From: Christian Brauner <christian.brauner@ubuntu.com>
To: Daniel Colascione <dancol@google.com>
Cc: Minchan Kim <minchan@kernel.org>,
Kirill Tkhai <ktkhai@virtuozzo.com>,
Michal Hocko <mhocko@suse.com>,
Andrew Morton <akpm@linux-foundation.org>,
LKML <linux-kernel@vger.kernel.org>,
linux-mm <linux-mm@kvack.org>,
Linux API <linux-api@vger.kernel.org>,
oleksandr@redhat.com, Suren Baghdasaryan <surenb@google.com>,
Tim Murray <timmurray@google.com>,
Sandeep Patil <sspatil@google.com>,
Sonny Rao <sonnyrao@google.com>,
Brian Geffon <bgeffon@google.com>,
Johannes Weiner <hannes@cmpxchg.org>,
Shakeel Butt <shakeelb@google.com>,
John Dias <joaodias@google.com>
Subject: Re: [PATCH 2/4] mm: introduce external memory hinting API
Date: Tue, 14 Jan 2020 20:20:57 +0100 [thread overview]
Message-ID: <20200114192056.b6wi4adsps6xi4t4@wittgenstein> (raw)
In-Reply-To: <CAKOZueu=U4c2URaq8Pz-B00XV+TxaKwHRNXv3BUiDbQrLQpJ3A@mail.gmail.com>
On Mon, Jan 13, 2020 at 01:04:44PM -0800, Daniel Colascione wrote:
> On Mon, Jan 13, 2020 at 12:42 PM Christian Brauner
> <christian.brauner@ubuntu.com> wrote:
> >
> > On Mon, Jan 13, 2020 at 11:27:03AM -0800, Daniel Colascione wrote:
> > > On Mon, Jan 13, 2020 at 11:10 AM Christian Brauner
> > > <christian.brauner@ubuntu.com> wrote:
> > > > This does not
> > > > affect the permission checking you're performing here.
> > >
> > > Pidfds-as-capabilities sounds like a good change. Can you clarify what
> > > you mean here though? Do you mean that in order to perform some
> > > process-directed operation X on process Y, the pidfd passed to X must
> > > have been opened with PIDFD_CAP_X *and* the process *using* the pidfds
> > > must be able to perform operation X on process Y? Or do pidfds in this
> > > model "carry" permissions in the same way that an ordinary file
> > > descriptor "carries" the ability to write to a file if it was opened
> > > with O_WRONLY even if the FD is passed to a process that couldn't
> > > otherwise write to that file? Right now, pidfds are identity-only and
> > > always rely on the caller's permissions. I like the capability bit
> > > model because it makes pidfds more consistent with other file
> > > descriptors and enabled delegation of capabilities across the system.
> >
> > I'm going back and forth on this. My initial implementation has it that
> > you'd need both, PIDFD_FLAG/CAP_X and the process using the pidfd must
> > be able to perform the operation X on process Y. The alternative becomes
> > tricky for e.g. anything that requires ptrace_may_access() permissions
> > such as getting an fd out from another task based on its pidfd and so
> > on.
>
> I think the alternative is necessary though. What's the point of the
> pidfd capability bits if they don't grant access? If I have a pidfd
> for Y that doesn't let me do operation X, but I have ambient authority
> to do Y anyway, then I can just make my own pidfd for Y and then use
> that new pidfd to do X. AFAICT, pidfd capabilities only do something
> when they replace ptrace_may_access and friends for access control.
> Otherwise, they seem purely advisory. Am I missing something?
(Sorry for the late reply. It's kinda busy atm.)
Yes, I think the best option is to explore the possibility to make them
act similar to open(). I'll try to post patches soon.
Christian
next prev parent reply other threads:[~2020-01-14 19:21 UTC|newest]
Thread overview: 26+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-01-10 21:34 [PATCH 0/4] introduce memory hinting API for external process Minchan Kim
2020-01-10 21:34 ` [PATCH 1/4] mm: factor out madvise's core functionality Minchan Kim
2020-01-11 7:37 ` SeongJae Park
2020-01-13 18:11 ` Minchan Kim
2020-01-13 18:22 ` SeongJae Park
2020-01-10 21:34 ` [PATCH 2/4] mm: introduce external memory hinting API Minchan Kim
2020-01-11 7:34 ` SeongJae Park
2020-01-13 18:02 ` Minchan Kim
2020-01-13 8:47 ` Kirill Tkhai
2020-01-13 10:42 ` Christian Brauner
2020-01-13 18:44 ` Minchan Kim
2020-01-13 19:10 ` Christian Brauner
2020-01-13 19:27 ` Daniel Colascione
2020-01-13 20:42 ` Christian Brauner
2020-01-13 21:04 ` Daniel Colascione
2020-01-14 19:20 ` Christian Brauner [this message]
2020-01-14 18:59 ` Minchan Kim
2020-01-14 19:22 ` Christian Brauner
2020-01-13 18:39 ` Minchan Kim
2020-01-13 19:18 ` Daniel Colascione
2020-01-14 8:39 ` Kirill Tkhai
2020-01-14 19:12 ` Minchan Kim
2020-01-15 9:38 ` Kirill Tkhai
2020-01-10 21:34 ` [PATCH 3/4] mm/madvise: employ mmget_still_valid for write lock Minchan Kim
2020-01-10 21:34 ` [PATCH 4/4] mm/madvise: allow KSM hints for remote API Minchan Kim
2020-01-11 7:42 ` SeongJae Park
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