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Date:   Wed, 29 Apr 2020 15:44:16 +0100
From:   Quentin Monnet <quentin@...valent.com>
To:     Daniel Borkmann <daniel@...earbox.net>,
        Alexei Starovoitov <ast@...nel.org>
Cc:     bpf@...r.kernel.org, netdev@...r.kernel.org,
        Richard Palethorpe <rpalethorpe@...e.com>,
        Michael Kerrisk <mtk.manpages@...il.com>
Subject: Re: [PATCH bpf-next v2 2/3] tools: bpftool: allow unprivileged users
 to probe features

2020-04-29 16:35 UTC+0200 ~ Daniel Borkmann <daniel@...earbox.net>
> On 4/29/20 3:05 PM, Quentin Monnet wrote:
>> There is demand for a way to identify what BPF helper functions are
>> available to unprivileged users. To do so, allow unprivileged users to
>> run "bpftool feature probe" to list BPF-related features. This will only
>> show features accessible to those users, and may not reflect the full
>> list of features available (to administrators) on the system.
>>
>> To avoid the case where bpftool is inadvertently run as non-root and
>> would list only a subset of the features supported by the system when it
>> would be expected to list all of them, running as unprivileged is gated
>> behind the "unprivileged" keyword passed to the command line. When used
>> by a privileged user, this keyword allows to drop the CAP_SYS_ADMIN and
>> to list the features available to unprivileged users. Note that this
>> addsd a dependency on libpcap for compiling bpftool.
>>
>> Note that there is no particular reason why the probes were restricted
>> to root, other than the fact I did not need them for unprivileged and
>> did not bother with the additional checks at the time probes were added.
>>
>> Signed-off-by: Quentin Monnet <quentin@...valent.com>
>> ---
>>   .../bpftool/Documentation/bpftool-feature.rst |  10 +-
>>   tools/bpf/bpftool/Makefile                    |   2 +-
>>   tools/bpf/bpftool/bash-completion/bpftool     |   2 +-
>>   tools/bpf/bpftool/feature.c                   | 100 +++++++++++++++---
>>   4 files changed, 99 insertions(+), 15 deletions(-)
>>
>> diff --git a/tools/bpf/bpftool/Documentation/bpftool-feature.rst
>> b/tools/bpf/bpftool/Documentation/bpftool-feature.rst
>> index b04156cfd7a3..ca085944e4cf 100644
>> --- a/tools/bpf/bpftool/Documentation/bpftool-feature.rst
>> +++ b/tools/bpf/bpftool/Documentation/bpftool-feature.rst
>> @@ -19,7 +19,7 @@ SYNOPSIS
>>   FEATURE COMMANDS
>>   ================
>>   -|    **bpftool** **feature probe** [*COMPONENT*] [**full**]
>> [**macros** [**prefix** *PREFIX*]]
>> +|    **bpftool** **feature probe** [*COMPONENT*] [**full**]
>> [**unprivileged**] [**macros** [**prefix** *PREFIX*]]
>>   |    **bpftool** **feature help**
> 
> Looks good to me, thanks! There is one small thing missing which is
> updating
> do_help() to display the same as above from bpftool help, but rest lgtm.

Eh, I'm usually the one pointing that -_-. Thank you Daniel, v3 incoming.

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