linux-kernel - Re: [PATCH v2 3/3] selftests/seccomp: Test SECCOMP_IOCTL_NOTIF

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Message-ID: <20200529191207.GH429721@cisco>
Date:   Fri, 29 May 2020 13:12:07 -0600
From:   Tycho Andersen <tycho@...ho.ws>
To:     Sargun Dhillon <sargun@...gun.me>
Cc:     Kees Cook <keescook@...omium.org>, christian.brauner@...ntu.com,
        containers@...ts.linux-foundation.org, cyphar@...har.com,
        jannh@...gle.com, jeffv@...gle.com, linux-api@...r.kernel.org,
        linux-kernel@...r.kernel.org, palmer@...gle.com, rsesek@...gle.com,
        Matt Denton <mpdenton@...gle.com>
Subject: Re: [PATCH v2 3/3] selftests/seccomp: Test SECCOMP_IOCTL_NOTIF_ADDFD

On Fri, May 29, 2020 at 06:46:07PM +0000, Sargun Dhillon wrote:
> On Fri, May 29, 2020 at 12:41:51AM -0700, Kees Cook wrote:
> > On Thu, May 28, 2020 at 04:08:58AM -0700, Sargun Dhillon wrote:
> > > +	EXPECT_EQ(ioctl(listener, SECCOMP_IOCTL_NOTIF_SEND, &resp), 0);
> > > +
> > > +	nextid = req.id + 1;
> > > +
> > > +	/* Wait for getppid to be called for the second time */
> > > +	sleep(1);
> > 
> > I always rebel at finding "sleep" in tests. ;) Is this needed? IIUC,
> > userspace will immediately see EINPROGRESS after the NOTIF_SEND
> > finishes, yes?
> > 
> > Otherwise, yes, this looks good.
> > 
> > -- 
> > Kees Cook
> I'm open to better suggestions, but there's a race where if getppid
> is not called before the second SECCOMP_IOCTL_NOTIF_ADDFD is called,
> you will just get an ENOENT, since the notification ID is not found.

Ah, I see. The goal is to test the -EINPROGRESS here.

If you use write() instead of getppid(), and write to a socket, will
that work? The parent can block for the read, and once some thing has
been read it can test for -EINPROGRESS.

The user_notification_signal test does something similar.

Tycho