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=-3.7 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED autolearn=no 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 AA44FC47254 for ; Thu, 30 Apr 2020 19:10:43 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 93CE02054F for ; Thu, 30 Apr 2020 19:10:43 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726810AbgD3TKj (ORCPT ); Thu, 30 Apr 2020 15:10:39 -0400 Received: from out01.mta.xmission.com ([166.70.13.231]:58196 "EHLO out01.mta.xmission.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726487AbgD3TKj (ORCPT ); Thu, 30 Apr 2020 15:10:39 -0400 Received: from in01.mta.xmission.com ([166.70.13.51]) by out01.mta.xmission.com with esmtps (TLS1.2:ECDHE_RSA_AES_128_GCM_SHA256:128) (Exim 4.90_1) (envelope-from ) id 1jUEZk-0000zA-Oa; Thu, 30 Apr 2020 13:10:24 -0600 Received: from ip68-227-160-95.om.om.cox.net ([68.227.160.95] helo=x220.xmission.com) by in01.mta.xmission.com with esmtpsa (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.87) (envelope-from ) id 1jUEZj-0004x2-MM; Thu, 30 Apr 2020 13:10:24 -0600 From: ebiederm@xmission.com (Eric W. Biederman) To: Linus Torvalds Cc: Greg Ungerer , Russell King - ARM Linux admin , Jann Horn , Nicolas Pitre , Andrew Morton , Christoph Hellwig , Linux Kernel Mailing List , Linux-MM , linux-fsdevel , Alexander Viro , Oleg Nesterov , Linux ARM , Mark Salter , Aurelien Jacquiot , linux-c6x-dev@linux-c6x.org, Yoshinori Sato , Rich Felker , Linux-sh list References: <20200429214954.44866-1-jannh@google.com> <20200429215620.GM1551@shell.armlinux.org.uk> <31196268-2ff4-7a1d-e9df-6116e92d2190@linux-m68k.org> Date: Thu, 30 Apr 2020 14:07:06 -0500 In-Reply-To: (Linus Torvalds's message of "Thu, 30 Apr 2020 09:54:28 -0700") Message-ID: <87imhgyeqt.fsf@x220.int.ebiederm.org> User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/26.1 (gnu/linux) MIME-Version: 1.0 Content-Type: text/plain X-XM-SPF: eid=1jUEZj-0004x2-MM;;;mid=<87imhgyeqt.fsf@x220.int.ebiederm.org>;;;hst=in01.mta.xmission.com;;;ip=68.227.160.95;;;frm=ebiederm@xmission.com;;;spf=neutral X-XM-AID: U2FsdGVkX1+M59kbFeatkOUeTsajPIqn7fwIqzhVK08= X-SA-Exim-Connect-IP: 68.227.160.95 X-SA-Exim-Mail-From: ebiederm@xmission.com Subject: Re: [PATCH v2 0/5] Fix ELF / FDPIC ELF core dumping, and use mmap_sem properly in there X-SA-Exim-Version: 4.2.1 (built Thu, 05 May 2016 13:38:54 -0600) X-SA-Exim-Scanned: Yes (on in01.mta.xmission.com) Sender: linux-fsdevel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@vger.kernel.org Linus Torvalds writes: > On Thu, Apr 30, 2020 at 7:10 AM Greg Ungerer wrote: >> > Most of that file goes back to pre-git days. And most of the commits >> > since are not so much about binfmt_flat, as they are about cleanups or >> > changes elsewhere where binfmt_flat was just a victim. >> >> I'll have a look at this. > > Thanks. > >> Quick hack test shows moving setup_new_exec(bprm) to be just before >> install_exec_creds(bprm) works fine for the static binaries case. >> Doing the flush_old_exec(bprm) there too crashed out - I'll need to >> dig into that to see why. > > Just moving setup_new_exec() would at least allow us to then join the > two together, and just say "setup_new_exec() does the credential > installation too". But it is only half a help if we allow failure points between flush_old_exec and install_exec_creds. Greg do things work acceptably if install_exec_creds is moved to right after setup_new_exec? (patch below) Looking at the code in load_flat_file after setup_new_exec it looks like the kinds of things that in binfmt_elf.c we do after install_exec_creds (aka vm_map). So I think we want install_exec_creds sooner, instead of setup_new_exec later. > But if it's true that nobody really uses the odd flat library support > any more and there are no testers, maybe we should consider ripping it > out... I looked a little deeper and there is another reason to think about ripping out the flat library loader. The code is recursive, and supports a maximum of 4 shared libraries in the entire system. load_flat_binary load_flat_file calc_reloc load_flat_shared_libary load_flat_file .... I am mystified with what kind of system can survive with a grand total of 4 shared libaries. I think my a.out slackware system that I ran on my i486 had more shared libraries. Having read just a bit more it is definitely guaranteed (by the code) that the first time load_flat_file is called id 0 will be used (aka id 0 is guaranteed to be the binary), and the ids 1, 2, 3 and 4 will only be used if a relocation includes that id to reference an external shared library. That part of the code is drop dead simple. --- This is what I was thinking about applying. diff --git a/fs/binfmt_flat.c b/fs/binfmt_flat.c index 831a2b25ba79..1a1d1fcb893f 100644 --- a/fs/binfmt_flat.c +++ b/fs/binfmt_flat.c @@ -541,6 +541,7 @@ static int load_flat_file(struct linux_binprm *bprm, /* OK, This is the point of no return */ set_personality(PER_LINUX_32BIT); setup_new_exec(bprm); + install_exec_creds(bprm); } /* @@ -963,8 +964,6 @@ static int load_flat_binary(struct linux_binprm *bprm) } } - install_exec_creds(bprm); - set_binfmt(&flat_format); #ifdef CONFIG_MMU