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 DFE8AECAAA1 for ; Fri, 9 Sep 2022 10:06:46 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229976AbiIIKGp convert rfc822-to-8bit (ORCPT ); Fri, 9 Sep 2022 06:06:45 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:51008 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229962AbiIIKGj (ORCPT ); Fri, 9 Sep 2022 06:06:39 -0400 Received: from eu-smtp-delivery-151.mimecast.com (eu-smtp-delivery-151.mimecast.com [185.58.86.151]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 0D908B03 for ; Fri, 9 Sep 2022 03:06:36 -0700 (PDT) Received: from AcuMS.aculab.com (156.67.243.121 [156.67.243.121]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_CBC_SHA384) id uk-mta-135-vA_9hz_UMB--kDxjteYY_w-1; Fri, 09 Sep 2022 11:06:34 +0100 X-MC-Unique: vA_9hz_UMB--kDxjteYY_w-1 Received: from AcuMS.Aculab.com (10.202.163.4) by AcuMS.aculab.com (10.202.163.4) with Microsoft SMTP Server (TLS) id 15.0.1497.38; Fri, 9 Sep 2022 11:06:32 +0100 Received: from AcuMS.Aculab.com ([::1]) by AcuMS.aculab.com ([::1]) with mapi id 15.00.1497.040; Fri, 9 Sep 2022 11:06:32 +0100 From: David Laight To: "'adobriyan@gmail.com'" CC: "linux-kernel@vger.kernel.org" Subject: procfs readlink after unshare() in a chroot() reports the full path Thread-Topic: procfs readlink after unshare() in a chroot() reports the full path Thread-Index: AdjEMqjMb0GR/+CiSFubzc4Cg1EybA== Date: Fri, 9 Sep 2022 10:06:32 +0000 Message-ID: <12add75b103b412494487518c408fe0b@AcuMS.aculab.com> Accept-Language: en-GB, en-US X-MS-Has-Attach: X-MS-TNEF-Correlator: x-ms-exchange-transport-fromentityheader: Hosted x-originating-ip: [10.202.205.107] MIME-Version: 1.0 X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: aculab.com Content-Language: en-US Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8BIT Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org The readlink calls in procfs (eg for /proc/self/fd/0) returns the full pathname if unshare() is called inside a chroot. The program below reproduces this when run with stdin redirected to a file in the current directory. This sequence is used by 'ip netns exec' so isn't actually that unusual. David #define _GNU_SOURCE #include #include #include #include static void print_link(const char *where, int fd) { char buf[256]; printf("%s: %.*s\n", where, (int)readlinkat(fd, "", buf, sizeof buf), buf); } int main(int argc, char **argv) { int link_fd = open("/proc/self/fd/0", O_PATH | O_NOFOLLOW); print_link("initial", link_fd); if (chroot(".")) return 1; print_link("after chroot", link_fd); if (unshare(CLONE_NEWNS)) return 2; print_link("after unshare", link_fd); return 0; } - Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK Registration No: 1397386 (Wales)