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 48D74C433EF for ; Tue, 2 Nov 2021 01:10:31 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 2F08A60F70 for ; Tue, 2 Nov 2021 01:10:31 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231181AbhKBBNC (ORCPT ); Mon, 1 Nov 2021 21:13:02 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:60240 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229510AbhKBBNB (ORCPT ); Mon, 1 Nov 2021 21:13:01 -0400 Received: from mail-io1-xd31.google.com (mail-io1-xd31.google.com [IPv6:2607:f8b0:4864:20::d31]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 61536C061714; Mon, 1 Nov 2021 18:10:27 -0700 (PDT) Received: by mail-io1-xd31.google.com with SMTP id p204so12068454iod.8; Mon, 01 Nov 2021 18:10:27 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20210112; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=ehy0XSpOplhnJPTu2SM6YtwbIMUDDIgGBva5/Leuo6g=; b=kU0RbIUOhKfJFJr9pzzRahTBNVtJThLIwuxVQgVa0UWrRNIWFEIBPTbbB0qEGYvWNp AzPvhAt5Tfi+puIhqx1nzzkM5tZ3jcUhbuJykwycQI1Z101JFODOqr01uikeVGsur9Fv m5x+HGqyXbM+HSWP4l5Ez0Ah7tKirpVoDeP6hGQokvUBk/FwpHjWlXmYtS5nXhfsctbX tlk5ZGpMvMYsLihuUP+0uIkioIY0+DZ+fWHw+o7RmJI0PFqHXhX5ftuuk5m2BIw/66sE CET8s0UVR4DhKoNQ1plCJ+gNkvnVjCgz5DlSPhzTpxhn7g/Z288uSkopZgNS7p+4fAz/ la+Q== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=ehy0XSpOplhnJPTu2SM6YtwbIMUDDIgGBva5/Leuo6g=; b=6ajLUcrU8/astpNoESXYpY5k2KV4vdDhn/XSBOmU4uFi6IH9EMeXVNhN0KXtGyWtdu +mbXIZgH1JCavKUqBQ7BbnP1y6zhn1+G7Tc0ty3KCcXQGGwgBY/YItJ4zfIz8MD7usaL +FUkvtvgDfvtMdkqL0/egjsg4fOrx3IcPrswv8NaN0KokPQ9He6Rtesgzxr+6FUw3HIV 7AgkJRz6+JL4735Yp428zfyQUJ2ZGuM3eU54j1+yStEBXDKcvypRQ7LovS7N5mVPMmzi Hd0VsPnrygBzRUlyT/elWUvboqSfnPNTBaCZKn2nYXue7VZIczTA+66Ecfolo65G8Zdx z68g== X-Gm-Message-State: AOAM533T6YHXY/lTpqCnYNp/B3In69Jt9ytEztwlz0kvg6CG7dNutKQK UiWruCiAdghCMQLZuszVsWtRx6og5/sLpQlw1ABphtn0nHBiEB7B0oU= X-Google-Smtp-Source: ABdhPJzVw2x+5/HYLiwL7Md8DRLXERlLY4V+97Im04VA/lFA6YxKC1gsvipPZCBNZ/9b+5iz33+Fe76oRlCSo6q8zpc= X-Received: by 2002:a05:6638:386:: with SMTP id y6mr3807157jap.49.1635815426525; Mon, 01 Nov 2021 18:10:26 -0700 (PDT) MIME-Version: 1.0 References: <20211101060419.4682-1-laoar.shao@gmail.com> In-Reply-To: From: Yafang Shao Date: Tue, 2 Nov 2021 09:09:50 +0800 Message-ID: Subject: Re: [PATCH v7 00/11] extend task comm from 16 to 24 To: Petr Mladek 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 Content-Type: text/plain; charset="UTF-8" Precedence: bulk List-ID: X-Mailing-List: linux-rdma@vger.kernel.org On Tue, Nov 2, 2021 at 12:02 AM Petr Mladek wrote: > > 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. > Thanks for the summary. So with Stenven's new reply[1], the opinion in common is storing long names into a separate place. And no one is against it now. [1]. https://lore.kernel.org/lkml/20211101120636.3cfc5afa@gandalf.local.home/ > > > 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. > XFS may create many kthreads with longer names, especially if there're many partitions in the disk. For example, xfs-reclaim/sd{a, b, c, ...} xfs-blockgc/sd{a, b, c, ...} xfs-inodegc/sd{a, b, c, ...} They are supposed to be created at boot time, and shouldn't be heavily created and destroyed. > > > > 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. > Right. The userspace processes can be obtained from /proc/*/cmdline. > > > > 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. > So if no one against, I will do it in two steps, 1. Send the task comm cleanups in a separate patchset named "task comm cleanups" This patchset includes patch #1, #2, #4, #5, #6, #7 and #9. Cleaning them up can make it less error prone, and it will be helpful if we want to extend task comm in the future :) 2. Keep the current comm[16] as-is and introduce a separate pointer to store kthread's long name Now we only care about kthread, so we can put the pointer into a kthread specific struct. For example in the struct kthread, or in kthread->data (which may conflict with workqueue). And then dynamically allocate a longer name if it is truncated, for example, __kthread_create_on_node len = vsnprintf(name, sizeof(name), namefmt, args); if (len >= TASK_COMM_LEN) { /* create a longer name */ } And then we modify proc_task_name(), so the user can get kthread's longer name via /proc/[pid]/comm. And then free the allocated memory when the kthread is destroyed. -- Thanks Yafang