linux-kernel - Re: [PATCH 1/3] seccomp: interrupt SECCOMP_IOCTL_NOTIF

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Message-ID: <CAEWA0a43nYT+YVXWLhv8THL+gu3QLVKznPppjQ_mWina2c-HJw@mail.gmail.com>
Date: Fri, 24 May 2024 10:47:47 -0700
From: Andrei Vagin <avagin@...gle.com>
To: Oleg Nesterov <oleg@...hat.com>
Cc: Kees Cook <keescook@...omium.org>, Andy Lutomirski <luto@...capital.net>, 
	Will Drewry <wad@...omium.org>, Christian Brauner <brauner@...nel.org>, linux-kernel@...r.kernel.org, 
	Tycho Andersen <tandersen@...flix.com>, Jens Axboe <axboe@...nel.dk>
Subject: Re: [PATCH 1/3] seccomp: interrupt SECCOMP_IOCTL_NOTIF_RECV when all
 users have exited

On Thu, May 23, 2024 at 2:00 AM Oleg Nesterov <oleg@...hat.com> wrote:
>
> Hi Andrei,
>
> the patch looks good to me even if I don't really understand what
> SECCOMP_IOCTL_NOTIF_RECV does. But let me ask a stupid question,
>
> On 05/23, Andrei Vagin wrote:
> >
> > The change is based on the 'commit 99cdb8b9a573 ("seccomp: notify about
> > unused filter")' which implemented (E)POLLHUP notifications.
>
> To me this patch fixes the commit above, because without this change

It depends on how we look at it. I think the intention was to address
the epoll/poll/select syscalls to return (E)POLLHUP notifications when
filters have been orphaned. Plus, this code looked a bit different that
time and recv_wake_function used another notification mechanism.

>
> > @@ -1466,7 +1466,7 @@ static int recv_wake_function(wait_queue_entry_t *wait, unsigned int mode, int s
> >                                 void *key)
> >  {
> >       /* Avoid a wakeup if event not interesting for us. */
> > -     if (key && !(key_to_poll(key) & (EPOLLIN | EPOLLERR)))
> > +     if (key && !(key_to_poll(key) & (EPOLLIN | EPOLLERR | EPOLLHUP)))
>
> __seccomp_filter_orphan() -> wake_up_poll(&orig->wqh, EPOLLHUP) won't
> wakeup the task sleeping in recv_wait_event(), right ?
>
> In any case, FWIW
>
> Reviewed-by: Oleg Nesterov <oleg@...hat.com>

Thanks,
Andrei