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n_tty: Access termios values safely
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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 <[email protected]>
Signed-off-by: Greg Kroah-Hartman <[email protected]>
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peterhurley authored and gregkh committed Jul 23, 2013
1 parent 6a1c068 commit 9356b53
Showing 1 changed file with 39 additions and 5 deletions.
44 changes: 39 additions & 5 deletions drivers/tty/n_tty.c
Original file line number Diff line number Diff line change
Expand Up @@ -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);
Expand All @@ -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,
Expand All @@ -1512,13 +1518,17 @@ 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;
count = min(count, room);
if (count)
__receive_buf(tty, cp, fp, count);

up_read(&tty->termios_rwsem);

return count;
}

Expand Down Expand Up @@ -1934,6 +1944,8 @@ static ssize_t n_tty_read(struct tty_struct *tty, struct file *file,
if (c < 0)
return c;

down_read(&tty->termios_rwsem);

minimum = time = 0;
timeout = MAX_SCHEDULE_TIMEOUT;
if (!ldata->icanon) {
Expand All @@ -1955,11 +1967,15 @@ static ssize_t n_tty_read(struct tty_struct *tty, struct file *file,
* 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;

Expand Down Expand Up @@ -2009,7 +2025,11 @@ static ssize_t n_tty_read(struct tty_struct *tty, struct file *file,
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);
Expand Down Expand Up @@ -2048,13 +2068,17 @@ static ssize_t n_tty_read(struct tty_struct *tty, struct file *file,
* 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);
Expand All @@ -2076,10 +2100,13 @@ static ssize_t n_tty_read(struct tty_struct *tty, struct file *file,
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;
}

Expand Down Expand Up @@ -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);

Expand Down Expand Up @@ -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;
}

Expand Down

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