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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id E6E19C38A2D for ; Mon, 24 Oct 2022 20:56:24 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S234907AbiJXU4X (ORCPT ); Mon, 24 Oct 2022 16:56:23 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:50810 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S232571AbiJXU4C (ORCPT ); Mon, 24 Oct 2022 16:56:02 -0400 Received: from ams.source.kernel.org (ams.source.kernel.org [145.40.68.75]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id E600F2413CA; Mon, 24 Oct 2022 12:02:22 -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 759A5B81330; Mon, 24 Oct 2022 12:08:32 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id C4BB6C433D7; Mon, 24 Oct 2022 12:08:30 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1666613311; bh=QOy3cjI1C0pLjk5Kou9W52sE41We3XgJT9GQSvfzZZ4=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=rFs6R6hFdr54lQ59ZL1Q+Pex0r8aByLmHA1QoHbklt4VdzvTjEhL/cJlkEHV51qgA EJAIlCtmCGpJ+D3MsWr+vt5TJhKdVETKIiZlMdnOqX1Rm8K5tiVXSlLCMGCjWUyh6n +RP1YsfK6al72p4i56IDZQ3JJZaiIXWYx0fPISkU= 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 5.4 059/255] userfaultfd: open userfaultfds with O_RDONLY Date: Mon, 24 Oct 2022 13:29:29 +0200 Message-Id: <20221024113004.455015344@linuxfoundation.org> X-Mailer: git-send-email 2.38.1 In-Reply-To: <20221024113002.471093005@linuxfoundation.org> References: <20221024113002.471093005@linuxfoundation.org> User-Agent: quilt/0.67 MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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=1974559 Reported-by: Robert O'Callahan Fixes: 86039bd3b4e6 ("userfaultfd: add new syscall to provide memory externalization") 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 ec57bbb6bb05..740853465356 100644 --- a/fs/userfaultfd.c +++ b/fs/userfaultfd.c @@ -1018,7 +1018,7 @@ static int resolve_userfault_fork(struct userfaultfd_ctx *ctx, int fd; fd = anon_inode_getfd("[userfaultfd]", &userfaultfd_fops, new, - O_RDWR | (new->flags & UFFD_SHARED_FCNTL_FLAGS)); + O_RDONLY | (new->flags & UFFD_SHARED_FCNTL_FLAGS)); if (fd < 0) return fd; @@ -1969,7 +1969,7 @@ SYSCALL_DEFINE1(userfaultfd, int, flags) mmgrab(ctx->mm); fd = anon_inode_getfd("[userfaultfd]", &userfaultfd_fops, ctx, - O_RDWR | (flags & UFFD_SHARED_FCNTL_FLAGS)); + O_RDONLY | (flags & UFFD_SHARED_FCNTL_FLAGS)); if (fd < 0) { mmdrop(ctx->mm); kmem_cache_free(userfaultfd_ctx_cachep, ctx); -- 2.35.1