From: Daniel Colascione <dancol@google.com>
To: Andy Lutomirski <luto@amacapital.net>
Cc: Jann Horn <jannh@google.com>,
Joel Fernandes <joel@joelfernandes.org>,
kernel list <linux-kernel@vger.kernel.org>,
John Reck <jreck@google.com>,
John Stultz <john.stultz@linaro.org>,
Todd Kjos <tkjos@google.com>,
Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
Christoph Hellwig <hch@infradead.org>,
Al Viro <viro@zeniv.linux.org.uk>,
Andrew Morton <akpm@linux-foundation.org>,
Bruce Fields <bfields@fieldses.org>,
Jeff Layton <jlayton@kernel.org>,
Khalid Aziz <khalid.aziz@oracle.com>,
Lei.Yang@windriver.com, linux-fsdevel@vger.kernel.org,
linux-kselftest@vger.kernel.org, Linux-MM <linux-mm@kvack.org>,
marcandre.lureau@redhat.com,
Mike Kravetz <mike.kravetz@oracle.com>,
Minchan Kim <minchan@kernel.org>, Shuah Khan <shuah@kernel.org>,
valdis.kletnieks@vt.edu, Hugh Dickins <hughd@google.com>,
Linux API <linux-api@vger.kernel.org>
Subject: Re: [PATCH v3 resend 1/2] mm: Add an F_SEAL_FUTURE_WRITE seal to memfd
Date: Fri, 9 Nov 2018 14:42:18 -0800 [thread overview]
Message-ID: <CAKOZuetZrL10zWwn4Jzzg0QL2nd3Fm0JxGtzC79SZAfOK525Ag@mail.gmail.com> (raw)
In-Reply-To: <BB64C995-F374-49EB-8469-4820231D8152@amacapital.net>
On Fri, Nov 9, 2018 at 2:37 PM, Andy Lutomirski <luto@amacapital.net> wrote:
>> Another, more general fix might be to prevent /proc/pid/fd/N opens
>> from "upgrading" access modes. But that'd be a bigger ABI break.
>
> I think we should fix that, too. I consider it a bug fix, not an ABI break, personally.
Someone, somewhere is probably relying on it though, and that means
that we probably can't change it unless it's actually causing
problems.
<mumble>spacebar heating</mumble>
>>> That aside: I wonder whether a better API would be something that
>>> allows you to create a new readonly file descriptor, instead of
>>> fiddling with the writability of an existing fd.
>>
>> That doesn't work, unfortunately. The ashmem API we're replacing with
>> memfd requires file descriptor continuity. I also looked into opening
>> a new FD and dup2(2)ing atop the old one, but this approach doesn't
>> work in the case that the old FD has already leaked to some other
>> context (e.g., another dup, SCM_RIGHTS). See
>> https://developer.android.com/ndk/reference/group/memory. We can't
>> break ASharedMemory_setProt.
>
>
> Hmm. If we fix the general reopen bug, a way to drop write access from an existing struct file would do what Android needs, right? I don’t know if there are general VFS issues with that.
I also proposed that. :-) Maybe it'd work best as a special case of
the perennial revoke(2) that people keep proposing. You'd be able to
selectively revoke all access or just write access.
next prev parent reply other threads:[~2018-11-09 22:42 UTC|newest]
Thread overview: 32+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-11-08 4:15 [PATCH v3 resend 1/2] mm: Add an F_SEAL_FUTURE_WRITE seal to memfd Joel Fernandes (Google)
2018-11-08 4:15 ` [PATCH v3 resend 2/2] selftests/memfd: Add tests for F_SEAL_FUTURE_WRITE seal Joel Fernandes (Google)
2018-11-09 8:49 ` [PATCH v3 resend 1/2] mm: Add an F_SEAL_FUTURE_WRITE seal to memfd Joel Fernandes
2018-11-09 20:36 ` Andrew Morton
2018-11-10 3:54 ` Joel Fernandes
2018-11-09 21:06 ` Jann Horn
2018-11-09 21:19 ` Jann Horn
2018-11-10 3:20 ` Joel Fernandes
2018-11-10 6:05 ` Andy Lutomirski
2018-11-10 18:24 ` Joel Fernandes
2018-11-10 18:45 ` Daniel Colascione
2018-11-10 19:11 ` Daniel Colascione
2018-11-10 19:55 ` Andy Lutomirski
2018-11-10 22:09 ` Joel Fernandes
2018-11-10 22:18 ` Andy Lutomirski
2018-11-11 2:38 ` Joel Fernandes
2018-11-11 3:40 ` Andy Lutomirski
2018-11-11 4:01 ` Joel Fernandes
2018-11-11 8:09 ` Joel Fernandes
2018-11-11 8:30 ` Daniel Colascione
2018-11-11 15:14 ` Andy Lutomirski
2018-11-11 17:36 ` Joel Fernandes
[not found] ` <CAKOZuethC7+YrRyyGciUCfhSSa9cCcAFJ8g_qEw9uh3TBbyOcg@mail.gmail.com>
2018-11-10 17:10 ` Joel Fernandes
2018-11-09 21:40 ` Andy Lutomirski
2018-11-09 20:02 ` Michael Tirado
2018-11-10 1:49 ` Joel Fernandes
2018-11-09 22:20 ` Daniel Colascione
2018-11-09 22:37 ` Andy Lutomirski
2018-11-09 22:42 ` Daniel Colascione [this message]
2018-11-09 23:14 ` Andy Lutomirski
2018-11-10 1:36 ` Joel Fernandes
2018-11-09 23:46 ` Joel Fernandes
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