From: "Michael Kerrisk (man-pages)" <mtk.manpages@gmail.com>
To: Tycho Andersen <tycho@tycho.ws>
Cc: mtk.manpages@gmail.com, "Serge E. Hallyn" <serge@hallyn.com>,
linux-man@vger.kernel.org, Kees Cook <keescook@chromium.org>,
Linux API <linux-api@vger.kernel.org>,
lkml <linux-kernel@vger.kernel.org>,
Andy Lutomirski <luto@amacapital.net>, Jann Horn <jann@thejh.net>,
Oleg Nesterov <oleg@redhat.com>,
Christian Brauner <christian@brauner.io>,
"Eric W. Biederman" <ebiederm@xmission.com>,
Containers <containers@lists.linux-foundation.org>,
Aleksa Sarai <asarai@suse.de>,
Tyler Hicks <tyhicks@canonical.com>,
Akihiro Suda <suda.akihiro@lab.ntt.co.jp>
Subject: Re: [PATCH 2/2] seccomp.2: document userspace notification
Date: Fri, 1 Mar 2019 16:13:46 +0100 [thread overview]
Message-ID: <7a101bfc-b045-35f8-aa3f-a18ecc896fc8@gmail.com> (raw)
In-Reply-To: <20190301145341.GD7413@cisco>
On 3/1/19 3:53 PM, Tycho Andersen wrote:
> On Thu, Feb 28, 2019 at 02:25:55PM +0100, Michael Kerrisk (man-pages) wrote:
>>> 7. The monitoring process can use the information in the
>>> 'struct seccomp_notif' to make a determination about the
>>> system call being made by the target process. This
>>> structure includes a 'data' field that is the same
>>> 'struct seccomp_data' that is passed to a BPF filter.
>>>
>>> In addition, the monitoring process may make use of other
>>> information that is available from user space. For example,
>>> it may inspect the memory of the target process (whose PID
>>> is provided in the 'struct seccomp_notif') using
>>> /proc/PID/mem, which includes inspecting the values
>>> pointed to by system call arguments (whose location is
>>> available 'seccomp_notif.data.args). However, when using
>>> the target process PID in this way, one must guard against
>>> PID re-use race conditions using the seccomp()
>>> SECCOMP_IOCTL_NOTIF_ID_VALID operation.
>>>
>>> 8. Having arrived at a decision about the target process's
>>> system call, the monitoring process can inform the kernel
>>> of its decision using the operation
>>>
>>> ioctl(listenfd, SECCOMP_IOCTL_NOTIF_SEND, respptr)
>>>
>>> where the third argument is a pointer to a
>>> 'struct seccomp_notif_resp'. [Some more details
>>> needed here, but I still don't yet understand fully
>>> the semantics of the 'error' and 'val' fields.]
>>
>> So clearly, I misunderstood these last two steps.
>>
>> (7) is something like: discover information in userspace
>> as required; perform userspace actions if appropriate
>> (perhaps doing the system call operation "on behalf of" the
>> target process).
>>
>>
>> (8) is something like:
>> set 'error' and 'val' to return info to the target process:
>> * error != 0 ==> make it look like the syscall failed,
>> with 'errno' set to that value
That piece should be amended:
error < 0 ==> make it look like syscall failed.
error > 0 ==> make it look like the syscall succeeded
and returned 'error'
Is that really supposed to happen?
>> * error == 0 ==> make it look like the syscall succeeded
>> and returned 'val'
Thanks,
Michael
--
Michael Kerrisk
Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/
Linux/UNIX System Programming Training: http://man7.org/training/
next prev parent reply other threads:[~2019-03-01 15:13 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <20181213001106.15268-1-tycho@tycho.ws>
[not found] ` <20181213001106.15268-3-tycho@tycho.ws>
2019-02-28 12:52 ` [PATCH 2/2] seccomp.2: document userspace notification Michael Kerrisk (man-pages)
2019-02-28 13:25 ` Michael Kerrisk (man-pages)
2019-03-01 14:53 ` Tycho Andersen
2019-03-01 15:13 ` Michael Kerrisk (man-pages) [this message]
2019-03-01 14:53 ` Tycho Andersen
2019-03-01 15:16 ` Michael Kerrisk (man-pages)
2019-03-01 15:19 ` Tycho Andersen
2019-03-01 16:02 ` Michael Kerrisk (man-pages)
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=7a101bfc-b045-35f8-aa3f-a18ecc896fc8@gmail.com \
--to=mtk.manpages@gmail.com \
--cc=asarai@suse.de \
--cc=christian@brauner.io \
--cc=containers@lists.linux-foundation.org \
--cc=ebiederm@xmission.com \
--cc=jann@thejh.net \
--cc=keescook@chromium.org \
--cc=linux-api@vger.kernel.org \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-man@vger.kernel.org \
--cc=luto@amacapital.net \
--cc=oleg@redhat.com \
--cc=serge@hallyn.com \
--cc=suda.akihiro@lab.ntt.co.jp \
--cc=tycho@tycho.ws \
--cc=tyhicks@canonical.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).