From: Tycho Andersen <tycho@tycho.ws>
To: "Michael Kerrisk (man-pages)" <mtk.manpages@gmail.com>
Cc: "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 07:53:41 -0700 [thread overview]
Message-ID: <20190301145341.GD7413@cisco> (raw)
In-Reply-To: <e7a5abd9-f7b7-e077-221a-4c3ef7b818df@gmail.com>
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
> * error == 0 ==> make it look like the syscall succeeded
> and returned 'val'
>
> Right?
Yep, exactly.
Tycho
next prev parent reply other threads:[~2019-03-01 14:53 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 [this message]
2019-03-01 15:13 ` Michael Kerrisk (man-pages)
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)
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