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=-8.5 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED,USER_AGENT_SANE_1 autolearn=ham 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 70E90C49ED9 for ; Tue, 10 Sep 2019 17:59:24 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 521B821479 for ; Tue, 10 Sep 2019 17:59:24 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728440AbfIJR7X (ORCPT ); Tue, 10 Sep 2019 13:59:23 -0400 Received: from mx1.redhat.com ([209.132.183.28]:48424 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726524AbfIJR7X (ORCPT ); Tue, 10 Sep 2019 13:59:23 -0400 Received: from smtp.corp.redhat.com (int-mx02.intmail.prod.int.phx2.redhat.com [10.5.11.12]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id BE1CA10CC207; Tue, 10 Sep 2019 17:59:22 +0000 (UTC) Received: from asgard.redhat.com (ovpn-112-20.ams2.redhat.com [10.36.112.20]) by smtp.corp.redhat.com (Postfix) with ESMTPS id C640260BF7; Tue, 10 Sep 2019 17:59:17 +0000 (UTC) Date: Tue, 10 Sep 2019 18:58:52 +0100 From: Eugene Syromiatnikov To: linux-kernel@vger.kernel.org, Christian Brauner , Oleg Nesterov Cc: Andrew Morton , "Peter Zijlstra (Intel)" , Ingo Molnar , "Dmitry V. Levin" , Eric Biederman Subject: [PATCH v2] fork: check exit_signal passed in clone3() call Message-ID: <20190910175852.GA15572@asgard.redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline User-Agent: Mutt/1.5.23 (2014-03-12) X-Scanned-By: MIMEDefang 2.79 on 10.5.11.12 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.6.2 (mx1.redhat.com [10.5.110.65]); Tue, 10 Sep 2019 17:59:22 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Previously, higher 32 bits of exit_signal fields were lost when copied to the kernel args structure (that uses int as a type for the respective field). Moreover, as Oleg has noted[1], exit_signal is used unchecked, so it has to be checked for sanity before use; for the legacy syscalls, applying CSIGNAL mask guarantees that it is at least non-negative; however, there's no such thing is done in clone3() code path, and that can break at least thread_group_leader. Checking user-passed exit_signal against ~CSIGNAL mask solves both of these problems. [1] https://lkml.org/lkml/2019/9/10/467 * kernel/fork.c (copy_clone_args_from_user): Fail with -EINVAL if args.exit_signal has bits set outside CSIGNAL mask. (_do_fork): Note that exit_signal is expected to be checked for the sanity by the caller. Fixes: 7f192e3cd316 ("fork: add clone3") Reported-by: Oleg Nesterov Signed-off-by: Eugene Syromiatnikov --- kernel/fork.c | 12 ++++++++++++ 1 file changed, 12 insertions(+) diff --git a/kernel/fork.c b/kernel/fork.c index 2852d0e..9dee2ab 100644 --- a/kernel/fork.c +++ b/kernel/fork.c @@ -2338,6 +2338,8 @@ struct mm_struct *copy_init_mm(void) * * It copies the process, and if successful kick-starts * it and waits for it to finish using the VM if required. + * + * args->exit_signal is expected to be checked for sanity by the caller. */ long _do_fork(struct kernel_clone_args *args) { @@ -2562,6 +2564,16 @@ noinline static int copy_clone_args_from_user(struct kernel_clone_args *kargs, if (copy_from_user(&args, uargs, size)) return -EFAULT; + /* + * exit_signal is confined to CSIGNAL mask in legacy syscalls, + * so it is used unchecked deeper in syscall handling routines; + * moreover, copying to struct kernel_clone_args.exit_signals + * trims higher 32 bits, so it is has to be checked that they + * are zero. + */ + if (unlikely(args.exit_signal & ~((u64)CSIGNAL))) + return -EINVAL; + *kargs = (struct kernel_clone_args){ .flags = args.flags, .pidfd = u64_to_user_ptr(args.pidfd), -- 2.1.4