netdev - Re: [PATCH v5 bpf-next 2/3] bpf: implement CAP

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Date:   Tue, 12 May 2020 12:50:05 +0000
From:   Jordan Glover <Golden_Miller83@...tonmail.ch>
To:     Alexei Starovoitov <alexei.starovoitov@...il.com>
Cc:     "sdf@...gle.com" <sdf@...gle.com>,
        "davem@...emloft.net" <davem@...emloft.net>,
        "daniel@...earbox.net" <daniel@...earbox.net>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "bpf@...r.kernel.org" <bpf@...r.kernel.org>,
        "kernel-team@...com" <kernel-team@...com>,
        "linux-security-module@...r.kernel.org" 
        <linux-security-module@...r.kernel.org>,
        "acme@...hat.com" <acme@...hat.com>,
        "jamorris@...ux.microsoft.com" <jamorris@...ux.microsoft.com>,
        "jannh@...gle.com" <jannh@...gle.com>,
        "kpsingh@...gle.com" <kpsingh@...gle.com>
Subject: Re: [PATCH v5 bpf-next 2/3] bpf: implement CAP_BPF

On Tuesday, May 12, 2020 2:36 AM, Alexei Starovoitov <alexei.starovoitov@...il.com> wrote:

> On Mon, May 11, 2020 at 05:12:10PM -0700, sdf@...gle.com wrote:
>
> > On 05/08, Alexei Starovoitov wrote:
> >
> > > From: Alexei Starovoitov ast@...nel.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.
>

Without CAP_BPF, sysctl was the only option to keep you safe from flow
of bpf vulns. You didn't had to be paranoid about that.

Jordan