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Reply-To: nicolas.dichtel@6wind.com
Subject: Re: [PATCH v2 4/4] bpf: export bpf_jit_current
To:     Lorenz Bauer <lmb@cloudflare.com>
Cc:     Luke Nelson <luke.r.nels@gmail.com>,
        Jonathan Corbet <corbet@lwn.net>,
        Alexei Starovoitov <ast@kernel.org>,
        Daniel Borkmann <daniel@iogearbox.net>,
        Andrii Nakryiko <andrii@kernel.org>,
        "David S. Miller" <davem@davemloft.net>,
        Jakub Kicinski <kuba@kernel.org>,
        kernel-team <kernel-team@cloudflare.com>,
        linux-doc@vger.kernel.org, LKML <linux-kernel@vger.kernel.org>,
        Networking <netdev@vger.kernel.org>, bpf <bpf@vger.kernel.org>
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From:   Nicolas Dichtel <nicolas.dichtel@6wind.com>
Organization: 6WIND
Message-ID: <1792748b-9204-c96e-b9c6-367eb19928cb@6wind.com>
Date:   Wed, 13 Oct 2021 14:29:17 +0200
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Le 13/10/2021 à 10:35, Lorenz Bauer a écrit :
> On Tue, 12 Oct 2021 at 17:29, Nicolas Dichtel <nicolas.dichtel@6wind.com> wrote:
>>
>> Le 12/10/2021 à 15:59, Lorenz Bauer a écrit :
>>> Expose bpf_jit_current as a read only value via sysctl.
>>>
>>> Signed-off-by: Lorenz Bauer <lmb@cloudflare.com>
>>> ---
>>
>> [snip]
>>
>>> +     {
>>> +             .procname       = "bpf_jit_current",
>>> +             .data           = &bpf_jit_current,
>>> +             .maxlen         = sizeof(long),
>>> +             .mode           = 0400,
>> Why not 0444 ?
> 
> This mirrors what the other BPF related sysctls do, which only allow
> access from root with CAP_SYS_ADMIN. I'd prefer 0444 as well, but
> Daniel explicitly locked down these sysctls in
> 2e4a30983b0f9b19b59e38bbf7427d7fdd480d98.
Even after this patch, bpf_jit_enable is 0644.

In fact, if you have CAP_BPF or CAP_SYS_ADMIN, this value has no impact for your
programs. But I you don't have one of these capabilities, it may be rejected,
but you cannot read these values, which help to understand why.


Regards,
Nicolas