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[23.128.96.18]) by mx.google.com with ESMTP id l22si9497068ejo.536.2021.10.26.10.24.04; Tue, 26 Oct 2021 10:24:39 -0700 (PDT) Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18; Authentication-Results: mx.google.com; dkim=pass header.i=@gmail.com header.s=20210112 header.b=i7RAxoJj; spf=pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) smtp.mailfrom=linux-kernel-owner@vger.kernel.org; dmarc=pass (p=NONE sp=QUARANTINE dis=NONE) header.from=gmail.com Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S236338AbhJZN7D (ORCPT + 99 others); Tue, 26 Oct 2021 09:59:03 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:47562 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S236305AbhJZN6z (ORCPT ); Tue, 26 Oct 2021 09:58:55 -0400 Received: from mail-io1-xd2c.google.com (mail-io1-xd2c.google.com [IPv6:2607:f8b0:4864:20::d2c]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 55263C061767; Tue, 26 Oct 2021 06:56:31 -0700 (PDT) Received: by mail-io1-xd2c.google.com with SMTP id 188so20463374iou.12; Tue, 26 Oct 2021 06:56:31 -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=OCNly9Pv6GVtqK5WKlYGGpWZ1IwDTUSNcWIUnGMQ4tQ=; b=i7RAxoJj6vRHJO/QOSjI/2wZP40Tm49lxjwUghVRA9loicQXFZNhM0MArl94d+vLjQ 3ONCBgOGm6/Tzkk6/rbzph3fyWGtvF06KCpw5TQuJV+IYTHQLBvZq/yAsOXYH5zO2znh 0zjKS2Yzo3vcuKLciR7vPdHTMj2n1hFo604EAkwzdVdDIC4TDCtH88vI9tlkTdFe6ovD fUtyJV7cBcB5modNsKwvWcaeO4hCblmIqUYnQtEfhNC7w/zLGp7dGfWhIz6QBgu1TWLw 8Ux1Iqr2m7VjjSxbnvmsTLhMEWmkZE4cIbSrm9U8IZMkRyp3VWpS9uj1z99yX47jDUJn YTpg== 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=OCNly9Pv6GVtqK5WKlYGGpWZ1IwDTUSNcWIUnGMQ4tQ=; b=8FWOAAlleloW0xhPMxL+6GS5BexHx48d5GFmrTfGRKL214YQ4qDtQcHro6mpZHRT/f I/SychaEi7/a5YqNF2c3brqa5DsCp5V3ufu6zxcbPsMGFPk6fFukNH0vgLEf5HA+g6zn B3O1AtvPLmVFMzTybzBBt+jFq/2Y/MLH/gkoSFAMJ/uFx8Wbk3Ahy7sI4KwcZP3FP1Rb GNLExtKQUXIGtPUSBxl6oiQttRV1xWqLNnMbDBo60TwO7nRGDPh9/q1WOQ2TTv1f91HY o7eUwun0cj129c0D1qmMKl7J2fBAyxSXjh7yyKxtwCaWwX4TJrg4Ijo1CJXGWe5pcl2L nRyA== X-Gm-Message-State: AOAM532aw9v9bPEw3Mmnx6gT5nYW8jfDHqwZk4ykigptZjjYWbeDRJGZ lIMQoS0R4Md0VIfAgzsNjaN8U6nKj1tjHSuPjDg= X-Received: by 2002:a02:a483:: with SMTP id d3mr6171868jam.23.1635256590773; Tue, 26 Oct 2021 06:56:30 -0700 (PDT) MIME-Version: 1.0 References: <20211025083315.4752-1-laoar.shao@gmail.com> <20211025083315.4752-9-laoar.shao@gmail.com> <202110251421.7056ACF84@keescook> <20211026091211.569a7ba2@gandalf.local.home> In-Reply-To: <20211026091211.569a7ba2@gandalf.local.home> From: Yafang Shao Date: Tue, 26 Oct 2021 21:55:54 +0800 Message-ID: Subject: Re: [PATCH v6 08/12] tools/bpf/bpftool/skeleton: make it adopt to task comm size change To: Steven Rostedt Cc: Kees Cook , Andrew Morton , Mathieu Desnoyers , Arnaldo Carvalho de Melo , Petr Mladek , 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 , Andrii Nakryiko Content-Type: text/plain; charset="UTF-8" Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Oct 26, 2021 at 9:12 PM Steven Rostedt wrote: > > On Tue, 26 Oct 2021 10:18:51 +0800 > Yafang Shao wrote: > > > > So, if we're ever going to copying these buffers out of the kernel (I > > > don't know what the object lifetime here in bpf is for "e", etc), we > > > should be zero-padding (as get_task_comm() does). > > > > > > Should this, instead, be using a bounce buffer? > > > > The comment in bpf_probe_read_kernel_str_common() says > > > > : /* > > : * The strncpy_from_kernel_nofault() call will likely not fill the > > : * entire buffer, but that's okay in this circumstance as we're probing > > : * arbitrary memory anyway similar to bpf_probe_read_*() and might > > : * as well probe the stack. Thus, memory is explicitly cleared > > : * only in error case, so that improper users ignoring return > > : * code altogether don't copy garbage; otherwise length of string > > : * is returned that can be used for bpf_perf_event_output() et al. > > : */ > > > > It seems that it doesn't matter if the buffer is filled as that is > > probing arbitrary memory. > > > > > > > > get_task_comm(comm, task->group_leader); > > > > This helper can't be used by the BPF programs, as it is not exported to BPF. > > > > > bpf_probe_read_kernel_str(&e.comm, sizeof(e.comm), comm); > > I guess Kees is worried that e.comm will have something exported to user > space that it shouldn't. But since e is part of the BPF program, does the > BPF JIT take care to make sure everything on its stack is zero'd out, such > that a user BPF couldn't just read various items off its stack and by doing > so, see kernel memory it shouldn't be seeing? > Understood. It can leak information to the user if the user buffer is large enough. > I'm guessing it does, otherwise this would be a bigger issue than this > patch series. > I will think about how to fix it. At first glance, it seems we'd better introduce a new BPF helper like bpf_probe_read_kernel_str_pad(). -- Thanks Yafang