Documentation: seccomp: Fix user notification documentation

The documentation had some previously incorrect information about how
userspace notifications (and responses) were handled due to a change
from a previously proposed patchset.

Signed-off-by: Sargun Dhillon <sargun@sargun.me>
Acked-by: Tycho Andersen <tycho@tycho.pizza>
Acked-by: Christian Brauner <christian.brauner@ubuntu.com>
Signed-off-by: Kees Cook <keescook@chromium.org>
Fixes: 6a21cc5 ("seccomp: add a return code to trap to userspace")
Cc: stable@vger.kernel.org
Link: https://lore.kernel.org/r/20210517193908.3113-2-sargun@sargun.me

Documentation/userspace-api/seccomp_filter.rst

@@ -250,14 +250,14 @@ Users can read via ``ioctl(SECCOMP_IOCTL_NOTIF_RECV)``  (or ``poll()``) on a
 seccomp notification fd to receive a ``struct seccomp_notif``, which contains
 five members: the input length of the structure, a unique-per-filter ``id``,
 the ``pid`` of the task which triggered this request (which may be 0 if the
-task is in a pid ns not visible from the listener's pid namespace), a ``flags``
-member which for now only has ``SECCOMP_NOTIF_FLAG_SIGNALED``, representing
-whether or not the notification is a result of a non-fatal signal, and the
-``data`` passed to seccomp. Userspace can then make a decision based on this
-information about what to do, and ``ioctl(SECCOMP_IOCTL_NOTIF_SEND)`` a
-response, indicating what should be returned to userspace. The ``id`` member of
-``struct seccomp_notif_resp`` should be the same ``id`` as in ``struct
-seccomp_notif``.
+task is in a pid ns not visible from the listener's pid namespace). The
+notification also contains the ``data`` passed to seccomp, and a filters flag.
+The structure should be zeroed out prior to calling the ioctl.
+
+Userspace can then make a decision based on this information about what to do,
+and ``ioctl(SECCOMP_IOCTL_NOTIF_SEND)`` a response, indicating what should be
+returned to userspace. The ``id`` member of ``struct seccomp_notif_resp`` should
+be the same ``id`` as in ``struct seccomp_notif``.
 
 It is worth noting that ``struct seccomp_data`` contains the values of register
 arguments to the syscall, but does not contain pointers to memory. The task's