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 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 index 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 ` 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
Linux-Security-Module Archive on lore.kernel.org Archives are clonable: git clone --mirror https://lore.kernel.org/linux-security-module/0 linux-security-module/git/0.git # If you have public-inbox 1.1+ installed, you may # initialize and index your mirror using the following commands: public-inbox-init -V2 linux-security-module linux-security-module/ https://lore.kernel.org/linux-security-module \ linux-security-module@vger.kernel.org public-inbox-index linux-security-module Example config snippet for mirrors Newsgroup available over NNTP: nntp://nntp.lore.kernel.org/org.kernel.vger.linux-security-module AGPL code for this site: git clone https://public-inbox.org/public-inbox.git