Re: [PATCH 0/5] Return fds from privileged sockhash/sockmap lookup

On Tue, Mar 10, 2020 at 06:47 PM CET, Lorenz Bauer wrote:

We want to use sockhash and sockmap to build the control plane for
our upcoming BPF socket dispatch work. We realised that it's
difficult to resize or otherwise rebuild these maps if needed,
because there is no way to get at their contents. This patch set
allows a privileged user to retrieve fds from these map types,
which removes this obstacle.

Since it takes just a few lines of code to get an FD for a sock:

	fd = get_unused_fd_flags(O_CLOEXEC);
	if (unlikely(fd < 0))
		return fd;
        fd_install(fd, get_file(sk->sk_socket->file));

... I can't help but wonder where's the catch?

IOW, why wasn't this needed so far?
How does Cilium avoid resizing & rebuilding sockmaps?

Just asking out of curiosity.

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