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

On Thu, Sep 27, 2018 at 5:11 PM Tycho Andersen [off-list ref] 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);