On Mon, Apr 26, 2021 at 11:06:07AM -0700, Sargun Dhillon wrote:
> @@ -1103,11 +1111,31 @@ static int seccomp_do_user_notification(int this_syscall,
> * This is where we wait for a reply from userspace.
> */
> do {
> + interruptible = notification_interruptible(&n);
> +
> mutex_unlock(&match->notify_lock);
> - err = wait_for_completion_interruptible(&n.ready);
> + if (interruptible)
> + err = wait_for_completion_interruptible(&n.ready);
> + else
> + err = wait_for_completion_killable(&n.ready);
> mutex_lock(&match->notify_lock);
> - if (err != 0)
> +
> + if (err != 0) {
> + /*
> + * There is a race condition here where if the
> + * notification was received with the
> + * SECCOMP_USER_NOTIF_FLAG_WAIT_KILLABLE flag, but a
> + * non-fatal signal was received before we could
> + * transition we could erroneously end our wait early.
> + *
> + * The next wait for completion will ensure the signal
> + * was not fatal.
> + */
> + if (interruptible && !notification_interruptible(&n))
> + continue;
I'm trying to understand how one would hit this race,
> @@ -1457,6 +1487,12 @@ static long seccomp_notify_recv(struct seccomp_filter *filter,
> unotif.pid = task_pid_vnr(knotif->task);
> unotif.data = *(knotif->data);
>
> + if (unotif.flags & SECCOMP_USER_NOTIF_FLAG_WAIT_KILLABLE) {
> + knotif->wait_killable = true;
> + complete(&knotif->ready);
> + }
> +
> +
> knotif->state = SECCOMP_NOTIFY_SENT;
> wake_up_poll(&filter->wqh, EPOLLOUT | EPOLLWRNORM);
> ret = 0;
Seems like the idea is that if someone does a ioctl(RECV, ...) twice
they'll hit it? But doesn't the test for NOTIFY_INIT and return
-ENOENT above this hunk prevent that?
Thanks,
Tycho
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