netdev - Re: [RFC][PATCH kernel_bpf] honor CAP_NET_ADMIN for BPF_PROG

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Date:   Mon, 3 Jun 2019 19:12:26 +0200
From:   Nicolas Dichtel <nicolas.dichtel@...nd.com>
To:     Andreas Steinmetz <ast@...dv.de>, netdev@...r.kernel.org,
        bpf@...r.kernel.org
Subject: Re: [RFC][PATCH kernel_bpf] honor CAP_NET_ADMIN for BPF_PROG_LOAD

Le 28/05/2019 à 18:53, Andreas Steinmetz a écrit :
> [sorry for crossposting but this affects both lists]
> 
> BPF_PROG_TYPE_SCHED_CLS and BPF_PROG_TYPE_XDP should be allowed
> for CAP_NET_ADMIN capability. Nearly everything one can do with
> these program types can be done some other way with CAP_NET_ADMIN
> capability (e.g. NFQUEUE), but only slower.
> 
> This change is similar in behaviour to the /proc/sys/net
> CAP_NET_ADMIN exemption.
> 
> Overall chances are of increased security as network related
> applications do no longer require to keep CAP_SYS_ADMIN
> admin capability for network related eBPF operations.
> 
> It may well be that other program types than BPF_PROG_TYPE_XDP
> and BPF_PROG_TYPE_SCHED_CLS do need the same exemption, though
> I do not have sufficient knowledge of other program types
> to be able to decide this.
> 
> Preloading BPF programs is not possible in case of application
> modified or generated BPF programs, so this is no alternative.
> The verifier does prevent the BPF program from doing harmful
> things anyway.
> 
> Signed-off-by: Andreas Steinmetz <ast@...dv.de>
It makes sense to me.
Do you plan to submit it formally?

Looking a bit more at this topic, I see that most part of the bpf code uses
capable(CAP_NET_ADMIN). I don't see why we cannot use ns_capable(CAP_NET_ADMIN).


Regards,
Nicolas

> 
> --- a/kernel/bpf/syscall.c	2019-05-28 18:00:40.472841432 +0200
> +++ b/kernel/bpf/syscall.c	2019-05-28 18:17:50.162811510 +0200
> @@ -1561,8 +1561,13 @@ static int bpf_prog_load(union bpf_attr
>  		return -E2BIG;
>  	if (type != BPF_PROG_TYPE_SOCKET_FILTER &&
>  	    type != BPF_PROG_TYPE_CGROUP_SKB &&
> -	    !capable(CAP_SYS_ADMIN))
> -		return -EPERM;
> +	    !capable(CAP_SYS_ADMIN)) {
> +		if (type != BPF_PROG_TYPE_SCHED_CLS &&
> +		    type != BPF_PROG_TYPE_XDP)
> +			return -EPERM;
> +		if(!capable(CAP_NET_ADMIN))
> +			return -EPERM;
> +	}
>  
>  	bpf_prog_load_fixup_attach_type(attr);
>  	if (bpf_prog_load_check_attach_type(type, attr->expected_attach_type))
>