netdev - Re: [PATCH v2 bpf-next 2/3] bpf: implement CAP

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Date:   Thu, 29 Aug 2019 10:30:35 -0700
From:   Alexei Starovoitov <alexei.starovoitov@...il.com>
To:     Daniel Borkmann <daniel@...earbox.net>
Cc:     Alexei Starovoitov <ast@...nel.org>, luto@...capital.net,
        davem@...emloft.net, peterz@...radead.org, rostedt@...dmis.org,
        netdev@...r.kernel.org, bpf@...r.kernel.org, kernel-team@...com,
        linux-api@...r.kernel.org
Subject: Re: [PATCH v2 bpf-next 2/3] bpf: implement CAP_BPF

On Thu, Aug 29, 2019 at 05:32:27PM +0200, Daniel Borkmann wrote:
> On 8/29/19 7:12 AM, Alexei Starovoitov wrote:
> > Implement permissions as stated in uapi/linux/capability.h
> > 
> > Note that CAP_SYS_ADMIN is replaced with CAP_BPF.
> > All existing applications that use BPF do not drop all caps
> > and keep only CAP_SYS_ADMIN before doing bpf() syscall.
> > Hence it's highly unlikely that existing code will break.
> > If there will be reports of breakage then CAP_SYS_ADMIN
> > would be allowed as well with "it's usage is deprecated" message
> > similar to commit ee24aebffb75 ("cap_syslog: accept CAP_SYS_ADMIN for now")
> > 
> > Signed-off-by: Alexei Starovoitov <ast@...nel.org>
> [...]
> > diff --git a/kernel/bpf/hashtab.c b/kernel/bpf/hashtab.c
> > index 22066a62c8c9..f459315625ac 100644
> > --- a/kernel/bpf/hashtab.c
> > +++ b/kernel/bpf/hashtab.c
> > @@ -244,9 +244,9 @@ static int htab_map_alloc_check(union bpf_attr *attr)
> >   	BUILD_BUG_ON(offsetof(struct htab_elem, fnode.next) !=
> >   		     offsetof(struct htab_elem, hash_node.pprev));
> > -	if (lru && !capable(CAP_SYS_ADMIN))
> > +	if (lru && !capable(CAP_BPF))
> >   		/* LRU implementation is much complicated than other
> > -		 * maps.  Hence, limit to CAP_SYS_ADMIN for now.
> > +		 * maps.  Hence, limit to CAP_BPF.
> >   		 */
> >   		return -EPERM;
> I don't think this works, this is pretty much going to break use cases where
> orchestration daemons are deployed as containers that are explicitly granted
> specified cap set and right now this is CAP_SYS_ADMIN and not CAP_BPF for bpf().
> The former needs to be a superset of the latter in order for this to work and
> not break compatibility between kernel upgrades.
> 
> - https://kubernetes.io/docs/tasks/configure-pod-container/security-context/#set-capabilities-for-a-container
> - https://docs.docker.com/engine/reference/run/#runtime-privilege-and-linux-capabilities

These are the links that showing that k8 can delegates caps.
Are you saying that you know of folks who specifically
delegate cap_sys_admin and cap_net_admin _only_ to a container to run bpf in there?