From: Alexei Starovoitov <alexei.starovoitov@gmail.com>
To: sdf@google.com
Cc: davem@davemloft.net, daniel@iogearbox.net,
netdev@vger.kernel.org, bpf@vger.kernel.org, kernel-team@fb.com,
linux-security-module@vger.kernel.org, acme@redhat.com,
jamorris@linux.microsoft.com, jannh@google.com,
kpsingh@google.com
Subject: Re: [PATCH v5 bpf-next 2/3] bpf: implement CAP_BPF
Date: Mon, 11 May 2020 19:36:41 -0700 [thread overview]
Message-ID: <20200512023641.jupgmhpliblkli4t@ast-mbp.dhcp.thefacebook.com> (raw)
In-Reply-To: <20200512001210.GA235661@google.com>
On Mon, May 11, 2020 at 05:12:10PM -0700, sdf@google.com wrote:
> On 05/08, Alexei Starovoitov wrote:
> > From: Alexei Starovoitov <ast@kernel.org>
> [..]
> > @@ -3932,7 +3977,7 @@ SYSCALL_DEFINE3(bpf, int, cmd, union bpf_attr
> > __user *, uattr, unsigned int, siz
> > union bpf_attr attr;
> > int err;
>
> > - if (sysctl_unprivileged_bpf_disabled && !capable(CAP_SYS_ADMIN))
> > + if (sysctl_unprivileged_bpf_disabled && !bpf_capable())
> > return -EPERM;
> This is awesome, thanks for reviving the effort!
>
> One question I have about this particular snippet:
> Does it make sense to drop bpf_capable checks for the operations
> that work on a provided fd?
Above snippet is for the case when sysctl switches unpriv off.
It was a big hammer and stays big hammer.
I certainly would like to improve the situation, but I suspect
the folks who turn that sysctl knob on are simply paranoid about bpf
and no amount of reasoning would turn them around.
> The use-case I have in mind is as follows:
> * privileged (CAP_BPF) process loads the programs/maps and pins
> them at some known location
> * unprivileged process opens up those pins and does the following:
> * prepares the maps (and will later on read them)
> * does SO_ATTACH_BPF/SO_ATTACH_REUSEPORT_EBPF which afaik don't
> require any capabilities
>
> This essentially pushes some of the permission checks into a fs layer. So
> whoever has a file descriptor (via unix sock or open) can do BPF operations
> on the object that represents it.
cap_bpf doesn't change things in that regard.
Two cases here:
sysctl_unprivileged_bpf_disabled==0:
Unpriv can load socket_filter prog type and unpriv can attach it
via SO_ATTACH_BPF/SO_ATTACH_REUSEPORT_EBPF.
sysctl_unprivileged_bpf_disabled==1:
cap_sys_admin can load socket_filter and unpriv can attach it.
With addition of cap_bpf in the second case cap_bpf process can
load socket_filter too.
It doesn't mean that permissions are pushed into fs layer.
I'm not sure that relaxing of sysctl_unprivileged_bpf_disabled
will be well received.
Are you proposing to selectively allow certain bpf syscall commands
even when sysctl_unprivileged_bpf_disabled==1 ?
Like allow unpriv to do BPF_OBJ_GET to get an fd from bpffs ?
And allow unpriv to do map_update ?
It makes complete sense to me, but I'd like to argue about that
independently from this cap_bpf set.
We can relax that sysctl later.
next prev parent reply other threads:[~2020-05-12 2:36 UTC|newest]
Thread overview: 21+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-05-08 21:53 [PATCH v5 bpf-next 0/3] Introduce CAP_BPF Alexei Starovoitov
2020-05-08 21:53 ` [PATCH v5 bpf-next 1/3] bpf, capability: " Alexei Starovoitov
2020-05-08 21:53 ` [PATCH v5 bpf-next 2/3] bpf: implement CAP_BPF Alexei Starovoitov
2020-05-12 0:12 ` sdf
2020-05-12 2:36 ` Alexei Starovoitov [this message]
2020-05-12 12:50 ` Jordan Glover
2020-05-12 15:46 ` Alexei Starovoitov
2020-05-12 15:54 ` sdf
2020-05-12 18:39 ` Alexei Starovoitov
2020-05-12 14:35 ` Daniel Borkmann
2020-05-12 18:25 ` Alexei Starovoitov
2020-05-12 20:07 ` Daniel Borkmann
2020-05-12 22:56 ` Alexei Starovoitov
2020-05-12 15:05 ` Daniel Borkmann
2020-05-12 18:29 ` Alexei Starovoitov
2020-05-12 20:09 ` Daniel Borkmann
2020-05-12 20:27 ` Daniel Borkmann
2020-05-12 23:01 ` Alexei Starovoitov
2020-05-08 21:53 ` [PATCH v5 bpf-next 3/3] selftests/bpf: use CAP_BPF and CAP_PERFMON in tests Alexei Starovoitov
2020-05-08 22:45 ` [PATCH v5 bpf-next 0/3] Introduce CAP_BPF Casey Schaufler
2020-05-08 23:00 ` Alexei Starovoitov
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