netdev - Re: [PATCH bpf-next v3 2/2] selftests/bpf: verify that rebinding to port

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Date:   Tue, 26 Jan 2021 10:18:38 -0800
From:   Martin KaFai Lau <kafai@...com>
To:     Stanislav Fomichev <sdf@...gle.com>
CC:     <netdev@...r.kernel.org>, <bpf@...r.kernel.org>, <ast@...nel.org>,
        <daniel@...earbox.net>, Andrey Ignatov <rdna@...com>
Subject: Re: [PATCH bpf-next v3 2/2] selftests/bpf: verify that rebinding to
 port < 1024 from BPF works

On Tue, Jan 26, 2021 at 08:51:04AM -0800, Stanislav Fomichev wrote:
> Return 3 to indicate that permission check for port 111
> should be skipped.
> 

[ ... ]

> +void cap_net_bind_service(cap_flag_value_t flag)
> +{
> +	const cap_value_t cap_net_bind_service = CAP_NET_BIND_SERVICE;
> +	cap_t caps;
> +
> +	caps = cap_get_proc();
> +	if (CHECK(!caps, "cap_get_proc", "errno %d", errno))
> +		goto free_caps;
> +
> +	if (CHECK(cap_set_flag(caps, CAP_EFFECTIVE, 1, &cap_net_bind_service,
> +			       flag),
> +		  "cap_set_flag", "errno %d", errno))
> +		goto free_caps;
> +
> +	if (CHECK(cap_set_proc(caps), "cap_set_proc", "errno %d", errno))
> +		goto free_caps;
> +
> +free_caps:
> +	if (CHECK(cap_free(caps), "cap_free", "errno %d", errno))
> +		goto free_caps;
Also mentioned in v2, there is a loop.

> +}
> +
> +void test_bind_perm(void)
> +{
> +	struct bind_perm *skel;
> +	int cgroup_fd;
> +
> +	cgroup_fd = test__join_cgroup("/bind_perm");
> +	if (CHECK(cgroup_fd < 0, "cg-join", "errno %d", errno))
> +		return;
> +
> +	skel = bind_perm__open_and_load();
> +	if (!ASSERT_OK_PTR(skel, "skel"))
> +		goto close_cgroup_fd;
> +
> +	skel->links.bind_v4_prog = bpf_program__attach_cgroup(skel->progs.bind_v4_prog, cgroup_fd);
> +	if (!ASSERT_OK_PTR(skel, "bind_v4_prog"))
> +		goto close_skeleton;
> +
> +	cap_net_bind_service(CAP_CLEAR);
> +	try_bind(110, EACCES);
> +	try_bind(111, 0);
> +	cap_net_bind_service(CAP_SET);
Instead of always CAP_SET at the end of the test,
it is better to do a cap_get_flag() to save the original value
at the beginning of the test and restore it at the end
of the test.