Claim a read lock on the tasklist_lock while setting the controlling terminal for the session leader. This fixes multiple races: 1. task_pgrp() and task_session() cannot be safely dereferenced, such as passing to get_pid(), without holding either rcu_read_lock() or tasklist_lock 2. setsid() unwisely allows any thread in the thread group to make the thread group leader the session leader; this makes the unlocked reads of ->signal->leader and signal->tty potentially unordered, stale or even have spurious values.
Signed-off-by: Peter Hurley <[email protected]> --- drivers/tty/tty_io.c | 23 +++++++++++++++++------ 1 file changed, 17 insertions(+), 6 deletions(-) diff --git a/drivers/tty/tty_io.c b/drivers/tty/tty_io.c index e33edfa..4226ae7 100644 --- a/drivers/tty/tty_io.c +++ b/drivers/tty/tty_io.c @@ -502,8 +502,15 @@ void proc_clear_tty(struct task_struct *p) tty_kref_put(tty); } -/* Called under the sighand lock */ - +/** + * proc_set_tty - set the controlling terminal + * + * Only callable by the session leader and only if it does not already have + * a controlling terminal. + * + * Caller must hold: a readlock on tasklist_lock + * sighand lock + */ static void __proc_set_tty(struct tty_struct *tty) { unsigned long flags; @@ -2158,6 +2165,7 @@ retry_open: mutex_lock(&tty_mutex); tty_lock(tty); + read_lock(&tasklist_lock); spin_lock_irq(¤t->sighand->siglock); if (!noctty && current->signal->leader && @@ -2165,6 +2173,7 @@ retry_open: tty->session == NULL) __proc_set_tty(tty); spin_unlock_irq(¤t->sighand->siglock); + read_unlock(&tasklist_lock); tty_unlock(tty); mutex_unlock(&tty_mutex); return 0; @@ -2454,10 +2463,13 @@ static int fionbio(struct file *file, int __user *p) static int tiocsctty(struct tty_struct *tty, int arg) { int ret = 0; - if (current->signal->leader && (task_session(current) == tty->session)) - return ret; mutex_lock(&tty_mutex); + read_lock(&tasklist_lock); + + if (current->signal->leader && (task_session(current) == tty->session)) + goto unlock; + /* * The process must be a session leader and * not have a controlling tty already. @@ -2476,9 +2488,7 @@ static int tiocsctty(struct tty_struct *tty, int arg) /* * Steal it away */ - read_lock(&tasklist_lock); session_clear_tty(tty->session); - read_unlock(&tasklist_lock); } else { ret = -EPERM; goto unlock; @@ -2486,6 +2496,7 @@ static int tiocsctty(struct tty_struct *tty, int arg) } proc_set_tty(tty); unlock: + read_unlock(&tasklist_lock); mutex_unlock(&tty_mutex); return ret; } -- 2.1.1 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
