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From: Christian Brauner <christian.brauner@ubuntu.com>
To: Jann Horn <jannh@google.com>
Cc: Kees Cook <keescook@chromium.org>,
	Sargun Dhillon <sargun@sargun.me>,
	Linux Containers <containers@lists.linux-foundation.org>,
	Aleksa Sarai <cyphar@cyphar.com>,
	Jeffrey Vander Stoep <jeffv@google.com>,
	Linux API <linux-api@vger.kernel.org>,
	kernel list <linux-kernel@vger.kernel.org>,
	Chris Palmer <palmer@google.com>,
	Robert Sesek <rsesek@google.com>, Tycho Andersen <tycho@tycho.ws>,
	Matt Denton <mpdenton@google.com>,
	Al Viro <viro@zeniv.linux.org.uk>
Subject: Re: [PATCH v2 2/3] seccomp: Introduce addfd ioctl to seccomp user notifier
Date: Sat, 30 May 2020 15:58:27 +0200	[thread overview]
Message-ID: <20200530135827.cxltfmiqara4yaki@wittgenstein> (raw)
In-Reply-To: <CAG48ez0+BvbLoSc+zcZwnwfOSCFt2LHnUkzzt-d4LQFJYXZC9w@mail.gmail.com>

On Sat, May 30, 2020 at 05:17:24AM +0200, Jann Horn wrote:
> On Sat, May 30, 2020 at 4:43 AM Kees Cook <keescook@chromium.org> wrote:
> > I mean, yes, that's certainly better, but it just seems a shame that
> > everyone has to do the get_unused/put_unused dance just because of how
> > SCM_RIGHTS does this weird put_user() in the middle.
> >
> > Can anyone clarify the expected failure mode from SCM_RIGHTS? Can we
> > move the put_user() after instead?
> 
> Honestly, I think trying to remove file descriptors and such after
> -EFAULT is a waste of time. If userspace runs into -EFAULT, userspace

Agreed, we've never bothered with trying to recover from EFAULT. Just
look at kernel/fork.c:_do_fork():
	if (clone_flags & CLONE_PARENT_SETTID)
		put_user(nr, args->parent_tid);

we don't even bother even though we technically could.

> is beyond saving and can't really do much other than exit immediately.
> There are a bunch of places that will change state and then throw
> -EFAULT at the end if userspace supplied an invalid address, because
> trying to hold locks across userspace accesses just in case userspace
> supplied a bogus address is kinda silly (and often borderline
> impossible).
> 
> You can actually see that even scm_detach_fds() currently just
> silently swallows errors if writing some header fields fails at the
> end.

There's really no point in trying to save a broken scm message imho.

  parent reply	other threads:[~2020-05-30 13:58 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 [this message]
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
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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