From: "Toke Høiland-Jørgensen" <email@example.com>
To: Andrii Nakryiko <firstname.lastname@example.org>
Cc: Andrii Nakryiko <email@example.com>, bpf <firstname.lastname@example.org>,
Alexei Starovoitov <email@example.com>,
Daniel Borkmann <firstname.lastname@example.org>,
Kernel Team <email@example.com>
Subject: Re: [RFC PATCH bpf-next 4/8] bpf: support GET_FD_BY_ID and GET_NEXT_ID for bpf_link
Date: Tue, 14 Apr 2020 12:32:04 +0200 [thread overview]
Message-ID: <firstname.lastname@example.org> (raw)
Andrii Nakryiko <email@example.com> writes:
>> > After that, one can pin bpf_link temporarily and re-open it as
>> > writable one, provided CAP_DAC_OVERRIDE capability is present. All
>> > that works already, because pinned bpf_link is just a file, so one can
>> > do fchmod on it and all that will go through normal file access
>> > permission check code path.
>> Ah, I did not know that was possible - I was assuming that bpffs was
>> doing something special to prevent that. But if not, great!
>> > Unfortunately, just re-opening same FD as writable (which would
>> > be possible if fcntl(fd, F_SETFL, S_IRUSR
>> > S_IWUSR) was supported on Linux) without pinning is not possible.
>> > Opening link from /proc/<pid>/fd/<link-fd> doesn't seem to work
>> > either, because backing inode is not BPF FS inode. I'm not sure, but
>> > maybe we can support the latter eventually. But either way, I think
>> > given this is to be used for manual troubleshooting, going through few
>> > extra hoops to force-detach bpf_link is actually a good thing.
>> Hmm, I disagree that deliberately making users jump through hoops is a
>> good thing. Smells an awful lot like security through obscurity to me;
>> and we all know how well that works anyway...
> Depends on who users are? bpftool can implement this as one of
> `bpftool link` sub-commands and allow human operators to force-detach
> bpf_link, if necessary.
Yeah, I would expect this to be the common way this would be used: built
> I think applications shouldn't do this (programmatically) at all,
> which is why I think it's actually good that it's harder and not
> obvious, this will make developer think again before implementing
> this, hopefully. For me it's about discouraging bad practice.
I guess I just don't share your optimism that making people jump through
hoops will actually discourage them :)
If people know what they are doing it should be enough to document it as
discouraged. And if they don't, they are perfectly capable of finding
and copy-pasting the sequence of hoop-jumps required to achieve what
they want, probably with more bugs added along the way.
So in the end I think that all you're really achieving is annoying
people who do have a legitimate reason to override the behaviour (which
includes yourself as a bpftool developer :)). That's what I meant by the
'security through obscurity' comment.
next prev parent reply other threads:[~2020-04-14 10:32 UTC|newest]
Thread overview: 24+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-04-04 0:09 [RFC PATCH bpf-next 0/8] bpf_link observability APIs Andrii Nakryiko
2020-04-04 0:09 ` [RFC PATCH bpf-next 1/8] bpf: refactor bpf_link update handling Andrii Nakryiko
2020-04-04 0:09 ` [RFC PATCH bpf-next 2/8] bpf: allow bpf_link pinning as read-only and enforce LINK_UPDATE Andrii Nakryiko
2020-04-04 0:09 ` [RFC PATCH bpf-next 3/8] bpf: allocate ID for bpf_link Andrii Nakryiko
2020-04-04 0:09 ` [RFC PATCH bpf-next 4/8] bpf: support GET_FD_BY_ID and GET_NEXT_ID " Andrii Nakryiko
2020-04-06 11:34 ` Toke Høiland-Jørgensen
2020-04-06 19:06 ` Andrii Nakryiko
2020-04-08 15:14 ` Toke Høiland-Jørgensen
2020-04-08 20:23 ` Andrii Nakryiko
2020-04-08 21:21 ` Toke Høiland-Jørgensen
2020-04-09 18:49 ` Andrii Nakryiko
2020-04-14 10:32 ` Toke Høiland-Jørgensen [this message]
2020-04-14 18:47 ` Andrii Nakryiko
2020-04-15 9:26 ` Toke Høiland-Jørgensen
2020-04-04 0:09 ` [RFC PATCH bpf-next 5/8] bpf: add support for BPF_OBJ_GET_INFO_BY_FD " Andrii Nakryiko
2020-04-06 11:34 ` Toke Høiland-Jørgensen
2020-04-06 18:58 ` Andrii Nakryiko
2020-04-04 0:09 ` [RFC PATCH bpf-next 6/8] libbpf: add low-level APIs for new bpf_link commands Andrii Nakryiko
2020-04-04 0:09 ` [RFC PATCH bpf-next 7/8] bpftool: expose attach_type-to-string array to non-cgroup code Andrii Nakryiko
2020-04-04 0:09 ` [RFC PATCH bpf-next 8/8] bpftool: add bpf_link show and pin support Andrii Nakryiko
2020-04-08 23:44 ` David Ahern
2020-04-09 18:50 ` Andrii Nakryiko
2020-04-05 16:26 ` [RFC PATCH bpf-next 0/8] bpf_link observability APIs David Ahern
2020-04-05 18:31 ` Andrii Nakryiko
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