Re: [PATCH v7 5/6] seccomp: add a way to pass FDs via a notification fd

Jann Horn
2018-09-27T19:28:38Z

On Thu, Sep 27, 2018 at 5:11 PM Tycho Andersen <tycho@tycho.ws> wrote:
> This patch adds a way to insert FDs into the tracee's process (also
> close/overwrite fds for the tracee). This functionality is necessary to
> mock things like socketpair() or dup2() or similar, but since it depends on
> external (vfs) patches, I've left it as a separate patch as before so the
> core functionality can still be merged while we argue about this. Except
> this time it doesn't add any ugliness to the API :)
[...]
> +static long seccomp_notify_put_fd(struct seccomp_filter *filter,
> + unsigned long arg)
> +{
> + struct seccomp_notif_put_fd req;
> + void __user *buf = (void __user *)arg;
> + struct seccomp_knotif *knotif = NULL;
> + long ret;
> +
> + if (copy_from_user(&req, buf, sizeof(req)))
> + return -EFAULT;
> +
> + if (req.fd < 0 && req.to_replace < 0)
> + return -EINVAL;
> +
> + ret = mutex_lock_interruptible(&filter->notify_lock);
> + if (ret < 0)
> + return ret;
> +
> + ret = -ENOENT;
> + list_for_each_entry(knotif, &filter->notif->notifications, list) {
> + struct file *file = NULL;
> +
> + if (knotif->id != req.id)
> + continue;

Are you intentionally permitting non-SENT states here? It shouldn't
make a big difference, but I think it'd be nice to at least block the
use of notifications in SECCOMP_NOTIFY_REPLIED state.

> + if (req.fd >= 0)
> + file = fget(req.fd);