From nobody Fri Dec 19 18:53:19 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 45A07C38A2D for ; Mon, 24 Oct 2022 13:06:28 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S235415AbiJXNG0 (ORCPT ); Mon, 24 Oct 2022 09:06:26 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:49720 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S235372AbiJXNEj (ORCPT ); Mon, 24 Oct 2022 09:04:39 -0400 Received: from dfw.source.kernel.org (dfw.source.kernel.org [IPv6:2604:1380:4641:c500::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 72BC74D4F2; Mon, 24 Oct 2022 05:20:21 -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 dfw.source.kernel.org (Postfix) with ESMTPS id 5E8A66129D; Mon, 24 Oct 2022 12:19:53 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 735A3C433D6; Mon, 24 Oct 2022 12:19:52 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1666613992; bh=hn6W96T8z04EogJtNH5PSoub5gNDEco86kNA8E7waSg=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=uf3ORQ4dFYf2jalbFOn8wQ1Jkl+jTLa/Q6KS96IdeKWQuRyEHqFzCPdsnZnmYbI6R zRS0Dm58loifcCRkHEhLqgKKu6OcmkSr6RwbJY11f5i+fOUsc7fU4rfzRX1tEjTgND yj9iBvIld/xhVKKj0s5Gwr5/wl6pFSEzEj6IXTX4= 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 5.10 092/390] userfaultfd: open userfaultfds with O_RDONLY Date: Mon, 24 Oct 2022 13:28:09 +0200 Message-Id: <20221024113026.545715262@linuxfoundation.org> X-Mailer: git-send-email 2.38.1 In-Reply-To: <20221024113022.510008560@linuxfoundation.org> References: <20221024113022.510008560@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 aef0da5d6f63..a3074a9d71a6 100644 --- a/fs/userfaultfd.c +++ b/fs/userfaultfd.c @@ -974,7 +974,7 @@ static int resolve_userfault_fork(struct userfaultfd_ct= x *ctx, int fd; =20 fd =3D 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; =20 @@ -1987,7 +1987,7 @@ SYSCALL_DEFINE1(userfaultfd, int, flags) mmgrab(ctx->mm); =20 fd =3D 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); --=20 2.35.1