From: Christian Brauner <[email protected]>
To: Jens Axboe <[email protected]>
Cc: Pavel Begunkov <[email protected]>,
Stefan Metzmacher <[email protected]>,
io-uring <[email protected]>,
Linux API Mailing List <[email protected]>
Subject: Re: IORING_REGISTER_CREDS[_UPDATE]() and credfd_create()?
Date: Tue, 28 Jan 2020 22:25:33 +0100 [thread overview]
Message-ID: <20200128212533.snjm34gct3kmfxfi@wittgenstein> (raw)
In-Reply-To: <[email protected]>
On Tue, Jan 28, 2020 at 01:56:00PM -0700, Jens Axboe wrote:
> On 1/28/20 1:50 PM, Pavel Begunkov wrote:
> > On 28/01/2020 23:19, Jens Axboe wrote:
> >> On 1/28/20 1:16 PM, Pavel Begunkov wrote:
> >>> On 28/01/2020 22:42, Jens Axboe wrote:
> >>>> On 1/28/20 11:04 AM, Jens Axboe wrote:
> >>>>> On 1/28/20 10:19 AM, Jens Axboe wrote:
> >>>>>> On 1/28/20 9:19 AM, Jens Axboe wrote:
> >>>>>>> On 1/28/20 9:17 AM, Stefan Metzmacher wrote:
> >>>>>> OK, so here are two patches for testing:
> >>>>>>
> >>>>>> https://git.kernel.dk/cgit/linux-block/log/?h=for-5.6/io_uring-vfs-creds
> >>>>>>
> >>>>>> #1 adds support for registering the personality of the invoking task,
> >>>>>> and #2 adds support for IORING_OP_USE_CREDS. Right now it's limited to
> >>>>>> just having one link, it doesn't support a chain of them.
> >>>>>>
> >>>>>> I'll try and write a test case for this just to see if it actually works,
> >>>>>> so far it's totally untested.
> >>>>>>
> >>>>>> Adding Pavel to the CC.
> >>>>>
> >>>>> Minor tweak to ensuring we do the right thing for async offload as well,
> >>>>> and it tests fine for me. Test case is:
> >>>>>
> >>>>> - Run as root
> >>>>> - Register personality for root
> >>>>> - create root only file
> >>>>> - check we can IORING_OP_OPENAT the file
> >>>>> - switch to user id test
> >>>>> - check we cannot IORING_OP_OPENAT the file
> >>>>> - check that we can open the file with IORING_OP_USE_CREDS linked
> >>>>
> >>>> I didn't like it becoming a bit too complicated, both in terms of
> >>>> implementation and use. And the fact that we'd have to jump through
> >>>> hoops to make this work for a full chain.
> >>>>
> >>>> So I punted and just added sqe->personality and IOSQE_PERSONALITY.
> >>>> This makes it way easier to use. Same branch:
> >>>>
> >>>> https://git.kernel.dk/cgit/linux-block/log/?h=for-5.6/io_uring-vfs-creds
> >>>>
> >>>> I'd feel much better with this variant for 5.6.
> >>>>
> >>>
> >>> To be honest, sounds pretty dangerous. Especially since somebody started talking
> >>> about stealing fds from a process, it could lead to a nasty loophole somehow.
> >>> E.g. root registers its credentials, passes io_uring it to non-privileged
> >>> children, and then some process steals the uring fd (though, it would need
> >>> priviledged mode for code-injection or else). Could we Cc here someone really
> >>> keen on security?
> >>
> >> Link? If you can steal fds, then surely you've already lost any sense of
> >
> > https://lwn.net/Articles/808997/
> > But I didn't looked up it yet.
>
> This isn't new by any stretch, it's always been possible to pass file
> descriptors through SCM_RIGHTS. This just gives you a new way to do it.
> That's not stealing or leaking, it's deliberately passing it to someone
> else.
I've been reading along quietly. In addition to what Jens said, to ease
everyone's mind: pidfd_getfd() doesn't allow to unconditionally grab
file descriptors for any task. That would be crazy. The calling task
needs ptrace_may_access() permissions on the target task, i.e. the task
from which you want to grab the io_uring file descriptor. And any
calling task that has ptrace_may_access() permissions on the target can
do much worse than just grabbing an fd.
Christian
next prev parent reply other threads:[~2020-01-28 21:27 UTC|newest]
Thread overview: 48+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-01-28 10:18 IORING_REGISTER_CREDS[_UPDATE]() and credfd_create()? Stefan Metzmacher
2020-01-28 16:10 ` Jens Axboe
2020-01-28 16:17 ` Stefan Metzmacher
2020-01-28 16:19 ` Jens Axboe
2020-01-28 17:19 ` Jens Axboe
2020-01-28 18:04 ` Jens Axboe
2020-01-28 19:42 ` Jens Axboe
2020-01-28 20:16 ` Pavel Begunkov
2020-01-28 20:19 ` Jens Axboe
2020-01-28 20:50 ` Pavel Begunkov
2020-01-28 20:56 ` Jens Axboe
2020-01-28 21:25 ` Christian Brauner [this message]
2020-01-28 22:38 ` Pavel Begunkov
2020-01-28 23:36 ` Pavel Begunkov
2020-01-28 23:40 ` Jens Axboe
2020-01-28 23:51 ` Jens Axboe
2020-01-29 0:10 ` Pavel Begunkov
2020-01-29 0:15 ` Jens Axboe
2020-01-29 0:18 ` Jens Axboe
2020-01-29 0:20 ` Jens Axboe
2020-01-29 0:21 ` Pavel Begunkov
2020-01-29 0:24 ` Jens Axboe
2020-01-29 0:54 ` Jens Axboe
2020-01-29 10:17 ` Pavel Begunkov
2020-01-29 13:11 ` Stefan Metzmacher
2020-01-29 13:41 ` Pavel Begunkov
2020-01-29 13:56 ` Stefan Metzmacher
2020-01-29 14:23 ` Pavel Begunkov
2020-01-29 14:27 ` Stefan Metzmacher
2020-01-29 14:34 ` Pavel Begunkov
2020-01-29 17:34 ` Jens Axboe
2020-01-29 17:42 ` Jens Axboe
2020-01-29 20:09 ` Stefan Metzmacher
2020-01-29 20:48 ` Jens Axboe
2020-01-29 17:46 ` Pavel Begunkov
2020-01-29 14:59 ` Jann Horn
2020-01-29 17:34 ` Jens Axboe
2020-01-30 1:08 ` Jens Axboe
2020-01-30 2:20 ` Jens Axboe
2020-01-30 3:18 ` Jens Axboe
2020-01-30 6:53 ` Stefan Metzmacher
2020-01-30 10:11 ` Jann Horn
2020-01-30 10:26 ` Christian Brauner
2020-01-30 14:11 ` Jens Axboe
2020-01-30 14:47 ` Stefan Metzmacher
2020-01-30 15:34 ` Jens Axboe
2020-01-30 15:13 ` Christian Brauner
2020-01-30 15:29 ` Jens Axboe
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