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

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Date:   Fri, 1 Mar 2019 16:16:27 +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

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?


Thanks,

Michael

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