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From: Kees Cook <keescook@chromium.org>
To: Al Viro <viro@zeniv.linux.org.uk>
Cc: Sargun Dhillon <sargun@sargun.me>,
	christian.brauner@ubuntu.com,
	containers@lists.linux-foundation.org, cyphar@cyphar.com,
	jannh@google.com, jeffv@google.com, linux-api@vger.kernel.org,
	linux-kernel@vger.kernel.org, palmer@google.com,
	rsesek@google.com, tycho@tycho.ws,
	Matt Denton <mpdenton@google.com>
Subject: Re: [PATCH v2 2/3] seccomp: Introduce addfd ioctl to seccomp user notifier
Date: Sat, 30 May 2020 09:07:16 -0700	[thread overview]
Message-ID: <202005300834.6419E818A7@keescook> (raw)
In-Reply-To: <20200530140837.GM23230@ZenIV.linux.org.uk>

On Sat, May 30, 2020 at 03:08:37PM +0100, Al Viro wrote:
> On Fri, May 29, 2020 at 07:43:10PM -0700, Kees Cook wrote:
> 
> > Can anyone clarify the expected failure mode from SCM_RIGHTS? Can we
> > move the put_user() after instead? I think cleanup would just be:
> > replace_fd(fd, NULL, 0)
> 
> Bollocks.
> 
> Repeat after me: descriptor tables can be shared.  There is no
> "cleanup" after you've put something there.

Right -- this is what I was trying to ask about, and why I didn't like
the idea of just leaving the fd in the table on failure. But yeah, there
is a race if the process is about to fork or something.

So the choice here is how to handle the put_user() failure:

- add the put_user() address to the new helper, as I suggest in [1].
  (exactly duplicates current behavior)
- just leave the fd in place (not current behavior: dumps a fd into
  the process without "agreed" notification).
- do a double put_user (once before and once after), also in [1].
  (sort of a best-effort combo of the above two. and SCM_RIGHTS is
  hardly fast-pth).

-Kees

[1] https://lore.kernel.org/linux-api/202005282345.573B917@keescook/

-- 
Kees Cook

  reply	other threads:[~2020-05-30 16:07 UTC|newest]

Thread overview: 36+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-05-28 11:08 [PATCH v2 0/3] Add seccomp notifier ioctl that enables adding fds Sargun Dhillon
2020-05-28 11:08 ` [PATCH v2 1/3] seccomp: Add find_notification helper Sargun Dhillon
2020-05-29  6:23   ` Kees Cook
2020-05-29 17:40     ` Sargun Dhillon
2020-05-29 20:14       ` Kees Cook
2020-05-29  9:57   ` Christian Brauner
2020-05-28 11:08 ` [PATCH v2 2/3] seccomp: Introduce addfd ioctl to seccomp user notifier Sargun Dhillon
2020-05-29  7:31   ` Kees Cook
2020-05-29  7:38     ` Christian Brauner
2020-05-29  7:45       ` Kees Cook
2020-05-30  1:10     ` Sargun Dhillon
2020-05-30  2:43       ` Kees Cook
2020-05-30  3:17         ` Jann Horn
2020-05-30  5:22           ` Kees Cook
2020-05-30 13:58           ` Christian Brauner
2020-05-30 16:09             ` Kees Cook
2020-05-30  3:58         ` Sargun Dhillon
2020-05-30  5:47           ` Kees Cook
2020-05-30 14:13             ` Christian Brauner
2020-05-30 16:14               ` Kees Cook
2020-05-30 16:21                 ` Christian Brauner
2020-05-30 14:08         ` Al Viro
2020-05-30 16:07           ` Kees Cook [this message]
2020-06-01 19:02             ` Sargun Dhillon
2020-06-01 19:59               ` Kees Cook
2020-05-29  9:24   ` Giuseppe Scrivano
2020-05-29 10:32   ` Christian Brauner
2020-05-29 13:31     ` Christian Brauner
2020-05-29 22:35       ` Sargun Dhillon
2020-05-28 11:08 ` [PATCH v2 3/3] selftests/seccomp: Test SECCOMP_IOCTL_NOTIF_ADDFD Sargun Dhillon
2020-05-29  7:41   ` Kees Cook
2020-05-29 13:29     ` Tycho Andersen
2020-05-29 18:46     ` Sargun Dhillon
2020-05-29 19:12       ` Tycho Andersen
2020-05-29 20:09       ` Kees Cook
2020-05-29 13:30 ` [PATCH v2 0/3] Add seccomp notifier ioctl that enables adding fds Tycho Andersen

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