linux-kernel - Re: [PATCH 2/2] seccomp.2: document userspace notification

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Message-ID: <20190301151937.GE7413@cisco>
Date:   Fri, 1 Mar 2019 08:19:37 -0700
From:   Tycho Andersen <tycho@...ho.ws>
To:     "Michael Kerrisk (man-pages)" <mtk.manpages@...il.com>
Cc:     "Serge E. Hallyn" <serge@...lyn.com>, linux-man@...r.kernel.org,
        Kees Cook <keescook@...omium.org>,
        Linux API <linux-api@...r.kernel.org>,
        lkml <linux-kernel@...r.kernel.org>,
        Andy Lutomirski <luto@...capital.net>,
        Jann Horn <jann@...jh.net>, Oleg Nesterov <oleg@...hat.com>,
        Christian Brauner <christian@...uner.io>,
        "Eric W. Biederman" <ebiederm@...ssion.com>,
        Containers <containers@...ts.linux-foundation.org>,
        Aleksa Sarai <asarai@...e.de>,
        Tyler Hicks <tyhicks@...onical.com>,
        Akihiro Suda <suda.akihiro@....ntt.co.jp>
Subject: Re: [PATCH 2/2] seccomp.2: document userspace notification

On Fri, Mar 01, 2019 at 04:16:27PM +0100, Michael Kerrisk (man-pages) wrote:
> Hello Tycho,
> 
> On 3/1/19 3:53 PM, Tycho Andersen wrote:
> > On Thu, Feb 28, 2019 at 01:52:19PM +0100, Michael Kerrisk (man-pages) wrote:
> >>> +a notification will be sent to this fd. See "Userspace Notification" below for
> >>
> >> s/fd/file descriptor/ throughout please.
> > 
> > Will do.
> > 
> >>> +more details.
> >>
> >> I think the description here could be better worded as something like:
> >>
> >>     SECCOMP_FILTER_FLAG_NEW_LISTENER
> >>         Register a new filter, as usual, but on success return a
> >>         new file descriptor that provides user-space notifications.
> >>         When the filter returns SECCOMP_RET_USER_NOTIF, a notification
> >>         will be provided via this file descriptor. The close-on-exec
> >>         flag is automatically set on the new file descriptor. ...
> >>
> >>>  .RE
> >>>  .TP
> >>>  .BR SECCOMP_GET_ACTION_AVAIL " (since Linux 4.14)"
> >>> @@ -606,6 +613,17 @@ file.
> >>>  .TP
> >>>  .BR SECCOMP_RET_ALLOW
> >>>  This value results in the system call being executed.
> >>> +.TP
> >>> +.BR SECCOMP_RET_USER_NOTIF " (since Linux 4.21)"
> >>
> >> Please see the start of this hanging list in the manual page.
> >> Can you confirm that SECCOMP_RET_USER_NOTIF really is the lowest
> >> in the precedence order of all of the filter return values?
> > 
> > Oh, no, I didn't realize it was in a particular order. I'll switch it.
> 
> Just for my immediate education (I'm experimenting right now),
> where/how does it fit in the precedence order?

In between RET_ERRNO and RET_TRACE; see include/uapi/linux/seccomp.h
for details.

Tycho