem);
continue;
}
__set_current_state(TASK_RUNNING);
@@ -2048,13 +2068,17 @@ do_it_again:
* we won't get any more characters.
*/
while (1) {
+ int unthrottled;
tty_set_flow_change(tty, TTY_UNTHROTTLE_SAFE);
if (chars_in_buffer(tty) > TTY_THRESHOLD_UNTHROTTLE)
break;
if (!tty->count)
break;
n_tty_set_room(tty);
- if (!tty_unthrottle_safe(tty))
+ up_read(&tty->termios_rwsem);
+ unthrottled = tty_unthrottle_safe(tty);
+ down_read(&tty->termios_rwsem);
+ if (!unthrottled)
break;
}
__tty_set_flow_change(tty, 0);
@@ -2076,10 +2100,13 @@ do_it_again:
retval = size;
if (nr)
clear_bit(TTY_PUSH, &tty->flags);
- } else if (test_and_clear_bit(TTY_PUSH, &tty->flags))
+ } else if (test_and_clear_bit(TTY_PUSH, &tty->flags)) {
+ up_read(&tty->termios_rwsem);
goto do_it_again;
+ }
n_tty_set_room(tty);
+ up_read(&tty->termios_rwsem);
return retval;
}
@@ -2120,6 +2147,8 @@ static ssize_t n_tty_write(struct tty_struct *tty, struct file *file,
return retval;
}
+ down_read(&tty->termios_rwsem);
+
/* Write out any echoed characters that are still pending */
process_echoes(tty);
@@ -2173,13 +2202,18 @@ static ssize_t n_tty_write(struct tty_struct *tty, struct file *file,
retval = -EAGAIN;
break;
}
+ up_read(&tty->termios_rwsem);
+
schedule();
+
+ down_read(&tty->termios_rwsem);
}
break_out:
__set_current_state(TASK_RUNNING);
remove_wait_queue(&tty->write_wait, &wait);
if (b - buf != nr && tty->fasync)
set_bit(TTY_DO_WRITE_WAKEUP, &tty->flags);
+ up_read(&tty->termios_rwsem);
return (b - buf) ? b - buf : retval;
}
--
1.8.1.2
--
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