From patchwork Wed Aug 16 17:55:51 2023 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Jeff Moyer X-Patchwork-Id: 13355520 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 179B4C001B0 for ; Wed, 16 Aug 2023 17:51:51 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1345139AbjHPRvT (ORCPT ); Wed, 16 Aug 2023 13:51:19 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:53106 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S236917AbjHPRuw (ORCPT ); Wed, 16 Aug 2023 13:50:52 -0400 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.133.124]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id C35412705 for ; Wed, 16 Aug 2023 10:50:13 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1692208213; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type; bh=OgS5/8uGly2sniToh80UD20m9zUfkHMdpXbITA9PzKk=; b=fxq5Si1JnXEzjOFMexlFTcLEReY3SokcCMsMAYiK6q8SzouafkqvKEU9E6BxPwnNNqEvve NRsYAi78oRH3IV03a456Bed2mQrVgINSuOZG1HOp2hP4jVdH+CP1dphvNC8VAbry5GdC2A rPj0C59Jpp1nfVP16M2mEPayAoU34q8= Received: from mimecast-mx02.redhat.com (66.187.233.73 [66.187.233.73]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-686-Vqwh6lMyOBK_tjCvJ3FZYQ-1; Wed, 16 Aug 2023 13:50:06 -0400 X-MC-Unique: Vqwh6lMyOBK_tjCvJ3FZYQ-1 Received: from smtp.corp.redhat.com (int-mx02.intmail.prod.int.rdu2.redhat.com [10.11.54.2]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id 893C1381494C; Wed, 16 Aug 2023 17:50:05 +0000 (UTC) Received: from segfault.boston.devel.redhat.com (segfault.boston.devel.redhat.com [10.19.60.26]) by smtp.corp.redhat.com (Postfix) with ESMTPS id D35894094DC0; Wed, 16 Aug 2023 17:50:04 +0000 (UTC) From: Jeff Moyer To: matteorizzo@google.com, linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, io-uring@vger.kernel.org, axboe@kernel.dk, asml.silence@gmail.com Cc: corbet@lwn.net, akpm@linux-foundation.org, keescook@chromium.org, ribalda@chromium.org, rostedt@goodmis.org, jannh@google.com, chenhuacai@kernel.org, gpiccoli@igalia.com, ldufour@linux.ibm.com, evn@google.com, poprdi@google.com, jordyzomer@google.com, krisman@suse.de, andres@anarazel.de Subject: [PATCH v4] io_uring: add a sysctl to disable io_uring system-wide X-PGP-KeyID: 1F78E1B4 X-PGP-CertKey: F6FE 280D 8293 F72C 65FD 5A58 1FF8 A7CA 1F78 E1B4 Date: Wed, 16 Aug 2023 13:55:51 -0400 Message-ID: User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/26.1 (gnu/linux) MIME-Version: 1.0 X-Scanned-By: MIMEDefang 3.1 on 10.11.54.2 Precedence: bulk List-ID: X-Mailing-List: io-uring@vger.kernel.org From: Matteo Rizzo Introduce a new sysctl (io_uring_disabled) which can be either 0, 1, or 2. When 0 (the default), all processes are allowed to create io_uring instances, which is the current behavior. When 1, io_uring creation is disabled (io_uring_setup() will fail with -EPERM) for processes not in the kernel.io_uring_group group. When 2, calls to io_uring_setup() fail with -EPERM regardless of privilege. Signed-off-by: Matteo Rizzo [JEM: modified to add io_uring_group] Signed-off-by: Jeff Moyer --- v4: * Add a kernel.io_uring_group sysctl to hold a group id that is allowed to use io_uring. One thing worth pointing out is that, when a group is specified, only users in that group can create an io_uring. That means that if the root user is not in that group, root can not make use of io_uring. I also wrote unit tests for liburing. I'll post that as well if there is consensus on this approach. Matteo, you didn't reply to Jens' message about pulling the patch, so I figured you got busy, so I picked up the patch. I hope you're okay with the signoff. v3: * Fix the commit message * Use READ_ONCE in