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Mon, 25 Oct 2021 22:19:28 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0053.hostedemail.com [216.40.44.53]) by kanga.kvack.org (Postfix) with ESMTP id 626E0940007 for ; Mon, 25 Oct 2021 22:19:28 -0400 (EDT) Received: from smtpin16.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay01.hostedemail.com (Postfix) with ESMTP id 1D4CE1802FA25 for ; Tue, 26 Oct 2021 02:19:28 +0000 (UTC) X-FDA: 78736982016.16.463FC85 Received: from mail-io1-f51.google.com (mail-io1-f51.google.com [209.85.166.51]) by imf24.hostedemail.com (Postfix) with ESMTP id BF7ABB0000A7 for ; Tue, 26 Oct 2021 02:19:27 +0000 (UTC) Received: by mail-io1-f51.google.com with SMTP id i189so18251045ioa.1 for ; Mon, 25 Oct 2021 19:19:27 -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=k0RKbIIOqMFBOFiljOedZCbcAtZDA7g3jIfQe8Pm7Ic=; b=aoW6OTWlAGkoz5LLHjyuVeW61Uayophh62a+WB1/EWekYjdNjm+OIaF6sEZbcWwtwX occKhayjuggtGGnbc1xtLBNL5iw9jX+AIJgBpx9pJ/auW3IzdhtWxC9PkKi8+lo/GH4X fmGQ/4mcxJm6+UPYs4eeeYv1A24KKwMjyYuQm6r9b4M+K2F59SwhVyjt/0obUWXvgU9G QSYGUm2Jy8+JqhNZIYz14iZeOnC6WpXwOsOgQZPg5fBOia66yMZPK2tfUGrWI63BKu/8 zXFs+Oo6I+YPCihBQeMLpcZtxy0SDmKd74abqUCteI5tzt/DBWYOVurt9Pu8bsYf5WgH tcVw== 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=k0RKbIIOqMFBOFiljOedZCbcAtZDA7g3jIfQe8Pm7Ic=; b=grm6rJ4ddEh+Mx+oxPNyLdC3F6me0m3EfnzvNg7g1bmbtD/F5a+P6iqbBUEbLfZrvn rVLfdcjzia2I/nQRV90slww42Ld4Z3nEQcHFIL70kMr4jPwwPHXddxyAFEKNNkmpWKC0 71Mi6104fhoHy7yMP+pArk7vCEt9yczEDoXTIfQFnz92CBBJYR15jt6RY6qAk7wVfghi E+LpdpO5aPb7TTFHBN9MI65JniC4/d+VSNAd1MyUz5Ii4a/NWHURbmc33YuzgcZ4RSSv mi5RHjHpM6fk7NFRcxiq4h04M6UvCh4IY+OzN0sT7FxqpiGye+SsGoPCH1Nc1pWC7EDe FzmA== X-Gm-Message-State: AOAM531AxG4Z4c/lIVcpYkcvraUYbg61uyI5ETsoi6QewTjmEpWvGmR4 hqE7WrZ+r7a47AKVqz7VzxhB1ihZKoYqQF4zwkE= X-Google-Smtp-Source: ABdhPJwrAN4fbPYm/5hVv3F2xPLmeiEevoR0k3peWC93PQke/ju+UCPMkqMqGcfkxXu+OioRuTJdpiYFOpyzOJm9wqw= X-Received: by 2002:a05:6638:1607:: with SMTP id x7mr12892000jas.128.1635214767233; Mon, 25 Oct 2021 19:19:27 -0700 (PDT) MIME-Version: 1.0 References: <20211025083315.4752-1-laoar.shao@gmail.com> <20211025083315.4752-9-laoar.shao@gmail.com> <202110251421.7056ACF84@keescook> In-Reply-To: <202110251421.7056ACF84@keescook> From: Yafang Shao Date: Tue, 26 Oct 2021 10:18:51 +0800 Message-ID: Subject: Re: [PATCH v6 08/12] tools/bpf/bpftool/skeleton: make it adopt to task comm size change To: Kees Cook Cc: Andrew Morton , Steven Rostedt , 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" X-Rspamd-Server: rspam03 X-Rspamd-Queue-Id: BF7ABB0000A7 X-Stat-Signature: q3d384rcifh7nj486f9q5zircn5hksez Authentication-Results: imf24.hostedemail.com; dkim=pass header.d=gmail.com header.s=20210112 header.b=aoW6OTWl; dmarc=pass (policy=none) header.from=gmail.com; spf=pass (imf24.hostedemail.com: domain of laoar.shao@gmail.com designates 209.85.166.51 as permitted sender) smtp.mailfrom=laoar.shao@gmail.com X-HE-Tag: 1635214767-628892 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Tue, Oct 26, 2021 at 5:24 AM Kees Cook wrote: > > On Mon, Oct 25, 2021 at 08:33:11AM +0000, Yafang Shao wrote: > > bpf_probe_read_kernel_str() will add a nul terminator to the dst, then > > we don't care about if the dst size is big enough. > > > > Signed-off-by: Yafang Shao > > Cc: Mathieu Desnoyers > > Cc: Arnaldo Carvalho de Melo > > Cc: Andrii Nakryiko > > Cc: Peter Zijlstra > > Cc: Steven Rostedt > > Cc: Al Viro > > Cc: Kees Cook > > Cc: Petr Mladek > > 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); > > -Kees > > > --- > > tools/bpf/bpftool/skeleton/pid_iter.bpf.c | 4 ++-- > > 1 file changed, 2 insertions(+), 2 deletions(-) > > > > diff --git a/tools/bpf/bpftool/skeleton/pid_iter.bpf.c b/tools/bpf/bpftool/skeleton/pid_iter.bpf.c > > index d9b420972934..f70702fcb224 100644 > > --- a/tools/bpf/bpftool/skeleton/pid_iter.bpf.c > > +++ b/tools/bpf/bpftool/skeleton/pid_iter.bpf.c > > @@ -71,8 +71,8 @@ int iter(struct bpf_iter__task_file *ctx) > > > > e.pid = task->tgid; > > e.id = get_obj_id(file->private_data, obj_type); > > - bpf_probe_read_kernel(&e.comm, sizeof(e.comm), > > - task->group_leader->comm); > > + bpf_probe_read_kernel_str(&e.comm, sizeof(e.comm), > > + task->group_leader->comm); > > bpf_seq_write(ctx->meta->seq, &e, sizeof(e)); > > > > return 0; > > -- > > 2.17.1 > > > > -- > Kees Cook -- Thanks Yafang