Linux-Fsdevel Archive on lore.kernel.org
help / color / mirror / Atom feed
From: Andy Lutomirski <luto@kernel.org>
To: Stefano Garzarella <sgarzare@redhat.com>,
	Jens Axboe <axboe@kernel.dk>, Christoph Hellwig <hch@lst.de>
Cc: Kees Cook <keescook@chromium.org>,
	Pavel Begunkov <asml.silence@gmail.com>,
	Miklos Szeredi <miklos@szeredi.hu>,
	Matthew Wilcox <willy@infradead.org>,
	Jann Horn <jannh@google.com>,
	Christian Brauner <christian.brauner@ubuntu.com>,
	strace-devel@lists.strace.io, io-uring@vger.kernel.org,
	Linux API <linux-api@vger.kernel.org>,
	Linux FS Devel <linux-fsdevel@vger.kernel.org>,
	LKML <linux-kernel@vger.kernel.org>,
	Michael Kerrisk <mtk.manpages@gmail.com>,
	Stefan Hajnoczi <stefanha@redhat.com>
Subject: Re: strace of io_uring events?
Date: Tue, 21 Jul 2020 08:27:34 -0700	[thread overview]
Message-ID: <CALCETrXSPdiVCgh3h=q7w9RyiKnp-=8jOHoFHX=an0cWqK7bzQ@mail.gmail.com> (raw)
In-Reply-To: <20200717080157.ezxapv7pscbqykhl@steredhat.lan>

On Fri, Jul 17, 2020 at 1:02 AM Stefano Garzarella <sgarzare@redhat.com> wrote:
>
> On Thu, Jul 16, 2020 at 08:12:35AM -0700, Kees Cook wrote:
> > On Thu, Jul 16, 2020 at 03:14:04PM +0200, Stefano Garzarella wrote:

> > access (IIUC) is possible without actually calling any of the io_uring
> > syscalls. Is that correct? A process would receive an fd (via SCM_RIGHTS,
> > pidfd_getfd, or soon seccomp addfd), and then call mmap() on it to gain
> > access to the SQ and CQ, and off it goes? (The only glitch I see is
> > waking up the worker thread?)
>
> It is true only if the io_uring istance is created with SQPOLL flag (not the
> default behaviour and it requires CAP_SYS_ADMIN). In this case the
> kthread is created and you can also set an higher idle time for it, so
> also the waking up syscall can be avoided.

I stared at the io_uring code for a while, and I'm wondering if we're
approaching this the wrong way. It seems to me that most of the
complications here come from the fact that io_uring SQEs don't clearly
belong to any particular security principle.  (We have struct creds,
but we don't really have a task or mm.)  But I'm also not convinced
that io_uring actually supports cross-mm submission except by accident
-- as it stands, unless a user is very careful to only submit SQEs
that don't use user pointers, the results will be unpredictable.
Perhaps we can get away with this:

diff --git a/fs/io_uring.c b/fs/io_uring.c
index 74bc4a04befa..92266f869174 100644
--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -7660,6 +7660,20 @@ SYSCALL_DEFINE6(io_uring_enter, unsigned int,
fd, u32, to_submit,
     if (!percpu_ref_tryget(&ctx->refs))
         goto out_fput;

+    if (unlikely(current->mm != ctx->sqo_mm)) {
+        /*
+         * The mm used to process SQEs will be current->mm or
+         * ctx->sqo_mm depending on which submission path is used.
+         * It's also unclear who is responsible for an SQE submitted
+         * out-of-process from a security and auditing perspective.
+         *
+         * Until a real usecase emerges and there are clear semantics
+         * for out-of-process submission, disallow it.
+         */
+        ret = -EACCES;
+        goto out;
+    }
+
     /*
      * For SQ polling, the thread will do all submissions and completions.
      * Just return the requested submit count, and wake the thread if

If we can do that, then we could bind seccomp-like io_uring filters to
an mm, and we get obvious semantics that ought to cover most of the
bases.

Jens, Christoph?

Stefano, what's your intended usecase for your restriction patchset?

  reply	other threads:[~2020-07-21 15:27 UTC|newest]

Thread overview: 29+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-07-15 11:12 Miklos Szeredi
2020-07-15 14:35 ` Andy Lutomirski
2020-07-15 17:11   ` Matthew Wilcox
2020-07-15 19:42     ` Pavel Begunkov
2020-07-15 20:09       ` Miklos Szeredi
2020-07-15 20:20         ` Pavel Begunkov
2020-07-15 23:07           ` Kees Cook
2020-07-16 13:14             ` Stefano Garzarella
2020-07-16 15:12               ` Kees Cook
2020-07-17  8:01                 ` Stefano Garzarella
2020-07-21 15:27                   ` Andy Lutomirski [this message]
2020-07-21 15:31                     ` Jens Axboe
2020-07-21 17:23                       ` Andy Lutomirski
2020-07-21 17:30                         ` Jens Axboe
2020-07-21 17:44                           ` Andy Lutomirski
2020-07-21 18:39                             ` Jens Axboe
2020-07-21 19:44                               ` Andy Lutomirski
2020-07-21 19:48                                 ` Jens Axboe
2020-07-21 19:56                                 ` Andres Freund
2020-07-21 19:37                         ` Andres Freund
2020-07-21 15:58                     ` Stefano Garzarella
2020-07-23 10:39                       ` Stefan Hajnoczi
2020-07-23 13:37                       ` Colin Walters
2020-07-24  7:25                         ` Stefano Garzarella
2020-07-16 13:17             ` Aleksa Sarai
2020-07-16 15:19               ` Kees Cook
2020-07-17  8:17               ` Cyril Hrubis
2020-07-16 16:24             ` Andy Lutomirski
2020-07-16  0:12     ` tytso

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to='CALCETrXSPdiVCgh3h=q7w9RyiKnp-=8jOHoFHX=an0cWqK7bzQ@mail.gmail.com' \
    --to=luto@kernel.org \
    --cc=asml.silence@gmail.com \
    --cc=axboe@kernel.dk \
    --cc=christian.brauner@ubuntu.com \
    --cc=hch@lst.de \
    --cc=io-uring@vger.kernel.org \
    --cc=jannh@google.com \
    --cc=keescook@chromium.org \
    --cc=linux-api@vger.kernel.org \
    --cc=linux-fsdevel@vger.kernel.org \
    --cc=linux-kernel@vger.kernel.org \
    --cc=miklos@szeredi.hu \
    --cc=mtk.manpages@gmail.com \
    --cc=sgarzare@redhat.com \
    --cc=stefanha@redhat.com \
    --cc=strace-devel@lists.strace.io \
    --cc=willy@infradead.org \
    --subject='Re: strace of io_uring events?' \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link

This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).