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 mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 9D630C43219 for ; Mon, 1 Nov 2021 16:02:19 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 85990610D2 for ; Mon, 1 Nov 2021 16:02:19 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232618AbhKAQEv (ORCPT ); Mon, 1 Nov 2021 12:04:51 -0400 Received: from smtp-out2.suse.de ([195.135.220.29]:52004 "EHLO smtp-out2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230517AbhKAQEt (ORCPT ); Mon, 1 Nov 2021 12:04:49 -0400 Received: from relay2.suse.de (relay2.suse.de [149.44.160.134]) by smtp-out2.suse.de (Postfix) with ESMTP id C0B9C1FD45; Mon, 1 Nov 2021 16:02:13 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=suse.com; s=susede1; t=1635782533; h=from:from:reply-to:date:date:message-id:message-id:to:to:cc:cc: mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=aLrUd5dODKPXxykk4s6tizUbvYQTGhjxi6BtMoFjlTo=; b=Beevnq+qOaI1o8vAFTJnn8T7IFm7qLnloDGyiPfYe4vrCcoyPKxWo6ep01e49GK59NfvoX +bEHTUgedYzQjUYKPU1fpfRUATdJAEjtTZkGXPdTZ3uwV1FDC1eBMmw2L68O1azd6nWWp6 eoQVLuwjkf65E74QTWOktMKXogqLGT0= Received: from suse.cz (unknown [10.100.224.162]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by relay2.suse.de (Postfix) with ESMTPS id B79CCA3B94; Mon, 1 Nov 2021 16:02:12 +0000 (UTC) Date: Mon, 1 Nov 2021 17:02:12 +0100 From: Petr Mladek To: Yafang Shao Cc: Andrew Morton , Kees Cook , Steven Rostedt , Mathieu Desnoyers , Arnaldo Carvalho de Melo , Peter Zijlstra , Al Viro , Valentin Schneider , Qiang Zhang , robdclark , christian , Dietmar Eggemann , Ingo Molnar , Juri Lelli , Vincent Guittot , David Miller , Jakub Kicinski , Alexei Starovoitov , Daniel Borkmann , Andrii Nakryiko , Martin Lau , Song Liu , Yonghong Song , john fastabend , KP Singh , dennis.dalessandro@cornelisnetworks.com, mike.marciniszyn@cornelisnetworks.com, dledford@redhat.com, jgg@ziepe.ca, linux-rdma@vger.kernel.org, netdev , bpf , "linux-perf-use." , linux-fsdevel@vger.kernel.org, Linux MM , LKML , kernel test robot , kbuild test robot Subject: Re: [PATCH v7 00/11] extend task comm from 16 to 24 Message-ID: References: <20211101060419.4682-1-laoar.shao@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@vger.kernel.org On Mon 2021-11-01 22:34:30, Yafang Shao wrote: > On Mon, Nov 1, 2021 at 10:07 PM Petr Mladek wrote: > > On Mon 2021-11-01 06:04:08, Yafang Shao wrote: > > > 4. Print a warning if the kthread comm is still truncated. > > > > > > 5. What will happen to the out-of-tree tools after this change? > > > If the tool get task comm through kernel API, for example prctl(2), > > > bpf_get_current_comm() and etc, then it doesn't matter how large the > > > user buffer is, because it will always get a string with a nul > > > terminator. While if it gets the task comm through direct string copy, > > > the user tool must make sure the copied string has a nul terminator > > > itself. As TASK_COMM_LEN is not exposed to userspace, there's no > > > reason that it must require a fixed-size task comm. > > > > The amount of code that has to be updated is really high. I am pretty > > sure that there are more potential buffer overflows left. > > > > You did not commented on the concerns in the thread > > https://lore.kernel.org/all/CAADnVQKm0Ljj-w5PbkAu1ugLFnZRRPt-Vk-J7AhXxDD5xVompA@mail.gmail.com/ > > > I thought Steven[1] and Kees[2] have already clearly explained why we > do it like that, so I didn't give any more words on it. > > [1]. https://lore.kernel.org/all/20211025170503.59830a43@gandalf.local.home/ Steven was against switching task->comm[16] into a dynamically allocated pointer. But he was not against storing longer names separately. > [2]. https://lore.kernel.org/all/202110251406.56F87A3522@keescook/ Honestly, I am a bit confused by Kees' answer. IMHO, he agreed that switching task->comm[16] into a pointer was not worth it. But I am not sure what he meant by "Agreed -- this is a small change for what is already an "uncommon" corner case." > > Several people suggested to use a more conservative approach. > > Yes, they are Al[3] and Alexei[4]. > > [3]. https://lore.kernel.org/lkml/YVkmaSUxbg%2FJtBHb@zeniv-ca.linux.org.uk/ IMHO, Al suggested to store the long name separately and return it by proc_task_name() when available. > [4]. https://lore.kernel.org/all/CAADnVQKm0Ljj-w5PbkAu1ugLFnZRRPt-Vk-J7AhXxDD5xVompA@mail.gmail.com/ Alexei used dentry->d_iname as an exaxmple. struct dentry uses d_iname[DNAME_INLINE_LEN] for short names. And dynamically allocated d_name for long names, see *__d_alloc() implementation. > > I mean > > to keep comm[16] as is and add a new pointer to the full name. The buffer > > for the long name might be dynamically allocated only when needed. > > > > That would add a new allocation in the fork() for the threads with a long name. > I'm not sure if it is worth it. The allocation will be done only when needed. IMHO, the performance is important only for userspace processes. I am not aware of any kernel subsystem that would heavily create and destroy kthreads. > > The pointer might be either in task_struct or struct kthread. It might > > be used the same way as the full name stored by workqueue kthreads. > > > > If we decide to do it like that, I think we'd better add it in > task_struct, then it will work for all tasks. Is it really needed for userspace processes? For example, ps shows the information from /proc/*/cmdline instead. > > The advantage of the separate pointer: > > > > + would work for names longer than 32 > > + will not open security holes in code > > > > Yes, those are the advantages. And the disadvantage of it is: > > - new allocation in fork() It should not be a problem if we do it only when necessary and only for kthreads. Best Regards, Petr