Re: [PATCH v8 1/2] seccomp: add a return code to trap to userspace

Oleg Nesterov
2018-11-01T13:56:41Z

On 10/29, Tycho Andersen wrote:
>
> +static int seccomp_notify_release(struct inode *inode, struct file *file)
> +{
> + struct seccomp_filter *filter = file->private_data;
> + struct seccomp_knotif *knotif;
> +
> + mutex_lock(&filter->notify_lock);
> +
> + /*
> + * If this file is being closed because e.g. the task who owned it
> + * died, let's wake everyone up who was waiting on us.
> + */
> + list_for_each_entry(knotif, &filter->notif->notifications, list) {
> + if (knotif->state == SECCOMP_NOTIFY_REPLIED)
> + continue;
> +
> + knotif->state = SECCOMP_NOTIFY_REPLIED;
> + knotif->error = -ENOSYS;
> + knotif->val = 0;
> +
> + complete(&knotif->ready);
> + }
> +
> + wake_up_all(&filter->notif->wqh);

Why? __fput() is not possible if there is another user of this file sleeping
in seccomp_notify_poll().

> + kfree(filter->notif);

Hmm, this looks wrong... we can't kfree ->notif if its ->notifications list
is not empty, otherwise seccomp_do_user_notification()->list_del(&n.list)
can write to the freed memory.

I think _release() should do list_for_each_entry_safe() + list_del_init()
and seccomp_do_user_notification() should use list_del_init() too.

Or, simpler, seccomp_do_user_notification() should do

if (!match->notif)
goto out;

instead of "goto remove_list".

Oleg.