From nobody Fri Oct 17 10:32:13 2025 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 9EA26C433FE for ; Wed, 19 Oct 2022 10:47:42 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S233727AbiJSKrk (ORCPT ); Wed, 19 Oct 2022 06:47:40 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:49162 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S232801AbiJSKp1 (ORCPT ); Wed, 19 Oct 2022 06:45:27 -0400 Received: from ams.source.kernel.org (ams.source.kernel.org [IPv6:2604:1380:4601:e00::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 3D38E26AF7; Wed, 19 Oct 2022 03:21:32 -0700 (PDT) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by ams.source.kernel.org (Postfix) with ESMTPS id F3E36B82304; Wed, 19 Oct 2022 08:47:14 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 4ED99C433C1; Wed, 19 Oct 2022 08:47:13 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1666169233; bh=NNlN43yRYP/GS1meNtY2/HGKhqpVXSar/Y/KnVaTkSA=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=tqKdZp3u/pujysaXeK19W8Y6rXPWUg8vUOpi4LM4JllX5UtheOR5vDqMVC0HGpaRn l4kvToE1sIMcSM8jACVHntCgqHBRth2Sk+si3gavR/BkgAvVFU4AsLk6B6j1YvNnvM f5hg69YqBKVVSo9LTcGIgLwi4pEzFv/XuvdUBfh0= From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Robert OCallahan , Ondrej Mosnacek , Peter Xu , "Christian Brauner (Microsoft)" , Paul Moore , Sasha Levin Subject: [PATCH 6.0 204/862] userfaultfd: open userfaultfds with O_RDONLY Date: Wed, 19 Oct 2022 10:24:51 +0200 Message-Id: <20221019083259.023119499@linuxfoundation.org> X-Mailer: git-send-email 2.38.0 In-Reply-To: <20221019083249.951566199@linuxfoundation.org> References: <20221019083249.951566199@linuxfoundation.org> User-Agent: quilt/0.67 MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Type: text/plain; charset="utf-8" From: Ondrej Mosnacek [ Upstream commit abec3d015fdfb7c63105c7e1c956188bf381aa55 ] Since userfaultfd doesn't implement a write operation, it is more appropriate to open it read-only. When userfaultfds are opened read-write like it is now, and such fd is passed from one process to another, SELinux will check both read and write permissions for the target process, even though it can't actually do any write operation on the fd later. Inspired by the following bug report, which has hit the SELinux scenario described above: https://bugzilla.redhat.com/show_bug.cgi?id=3D1974559 Reported-by: Robert O'Callahan Fixes: 86039bd3b4e6 ("userfaultfd: add new syscall to provide memory extern= alization") Signed-off-by: Ondrej Mosnacek Acked-by: Peter Xu Acked-by: Christian Brauner (Microsoft) Signed-off-by: Paul Moore Signed-off-by: Sasha Levin --- fs/userfaultfd.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) diff --git a/fs/userfaultfd.c b/fs/userfaultfd.c index 175de70e3adf..0c1d33c4f74c 100644 --- a/fs/userfaultfd.c +++ b/fs/userfaultfd.c @@ -991,7 +991,7 @@ static int resolve_userfault_fork(struct userfaultfd_ct= x *new, int fd; =20 fd =3D anon_inode_getfd_secure("[userfaultfd]", &userfaultfd_fops, new, - O_RDWR | (new->flags & UFFD_SHARED_FCNTL_FLAGS), inode); + O_RDONLY | (new->flags & UFFD_SHARED_FCNTL_FLAGS), inode); if (fd < 0) return fd; =20 @@ -2094,7 +2094,7 @@ SYSCALL_DEFINE1(userfaultfd, int, flags) mmgrab(ctx->mm); =20 fd =3D anon_inode_getfd_secure("[userfaultfd]", &userfaultfd_fops, ctx, - O_RDWR | (flags & UFFD_SHARED_FCNTL_FLAGS), NULL); + O_RDONLY | (flags & UFFD_SHARED_FCNTL_FLAGS), NULL); if (fd < 0) { mmdrop(ctx->mm); kmem_cache_free(userfaultfd_ctx_cachep, ctx); --=20 2.35.1