netdev - Re: netns_id in bpf_sk_lookup

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Date:   Mon, 19 Nov 2018 12:54:42 -0800
From:   Joe Stringer <joe@...d.net.nz>
To:     nicolas.dichtel@...nd.com
Cc:     David Ahern <dsahern@...il.com>, Joe Stringer <joe@...d.net.nz>,
        netdev <netdev@...r.kernel.org>, daniel@...earbox.net
Subject: Re: netns_id in bpf_sk_lookup_{tcp,udp}

On Mon, 19 Nov 2018 at 12:29, Nicolas Dichtel <nicolas.dichtel@...nd.com> wrote:
>
> Le 19/11/2018 à 20:54, David Ahern a écrit :
> > On 11/19/18 12:47 PM, Joe Stringer wrote:
> >> On Mon, 19 Nov 2018 at 10:39, David Ahern <dsahern@...il.com> wrote:
> >>>
> >>> On 11/19/18 11:36 AM, Joe Stringer wrote:
> >>>> Hi David, thanks for pointing this out.
> >>>>
> >>>> This is more of an oversight through iterations, the runtime lookup
> >>>> will fail to find a socket if the netns value is greater than the
> >>>> range of a uint32 so I think it would actually make more sense to drop
> >>>> the parameter size to u32 rather than u64 so that this would be
> >>>> validated at load time rather than silently returning NULL because of
> >>>> a bad parameter.
> >>>
> >>> ok. I was wondering if it was a u64 to handle nsid of 0 which as I
> >>> understand it is a legal nsid. If you drop to u32, how do you know when
> >>> nsid has been set?
> >>
> >> I was operating under the assumption that 0 represents the root netns
> >> id, and cannot be assigned to another non-root netns.
> >>
> >> Looking at __peernet2id_alloc(), it seems to me like it attempts to
> >> find a netns and if it cannot find one, returns 0, which then leads to
> >> a scroll over the idr starting from 0 to INT_MAX to find a legitimate
> >> id for the netns, so I think this is a fair assumption?
> The NET_ID_ZERO trick is used to manage nsid 0 in net_eq_idr() (idr_for_each()
> stops when the callback returns != 0).
>
> >>
> >
> > Maybe Nicolas can give a definitive answer; as I recall he added the
> > NSID option. I have not had time to walk the code. But I do recall
> > seeing an id of 0. e.g, on my dev box:
> > $ ip netns
> > vms (id: 0)
> >
> > And include/uapi/linux/net_namespace.h shows -1 as not assigned.
> Yes, 0 is a valid value and can be assigned to any netns.
> nsid are signed 32 bit values. Note that -1 (NETNSA_NSID_NOT_ASSIGNED) is used
> by the kernel to express that the nsid is not assigned. It can also be used by
> the user to let the kernel chooses a nsid.
>
> $ ip netns add foo
> $ ip netns add bar
> $ ip netns
> bar
> foo
> $ ip netns set foo 0
> $ ip netns set bar auto
> $ ip netns
> bar (id: 1)
> foo (id: 0)

OK, I'll fix this up then.