linux-kernel - Re: [PATCH bpf-next v3 1/4] bpf: sock ops: add netns ino and dev in bpf context

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Date:   Sat, 27 Apr 2019 11:39:40 -0700
From:   Jakub Kicinski <jakub.kicinski@...ronome.com>
To:     Alban Crequy <alban@...volk.io>
Cc:     Alban Crequy <alban.crequy@...il.com>,
        John Fastabend <john.fastabend@...il.com>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        bpf <bpf@...r.kernel.org>, netdev <netdev@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Iago López Galeiras <iago@...volk.io>
Subject: Re: [PATCH bpf-next v3 1/4] bpf: sock ops: add netns ino and dev in
 bpf context

On Sat, 27 Apr 2019 12:48:25 +0200, Alban Crequy wrote:
> On Fri, Apr 26, 2019 at 11:03 PM Jakub Kicinski
> <jakub.kicinski@...ronome.com> wrote:
> >
> > On Fri, 26 Apr 2019 17:48:45 +0200, Alban Crequy wrote:  
> > > In the unlikely case where network namespaces are not compiled in
> > > (CONFIG_NET_NS=n), the verifier will not allow access to ->netns_*.  
> >
> > Naive question - why return an error?  init_net should always be there,
> > no?  
> 
> True for netns_dev. However, without CONFIG_NET_NS, we cannot access netns_ino:
> 
> (struct sock_common).possible_net_t.(struct net *):
> 
> typedef struct {
> #ifdef CONFIG_NET_NS
>         struct net *net;
> #endif
> } possible_net_t;
> 
> And I don't think it would make much sense to allow access to
> netns_dev but not netns_ino.

Right, if CONFIG_NET_NS=n we could just take the pointer to init_net
directly, and not worry about the field.  IMHO it'd be preferable to
changing the UAPI based on kernel config, but I don't feel super
strongly.