Alexei Starovoitov [off-list ref] writes:

in cases where bpf programs are looking at sockets and packets
that belong to different netns, it could be useful to read netns inode,
so that programs can make intelligent decisions.
For example to disallow raw sockets in all non-init netns the program can do:
if (sk->type == SOCK_RAW && sk->netns_inum != 0xf0000075)
  return 0;
where 0xf0000075 inode comes from /proc/pid/ns/net

Similarly TC cls_bpf/act_bpf and socket filters can do
if (skb->netns_inum == expected_inode)

Nacked-by: "Eric W. Biederman" [off-list ref]

Particularly you need to compare more than the inode number.
Further I have never guaranteed there will be exactly one inode
per network namespace, just that if the device number and the inode
number pair match they are the same.

Beyond that the entire concept is complete rubbish.

The only sane thing is to interpret whatever your bpf program in the
context of the program which installs it.

If you can't do that you have a very broken piece of userspace
interface.  Which appears to be the case here.

Eric