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n_tty: Lock access to tty->pgrp for POSIX job control 

Concurrent access to tty->pgrp must be protected with tty->ctrl_lock.
Also, as noted in the comments, reading current->signal->tty is
safe because either,
  1) current->signal->tty is assigned by current, or
  2) current->signal->tty is set to NULL.

NB: for reference, tty_check_change() implements a similar POSIX
check for the ioctls corresponding to tcflush(), tcdrain(),
tcsetattr(), tcsetpgrp(), tcflow() and tcsendbreak().

Signed-off-by: Peter Hurley <peter@hurleysoftware.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Peter Hurley 2013-03-06 08:38:20 -05:00 committed by Greg Kroah-Hartman
parent 8c985d18b1
commit 01a5e440c9
1 changed files with 18 additions and 16 deletions
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34
drivers/tty/n_tty.c
View File

@ -1719,10 +1719,9 @@ extern ssize_t redirected_tty_write(struct file *, const char __user *,
* and if appropriate send any needed signals and return a negative
* error code if action should be taken.
*
* FIXME:
* Locking: None - redirected write test is safe, testing
* current->signal should possibly lock current->sighand
* pgrp locking ?
* Locking: redirected write test is safe
* current->signal->tty check is safe
* ctrl_lock to safely reference tty->pgrp
*/
static int job_control(struct tty_struct *tty, struct file *file)
@ -1732,19 +1731,22 @@ static int job_control(struct tty_struct *tty, struct file *file)
/* NOTE: not yet done after every sleep pending a thorough
check of the logic of this change. -- jlc */
/* don't stop on /dev/console */
if (file->f_op->write != redirected_tty_write &&
current->signal->tty == tty) {
if (!tty->pgrp)
printk(KERN_ERR "n_tty_read: no tty->pgrp!\n");
else if (task_pgrp(current) != tty->pgrp) {
if (is_ignored(SIGTTIN) ||
is_current_pgrp_orphaned())
return -EIO;
kill_pgrp(task_pgrp(current), SIGTTIN, 1);
set_thread_flag(TIF_SIGPENDING);
return -ERESTARTSYS;
}
if (file->f_op->write == redirected_tty_write ||
current->signal->tty != tty)
return 0;
spin_lock_irq(&tty->ctrl_lock);
if (!tty->pgrp)
printk(KERN_ERR "n_tty_read: no tty->pgrp!\n");
else if (task_pgrp(current) != tty->pgrp) {
spin_unlock_irq(&tty->ctrl_lock);
if (is_ignored(SIGTTIN) || is_current_pgrp_orphaned())
return -EIO;
kill_pgrp(task_pgrp(current), SIGTTIN, 1);
set_thread_flag(TIF_SIGPENDING);
return -ERESTARTSYS;
}
spin_unlock_irq(&tty->ctrl_lock);
return 0;
}