From: Andy Lutomirski <luto@kernel.org>
To: Song Liu <songliubraving@fb.com>
Cc: Andy Lutomirski <luto@kernel.org>,
Kees Cook <keescook@chromium.org>,
Networking <netdev@vger.kernel.org>, bpf <bpf@vger.kernel.org>,
Alexei Starovoitov <ast@kernel.org>,
Daniel Borkmann <daniel@iogearbox.net>,
Kernel Team <Kernel-team@fb.com>,
Lorenz Bauer <lmb@cloudflare.com>, Jann Horn <jannh@google.com>,
Greg KH <gregkh@linuxfoundation.org>,
Linux API <linux-api@vger.kernel.org>,
LSM List <linux-security-module@vger.kernel.org>
Subject: Re: [PATCH v2 bpf-next 1/4] bpf: unprivileged BPF access via /dev/bpf
Date: Sun, 4 Aug 2019 15:16:46 -0700 [thread overview]
Message-ID: <CALCETrU7NbBnXXsw1B+DvTkfTVRBFWXuJ8cZERCCNvdFG6KqRw@mail.gmail.com> (raw)
In-Reply-To: <5A2FCD7E-7F54-41E5-BFAE-BB9494E74F2D@fb.com>
On Fri, Aug 2, 2019 at 12:22 AM Song Liu <songliubraving@fb.com> wrote:
>
> Hi Andy,
>
>> I actually agree CAP_BPF_ADMIN makes sense. The hard part is to make
> >> existing tools (setcap, getcap, etc.) and libraries aware of the new CAP.
> >
> > It's been done before -- it's not that hard. IMO the main tricky bit
> > would be try be somewhat careful about defining exactly what
> > CAP_BPF_ADMIN does.
>
> Agreed. I think defining CAP_BPF_ADMIN could be a good topic for the
> Plumbers conference.
>
> OTOH, I don't think we have to wait for CAP_BPF_ADMIN to allow daemons
> like systemd to do sys_bpf() without root.
I don't understand the use case here. Are you talking about systemd
--user? As far as I know, a user is expected to be able to fully
control their systemd --user process, so giving it unrestricted bpf
access is very close to giving it superuser access, and this doesn't
sound like a good idea. I think that, if systemd --user needs bpf(),
it either needs real unprivileged bpf() or it needs a privileged
helper (SUID or a daemon) to intermediate this access.
>
> >
> >>> I don't see why you need to invent a whole new mechanism for this.
> >>> The entire cgroup ecosystem outside bpf() does just fine using the
> >>> write permission on files in cgroupfs to control access. Why can't
> >>> bpf() do the same thing?
> >>
> >> It is easier to use write permission for BPF_PROG_ATTACH. But it is
> >> not easy to do the same for other bpf commands: BPF_PROG_LOAD and
> >> BPF_MAP_*. A lot of these commands don't have target concept. Maybe
> >> we should have target concept for all these commands. But that is a
> >> much bigger project. OTOH, "all or nothing" model allows all these
> >> commands at once.
> >
> > For BPF_PROG_LOAD, I admit I've never understood why permission is
> > required at all. I think that CAP_SYS_ADMIN or similar should be
> > needed to get is_priv in the verifier, but I think that should mainly
> > be useful for tracing, and that requires lots of privilege anyway.
> > BPF_MAP_* is probably the trickiest part. One solution would be some
> > kind of bpffs, but I'm sure other solutions are possible.
>
> Improving permission management of cgroup_bpf is another good topic to
> discuss. However, it is also an overkill for current use case.
>
I looked at the code some more, and I don't think this is so hard
after all. As I understand it, all of the map..by_id stuff is, to
some extent, deprecated in favor of persistent maps. As I see it, the
map..by_id calls should require privilege forever, although I can
imagine ways to scope that privilege to a namespace if the maps
themselves were to be scoped to a namespace.
Instead, unprivileged tools would use the persistent map interface
roughly like this:
$ bpftool map create /sys/fs/bpf/my_dir/filename type hash key 8 value
8 entries 64 name mapname
This would require that the caller have either CAP_DAC_OVERRIDE or
that the caller have permission to create files in /sys/fs/bpf/my_dir
(using the same rules as for any filesystem), and the resulting map
would end up owned by the creating user and have mode 0600 (or maybe
0666, or maybe a new bpf_attr parameter) modified by umask. Then all
the various capable() checks that are currently involved in accessing
a persistent map would instead check FMODE_READ or FMODE_WRITE on the
map file as appropriate.
Half of this stuff already works. I just set my system up like this:
$ ls -l /sys/fs/bpf
total 0
drwxr-xr-x. 3 luto luto 0 Aug 4 15:10 luto
$ mkdir /sys/fs/bpf/luto/test
$ ls -l /sys/fs/bpf/luto
total 0
drwxrwxr-x. 2 luto luto 0 Aug 4 15:10 test
I bet that making the bpf() syscalls work appropriately in this
context without privilege would only be a couple of hours of work.
