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=-6.8 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SIGNED_OFF_BY, SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_GIT 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 8607EC433FF for ; Fri, 2 Aug 2019 09:44:25 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 5D0DB21726 for ; Fri, 2 Aug 2019 09:44:25 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1564739065; bh=aE+CR6HoZfXk0nsZLEeNWPnKxJ0ykrIP8FUejcRW7KY=; h=From:To:Cc:Subject:Date:In-Reply-To:References:List-ID:From; b=Ng7a/wl/3aVeKVueKuyM0SsfcWXvtupPk61BzTSOHoRp3ZvxwgJLi/qz6b8AsgP0v pQI+Le9oUn883Ldw6fdl2sBGWBGec+w3x76QkJHYrR0eyEexquvEXG+mVd2yTxKDKW E1om0JBrgVaz8MPG1tDQl2AK8I3SbSyxvtrmJoAs= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2404861AbfHBJoY (ORCPT ); Fri, 2 Aug 2019 05:44:24 -0400 Received: from mail.kernel.org ([198.145.29.99]:47658 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2405217AbfHBJoS (ORCPT ); Fri, 2 Aug 2019 05:44:18 -0400 Received: from localhost (83-86-89-107.cable.dynamic.v4.ziggo.nl [83.86.89.107]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id D0FB12086A; Fri, 2 Aug 2019 09:44:16 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1564739057; bh=aE+CR6HoZfXk0nsZLEeNWPnKxJ0ykrIP8FUejcRW7KY=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=iZ/Ty4D6jJeXVcPdATJRHospV0Nea037XXsd2E8kBsD20V3YNi1EG6gZB8fnjd76X V0K/8oiZCexbwbk6v1wOZSCxR20AgA11ANEffeg39ayizoWwyeO/pVrbLIGg4k6Qo6 IYVCWeM3bLaO2JVq00q8g6aI2cl2odG6jFyezsL8= From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Radoslaw Burny , Luis Chamberlain , Kees Cook , "Eric W . Biederman" , Seth Forshee , John Sperbeck , Alexey Dobriyan , Andrew Morton , Linus Torvalds Subject: [PATCH 4.9 096/223] fs/proc/proc_sysctl.c: fix the default values of i_uid/i_gid on /proc/sys inodes. Date: Fri, 2 Aug 2019 11:35:21 +0200 Message-Id: <20190802092245.395264338@linuxfoundation.org> X-Mailer: git-send-email 2.22.0 In-Reply-To: <20190802092238.692035242@linuxfoundation.org> References: <20190802092238.692035242@linuxfoundation.org> User-Agent: quilt/0.66 MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Radoslaw Burny commit 5ec27ec735ba0477d48c80561cc5e856f0c5dfaf upstream. Normally, the inode's i_uid/i_gid are translated relative to s_user_ns, but this is not a correct behavior for proc. Since sysctl permission check in test_perm is done against GLOBAL_ROOT_[UG]ID, it makes more sense to use these values in u_[ug]id of proc inodes. In other words: although uid/gid in the inode is not read during test_perm, the inode logically belongs to the root of the namespace. I have confirmed this with Eric Biederman at LPC and in this thread: https://lore.kernel.org/lkml/87k1kzjdff.fsf@xmission.com Consequences ============ Since the i_[ug]id values of proc nodes are not used for permissions checks, this change usually makes no functional difference. However, it causes an issue in a setup where: * a namespace container is created without root user in container - hence the i_[ug]id of proc nodes are set to INVALID_[UG]ID * container creator tries to configure it by writing /proc/sys files, e.g. writing /proc/sys/kernel/shmmax to configure shared memory limit Kernel does not allow to open an inode for writing if its i_[ug]id are invalid, making it impossible to write shmmax and thus - configure the container. Using a container with no root mapping is apparently rare, but we do use this configuration at Google. Also, we use a generic tool to configure the container limits, and the inability to write any of them causes a failure. History ======= The invalid uids/gids in inodes first appeared due to 81754357770e (fs: Update i_[ug]id_(read|write) to translate relative to s_user_ns). However, AFAIK, this did not immediately cause any issues. The inability to write to these "invalid" inodes was only caused by a later commit 0bd23d09b874 (vfs: Don't modify inodes with a uid or gid unknown to the vfs). Tested: Used a repro program that creates a user namespace without any mapping and stat'ed /proc/$PID/root/proc/sys/kernel/shmmax from outside. Before the change, it shows the overflow uid, with the change it's 0. The overflow uid indicates that the uid in the inode is not correct and thus it is not possible to open the file for writing. Link: http://lkml.kernel.org/r/20190708115130.250149-1-rburny@google.com Fixes: 0bd23d09b874 ("vfs: Don't modify inodes with a uid or gid unknown to the vfs") Signed-off-by: Radoslaw Burny Acked-by: Luis Chamberlain Cc: Kees Cook Cc: "Eric W . Biederman" Cc: Seth Forshee Cc: John Sperbeck Cc: Alexey Dobriyan Cc: [4.8+] Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds Signed-off-by: Greg Kroah-Hartman --- fs/proc/proc_sysctl.c | 4 ++++ 1 file changed, 4 insertions(+) --- a/fs/proc/proc_sysctl.c +++ b/fs/proc/proc_sysctl.c @@ -500,6 +500,10 @@ static struct inode *proc_sys_make_inode if (root->set_ownership) root->set_ownership(head, table, &inode->i_uid, &inode->i_gid); + else { + inode->i_uid = GLOBAL_ROOT_UID; + inode->i_gid = GLOBAL_ROOT_GID; + } return inode; }