Commit 4943b66d authored by Andrei Vagin's avatar Andrei Vagin Committed by Kees Cook
Browse files

seccomp: don't use semaphore and wait_queue together 



The main reason is to use new wake_up helpers that will be added in the
following patches. But here are a few other reasons:

* if we use two different ways, we always need to call them both. This
  patch fixes seccomp_notify_recv where we forgot to call wake_up_poll
  in the error path.

* If we use one primitive, we can control how many waiters are woken up
  for each request. Our goal is to wake up just one that will handle a
  request. Right now, wake_up_poll can wake up one waiter and
  up(&match->notif->request) can wake up one more.

Signed-off-by: default avatarAndrei Vagin <avagin@google.com>
Acked-by: default avatar"Peter Zijlstra (Intel)" <peterz@infradead.org>
Link: https://lore.kernel.org/r/20230308073201.3102738-2-avagin@google.com


Signed-off-by: default avatarKees Cook <keescook@chromium.org>
parent fdf0eaf1

kernel/seccomp.c

+36 −5
Original line number Diff line number Diff line
@@ -145,7 +145,7 @@ struct seccomp_kaddfd { 
 * @notifications: A list of struct seccomp_knotif elements.

 */

struct notification {

	struct semaphore request;

	atomic_t requests;

	u64 next_id;

	struct list_head notifications;

};
@@ -1116,7 +1116,7 @@ static int seccomp_do_user_notification(int this_syscall, 
	list_add_tail(&n.list, &match->notif->notifications);

	INIT_LIST_HEAD(&n.addfd);



	up(&match->notif->request);

	atomic_inc(&match->notif->requests);

	wake_up_poll(&match->wqh, EPOLLIN | EPOLLRDNORM);



	/*
@@ -1450,6 +1450,37 @@ find_notification(struct seccomp_filter *filter, u64 id) 
	return NULL;

}



static int recv_wake_function(wait_queue_entry_t *wait, unsigned int mode, int sync,

				  void *key)

{

	/* Avoid a wakeup if event not interesting for us. */

	if (key && !(key_to_poll(key) & (EPOLLIN | EPOLLERR)))

		return 0;

	return autoremove_wake_function(wait, mode, sync, key);

}



static int recv_wait_event(struct seccomp_filter *filter)

{

	DEFINE_WAIT_FUNC(wait, recv_wake_function);

	int ret;



	if (atomic_dec_if_positive(&filter->notif->requests) >= 0)

		return 0;



	for (;;) {

		ret = prepare_to_wait_event(&filter->wqh, &wait, TASK_INTERRUPTIBLE);



		if (atomic_dec_if_positive(&filter->notif->requests) >= 0)

			break;



		if (ret)

			return ret;



		schedule();

	}

	finish_wait(&filter->wqh, &wait);

	return 0;

}



static long seccomp_notify_recv(struct seccomp_filter *filter,

				void __user *buf)
@@ -1467,7 +1498,7 @@ static long seccomp_notify_recv(struct seccomp_filter *filter, 


	memset(&unotif, 0, sizeof(unotif));



	ret = down_interruptible(&filter->notif->request);

	ret = recv_wait_event(filter);

	if (ret < 0)

		return ret;
@@ -1515,7 +1546,8 @@ static long seccomp_notify_recv(struct seccomp_filter *filter, 
			if (should_sleep_killable(filter, knotif))

				complete(&knotif->ready);

			knotif->state = SECCOMP_NOTIFY_INIT;

			up(&filter->notif->request);

			atomic_inc(&filter->notif->requests);

			wake_up_poll(&filter->wqh, EPOLLIN | EPOLLRDNORM);

		}

		mutex_unlock(&filter->notify_lock);

	}
@@ -1777,7 +1809,6 @@ static struct file *init_listener(struct seccomp_filter *filter) 
	if (!filter->notif)

		goto out;



	sema_init(&filter->notif->request, 0);

	filter->notif->next_id = get_random_u64();

	INIT_LIST_HEAD(&filter->notif->notifications);