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

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Date:   Fri, 1 Mar 2019 17:02:05 +0100
From:   "Michael Kerrisk (man-pages)" <mtk.manpages@...il.com>
To:     Tycho Andersen <tycho@...ho.ws>
Cc:     mtk.manpages@...il.com, "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 3/1/19 4:19 PM, Tycho Andersen wrote:
> 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.

Confirmed by experiment :-).

Cheers,

Michael


-- 
Michael Kerrisk
Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/
Linux/UNIX System Programming Training: http://man7.org/training/