netdev - Re: netns_id in bpf_sk_lookup

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Date:   Mon, 19 Nov 2018 11:47:19 -0800
From:   Joe Stringer <joe@...d.net.nz>
To:     David Ahern <dsahern@...il.com>
Cc:     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 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?