io_uring_allowed to avoid races * Add reviews v2: * Documentation style fixes * Add a third level that only disables io_uring for unprivileged processes diff --git a/Documentation/admin-guide/sysctl/kernel.rst b/Documentation/admin-guide/sysctl/kernel.rst index 3800fab1619b..dc4b19f2f2cb 100644 --- a/Documentation/admin-guide/sysctl/kernel.rst +++ b/Documentation/admin-guide/sysctl/kernel.rst @@ -450,6 +450,34 @@ this allows system administrators to override the ``IA64_THREAD_UAC_NOPRINT`` ``prctl`` and avoid logs being flooded. +io_uring_disabled +================= + +Prevents all processes from creating new io_uring instances. Enabling this +shrinks the kernel's attack surface. + += ====================================================================== +0 All processes can create io_uring instances as normal. This is the + default setting. +1 io_uring creation is disabled (io_uring_setup() will fail with -EPERM) + for processes not in the io_uring_group group. Existing io_uring + instances can still be used. See the documentation for io_uring_group + for more information. +2 io_uring creation is disabled for all processes. io_uring_setup() + always fails with -EPERM. Existing io_uring instances can still be + used. += ====================================================================== + + +io_uring_group +============== + +When io_uring_disabled is set to 1, a process must be in the +io_uring_group group in order to create an io_uring instance. If +io_uring_group is set to -1 (the default), only processes with the +CAP_SYS_ADMIN capability may create io_uring instances. + + kexec_load_disabled =================== diff --git a/io_uring/io_uring.c b/io_uring/io_uring.c index 93db3e4e7b68..fbee37fb9bad 100644 --- a/io_uring/io_uring.c +++ b/io_uring/io_uring.c @@ -152,6 +152,31 @@ static void __io_submit_flush_completions(struct io_ring_ctx *ctx); struct kmem_cache *req_cachep; +static int __read_mostly sysctl_io_uring_disabled; +static int __read_mostly sysctl_io_uring_group = -1; + +#ifdef CONFIG_SYSCTL +static struct ctl_table kernel_io_uring_disabled_table[] = { + { + .procname = "io_uring_disabled", + .data = &sysctl_io_uring_disabled, + .maxlen = sizeof(sysctl_io_uring_disabled), + .mode = 0644, + .proc_handler = proc_dointvec_minmax, + .extra1 = SYSCTL_ZERO, + .extra2 = SYSCTL_TWO, + }, + { + .procname = "io_uring_group", + .data = &sysctl_io_uring_group, + .maxlen = sizeof(gid_t), + .mode = 0644, + .proc_handler = proc_dointvec, + }, + {}, +}; +#endif + struct sock *io_uring_get_socket(struct file *file) { #if defined(CONFIG_UNIX) @@ -4040,9 +4065,31 @@ static long io_uring_setup(u32 entries, struct io_uring_params __user *params) return io_uring_create(entries, &p, params); } +static inline bool io_uring_allowed(void) +{ + int disabled = READ_ONCE(sysctl_io_uring_disabled); + kgid_t io_uring_group; + + if (disabled == 0) + return true; + + if (disabled == 2) + return false; + + /* default to root only */ + io_uring_group = make_kgid(&init_user_ns, sysctl_io_uring_group); + if (!gid_valid(io_uring_group)) + return capable(CAP_SYS_ADMIN); + + return in_group_p(io_uring_group); +} + SYSCALL_DEFINE2(io_uring_setup, u32, entries, struct io_uring_params __user *, params) { + if (!io_uring_allowed()) + return -EPERM; + return io_uring_setup(entries, params); } @@ -4617,6 +4664,11 @@ static int __init io_uring_init(void) req_cachep = KMEM_CACHE(io_kiocb, SLAB_HWCACHE_ALIGN | SLAB_PANIC | SLAB_ACCOUNT | SLAB_TYPESAFE_BY_RCU); + +#ifdef CONFIG_SYSCTL + register_sysctl_init("kernel", kernel_io_uring_disabled_table); +#endif + return 0; }; __initcall(io_uring_init);