netdev - Re: [PATCH v3 bpf-next 2/3] bpf: implement CAP

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Date:   Thu, 5 Sep 2019 16:08:44 +0000
From:   Song Liu <songliubraving@...com>
To:     Alexei Starovoitov <alexei.starovoitov@...il.com>
CC:     Alexei Starovoitov <ast@...nel.org>,
        "David S . Miller" <davem@...emloft.net>,
        Daniel Borkmann <daniel@...earbox.net>,
        Peter Zijlstra <peterz@...radead.org>,
        Andy Lutomirski <luto@...capital.net>,
        Networking <netdev@...r.kernel.org>, bpf <bpf@...r.kernel.org>,
        Kernel Team <Kernel-team@...com>,
        "linux-api@...r.kernel.org" <linux-api@...r.kernel.org>
Subject: Re: [PATCH v3 bpf-next 2/3] bpf: implement CAP_BPF



> On Sep 4, 2019, at 8:15 PM, Alexei Starovoitov <alexei.starovoitov@...il.com> wrote:
> 
> On Thu, Sep 05, 2019 at 02:51:51AM +0000, Song Liu wrote:
>> 
>> 
>>> On Sep 4, 2019, at 6:32 PM, Alexei Starovoitov <alexei.starovoitov@...il.com> wrote:
>>> 
>>> On Thu, Sep 05, 2019 at 12:34:36AM +0000, Song Liu wrote:
>>>> 
>>>> 
>>>>> On Sep 4, 2019, at 11:43 AM, Alexei Starovoitov <ast@...nel.org> wrote:
>>>>> 
>>>>> Implement permissions as stated in uapi/linux/capability.h
>>>>> 
>>>>> Signed-off-by: Alexei Starovoitov <ast@...nel.org>
>>>>> 
>>>> 
>>>> [...]
>>>> 
>>>>> @@ -1648,11 +1648,11 @@ static int bpf_prog_load(union bpf_attr *attr, union bpf_attr __user *uattr)
>>>>> 	is_gpl = license_is_gpl_compatible(license);
>>>>> 
>>>>> 	if (attr->insn_cnt == 0 ||
>>>>> -	    attr->insn_cnt > (capable(CAP_SYS_ADMIN) ? BPF_COMPLEXITY_LIMIT_INSNS : BPF_MAXINSNS))
>>>>> +	    attr->insn_cnt > (capable_bpf() ? BPF_COMPLEXITY_LIMIT_INSNS : BPF_MAXINSNS))
>>>>> 		return -E2BIG;
>>>>> 	if (type != BPF_PROG_TYPE_SOCKET_FILTER &&
>>>>> 	    type != BPF_PROG_TYPE_CGROUP_SKB &&
>>>>> -	    !capable(CAP_SYS_ADMIN))
>>>>> +	    !capable_bpf())
>>>>> 		return -EPERM;
>>>> 
>>>> Do we allow load BPF_PROG_TYPE_SOCKET_FILTER and BPF_PROG_TYPE_CGROUP_SKB
>>>> without CAP_BPF? If so, maybe highlight in the header?
>>> 
>>> of course. there is no change in behavior.
>>> 'highlight in the header'?
>>> you mean in commit log?
>>> I think it's a bit weird to describe things in commit that patch
>>> is _not_ changing vs things that patch does actually change.
>>> This type of comment would be great in a doc though.
>>> The doc will be coming separately in the follow up assuming
>>> the whole thing lands. I'll remember to note that bit.
>> 
>> I meant capability.h:
>> 
>> + * CAP_BPF allows the following BPF operations:
>> + * - Loading all types of BPF programs
>> 
>> But CAP_BPF is not required to load all types of programs. 
> 
> yes, but above statement is still correct, right?
> 
> And right below it says:
> * CAP_BPF allows the following BPF operations:
> * - Loading all types of BPF programs
> * - Creating all types of BPF maps except:
> *    - stackmap that needs CAP_TRACING
> *    - devmap that needs CAP_NET_ADMIN
> *    - cpumap that needs CAP_SYS_ADMIN
> which is also correct, but CAP_BPF is not required
> for array, hash, prog_array, percpu, map-in-map ...
> except their lru variants...
> and except if they contain bpf_spin_lock...
> and if they need BTF it currently can be loaded with cap_sys_admin only...
> 
> If we say something about socket_filter, cg_skb progs in capability.h
> we should clarify maps as well, but then it will become too big for .h
> The comments in capability.h already look too long to me.
> All that info and a lot more belongs in the doc.

Agreed. We cannot put all these details in capability.h. Doc/wikipages 
would be better fit for these information. 

Thanks,
Song