The hard work, creating bpffs and making it function, is already done
:)
P.S. The docs for bpftool create are less than fantastic. The
complete lack of any error message at all when the syscall returns
-EACCES is also not fantastic.
next prev parent reply other threads:[~2019-08-04 22:17 UTC|newest]
Thread overview: 61+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <20190627201923.2589391-1-songliubraving@fb.com>
[not found] ` <20190627201923.2589391-2-songliubraving@fb.com>
[not found] ` <21894f45-70d8-dfca-8c02-044f776c5e05@kernel.org>
[not found] ` <3C595328-3ABE-4421-9772-8D41094A4F57@fb.com>
[not found] ` <CALCETrWBnH4Q43POU8cQ7YMjb9LioK28FDEQf7aHZbdf1eBZWg@mail.gmail.com>
[not found] ` <0DE7F23E-9CD2-4F03-82B5-835506B59056@fb.com>
[not found] ` <CALCETrWBWbNFJvsTCeUchu3BZJ3SH3dvtXLUB2EhnPrzFfsLNA@mail.gmail.com>
[not found] ` <201907021115.DCD56BBABB@keescook>
[not found] ` <CALCETrXTta26CTtEDnzvtd03-WOGdXcnsAogP8JjLkcj4-mHvg@mail.gmail.com>
[not found] ` <4A7A225A-6C23-4C0F-9A95-7C6C56B281ED@fb.com>
[not found] ` <CALCETrX2bMnwC6_t4b_G-hzJSfMPrkK4YKs5ebcecv2LJ0rt3w@mail.gmail.com>
[not found] ` <514D5453-0AEE-420F-AEB6-3F4F58C62E7E@fb.com>
[not found] ` <1DE886F3-3982-45DE-B545-67AD6A4871AB@amacapital.net>
[not found] ` <7F51F8B8-CF4C-4D82-AAE1-F0F28951DB7F@fb.com>
[not found] ` <77354A95-4107-41A7-8936-D144F01C3CA4@fb.com>
[not found] ` <369476A8-4CE1-43DA-9239-06437C0384C7@fb.com>
2019-07-30 20:24 ` [PATCH v2 bpf-next 1/4] bpf: unprivileged BPF access via /dev/bpf Andy Lutomirski
2019-07-31 8:10 ` Song Liu
2019-07-31 19:09 ` Andy Lutomirski
2019-08-02 7:21 ` Song Liu
2019-08-04 22:16 ` Andy Lutomirski [this message]
2019-08-05 0:08 ` Andy Lutomirski
2019-08-05 5:47 ` Andy Lutomirski
2019-08-05 7:36 ` Song Liu
2019-08-05 17:23 ` Andy Lutomirski
2019-08-05 19:21 ` Alexei Starovoitov
2019-08-05 21:25 ` Andy Lutomirski
2019-08-05 22:21 ` Andy Lutomirski
2019-08-06 1:11 ` Alexei Starovoitov
2019-08-07 5:24 ` Andy Lutomirski
2019-08-07 9:03 ` Lorenz Bauer
2019-08-07 13:52 ` Andy Lutomirski
2019-08-13 21:58 ` Alexei Starovoitov
2019-08-13 22:26 ` Daniel Colascione
2019-08-13 23:24 ` Andy Lutomirski
2019-08-13 23:06 ` Andy Lutomirski
2019-08-14 0:57 ` Alexei Starovoitov
2019-08-14 17:51 ` Andy Lutomirski
2019-08-14 22:05 ` Alexei Starovoitov
2019-08-14 22:30 ` Andy Lutomirski
2019-08-14 23:33 ` Alexei Starovoitov
2019-08-14 23:59 ` Andy Lutomirski
2019-08-15 0:36 ` Alexei Starovoitov
2019-08-15 11:24 ` Jordan Glover
2019-08-15 17:28 ` Alexei Starovoitov
2019-08-15 18:36 ` Andy Lutomirski
2019-08-15 23:08 ` Alexei Starovoitov
2019-08-16 9:34 ` Jordan Glover
2019-08-16 9:59 ` Thomas Gleixner
2019-08-16 11:33 ` Jordan Glover
2019-08-16 19:52 ` Alexei Starovoitov
2019-08-16 20:28 ` Thomas Gleixner
2019-08-17 15:02 ` Alexei Starovoitov
2019-08-17 15:44 ` Andy Lutomirski
2019-08-19 9:15 ` Thomas Gleixner
2019-08-19 17:27 ` Alexei Starovoitov
2019-08-19 17:38 ` Andy Lutomirski
2019-08-15 18:43 ` Jordan Glover
2019-08-15 19:46 ` Kees Cook
2019-08-15 23:46 ` Alexei Starovoitov
2019-08-16 0:54 ` Andy Lutomirski
2019-08-16 5:56 ` Song Liu
2019-08-16 21:45 ` Alexei Starovoitov
2019-08-16 22:22 ` Christian Brauner
2019-08-17 15:08 ` Alexei Starovoitov
2019-08-17 15:16 ` Christian Brauner
2019-08-17 15:36 ` Alexei Starovoitov
2019-08-17 15:42 ` Christian Brauner
2019-08-22 14:17 ` Daniel Borkmann
2019-08-22 15:16 ` Andy Lutomirski
2019-08-22 15:17 ` RFC: very rough draft of a bpf permission model Andy Lutomirski
2019-08-22 23:26 ` Alexei Starovoitov
2019-08-23 23:09 ` Andy Lutomirski
2019-08-26 22:36 ` Alexei Starovoitov
2019-08-27 0:05 ` Andy Lutomirski
2019-08-27 0:34 ` Alexei Starovoitov
2019-08-22 22:48 ` [PATCH v2 bpf-next 1/4] bpf: unprivileged BPF access via /dev/bpf Alexei Starovoitov
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=CALCETrU7NbBnXXsw1B+DvTkfTVRBFWXuJ8cZERCCNvdFG6KqRw@mail.gmail.com \
--to=luto@kernel.org \
--cc=Kernel-team@fb.com \
--cc=ast@kernel.org \
--cc=bpf@vger.kernel.org \
--cc=daniel@iogearbox.net \
--cc=gregkh@linuxfoundation.org \
--cc=jannh@google.com \
--cc=keescook@chromium.org \
--cc=linux-api@vger.kernel.org \
--cc=linux-security-module@vger.kernel.org \
--cc=lmb@cloudflare.com \
--cc=netdev@vger.kernel.org \
--cc=songliubraving@fb.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).