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    SubjectRe: [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.
    >
    > The other approach is to "poll" the child, and wait for it to enter
    > the second syscall. Calling receive beforehand doesn't work because
    > it moves the state of the notification in the kernel to received,
    > and then the kernel doesn't error with EINPROGRESS.

    For tests, I prefer polling. How about adding a busy-loop
    (with a iteration-bounded small usleep) that just calls
    SECCOMP_IOCTL_NOTIF_ID_VALID until it's valid?

    --
    Kees Cook

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