From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-7.1 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,INCLUDES_PATCH,MAILING_LIST_MULTI, SPF_HELO_NONE,SPF_PASS autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id DE484C433E6 for ; Tue, 21 Jul 2020 15:27:53 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id B74992077D for ; Tue, 21 Jul 2020 15:27:53 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1595345273; bh=dL7Jw9KmKIYfCmIThtzQuCIzVWDKDKywulNrdIg2buI=; h=References:In-Reply-To:From:Date:Subject:To:Cc:List-ID:From; b=exS4RCK3JZ3EB1PjJzUC4uOMjG8CHhpfPe1bOW6gurm3QvJ6pKODwm240rnqgl0IM o/Uw+Xq0AwlRnjgrjLORkBOtjO4r30mb6bmJb9EgTd3AyQw+YcMy52HSVrN0rwpWD3 Rz4ZJW159yfhbslw82h5Nl5wdwkPsBije4ncHFc8= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729786AbgGUP1u (ORCPT ); Tue, 21 Jul 2020 11:27:50 -0400 Received: from mail.kernel.org ([198.145.29.99]:56542 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728775AbgGUP1t (ORCPT ); Tue, 21 Jul 2020 11:27:49 -0400 Received: from mail-wr1-f52.google.com (mail-wr1-f52.google.com [209.85.221.52]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id C3155206E9 for ; Tue, 21 Jul 2020 15:27:48 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1595345269; bh=dL7Jw9KmKIYfCmIThtzQuCIzVWDKDKywulNrdIg2buI=; h=References:In-Reply-To:From:Date:Subject:To:Cc:From; b=j0qRLvgmYQ9iXUqJ4f4hiZXX+OC7ujiyWP5EZtQyEfF4iDeAt6CeXmdA0V1+otFGZ ePL1Enpmwdgg1XrlRvW3NTB4VJCiZ1CoYTXOS46oM3P/dYP/h46vNrhyvd6fFuYtck gxufNMXrr7yOktk0HDH9GFzFZXNYolk0wn50WmuA= Received: by mail-wr1-f52.google.com with SMTP id r12so21522615wrj.13 for ; Tue, 21 Jul 2020 08:27:48 -0700 (PDT) X-Gm-Message-State: AOAM530BekQkmJnaEyTCJlh4o4BQJcccxWraew8YVnTAs7xtUkpkTyLj GWUi8n5Bm8zpeUxtrq4LU/8tGDbiKVSKmJ55ErSZ5g== X-Google-Smtp-Source: ABdhPJzs/y1/L+ekPbxoouGPVxU+hlgPxvyWi1Ma7ez4YIIKHie9EHhNDAWjrb2H6ZhhYQES2PRhXXKktTgN8DqKT1Y= X-Received: by 2002:a5d:5273:: with SMTP id l19mr17785233wrc.257.1595345267417; Tue, 21 Jul 2020 08:27:47 -0700 (PDT) MIME-Version: 1.0 References: <20200715171130.GG12769@casper.infradead.org> <7c09f6af-653f-db3f-2378-02dca2bc07f7@gmail.com> <48cc7eea-5b28-a584-a66c-4eed3fac5e76@gmail.com> <202007151511.2AA7718@keescook> <20200716131404.bnzsaarooumrp3kx@steredhat> <202007160751.ED56C55@keescook> <20200717080157.ezxapv7pscbqykhl@steredhat.lan> In-Reply-To: <20200717080157.ezxapv7pscbqykhl@steredhat.lan> From: Andy Lutomirski Date: Tue, 21 Jul 2020 08:27:34 -0700 X-Gmail-Original-Message-ID: Message-ID: Subject: Re: strace of io_uring events? To: Stefano Garzarella , Jens Axboe , Christoph Hellwig Cc: Kees Cook , Pavel Begunkov , Miklos Szeredi , Matthew Wilcox , Jann Horn , Christian Brauner , strace-devel@lists.strace.io, io-uring@vger.kernel.org, Linux API , Linux FS Devel , LKML , Michael Kerrisk , Stefan Hajnoczi Content-Type: text/plain; charset="UTF-8" Sender: io-uring-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: io-uring@vger.kernel.org On Fri, Jul 17, 2020 at 1:02 AM Stefano Garzarella 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?