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

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Message-Id: <20210121012241.2109147-2-sdf@google.com>
Date:   Wed, 20 Jan 2021 17:22:41 -0800
From:   Stanislav Fomichev <sdf@...gle.com>
To:     netdev@...r.kernel.org, bpf@...r.kernel.org
Cc:     ast@...nel.org, daniel@...earbox.net,
        Stanislav Fomichev <sdf@...gle.com>
Subject: [PATCH bpf-next 2/2] selftests/bpf: verify that rebinding to port <
 1024 from BPF works

BPF rewrites from 111 to 111, but it still should mark the port as
"changed".
We also verify that if port isn't touched by BPF, it's still prohibited.

Signed-off-by: Stanislav Fomichev <sdf@...gle.com>
---
 .../selftests/bpf/prog_tests/bind_perm.c      | 88 +++++++++++++++++++
 tools/testing/selftests/bpf/progs/bind_perm.c | 36 ++++++++
 2 files changed, 124 insertions(+)
 create mode 100644 tools/testing/selftests/bpf/prog_tests/bind_perm.c
 create mode 100644 tools/testing/selftests/bpf/progs/bind_perm.c

diff --git a/tools/testing/selftests/bpf/prog_tests/bind_perm.c b/tools/testing/selftests/bpf/prog_tests/bind_perm.c
new file mode 100644
index 000000000000..840a04ac9042
--- /dev/null
+++ b/tools/testing/selftests/bpf/prog_tests/bind_perm.c
@@ -0,0 +1,88 @@
+// SPDX-License-Identifier: GPL-2.0
+#include <test_progs.h>
+#include "bind_perm.skel.h"
+
+#include <sys/types.h>
+#include <sys/socket.h>
+#include <sys/capability.h>
+
+static int duration;
+
+void try_bind(int port, int expected_errno)
+{
+	struct sockaddr_in sin = {};
+	int fd = -1;
+
+	fd = socket(AF_INET, SOCK_STREAM, 0);
+	if (CHECK(fd < 0, "fd", "errno %d", errno))
+		goto close_socket;
+
+	sin.sin_family = AF_INET;
+	sin.sin_port = htons(port);
+
+	errno = 0;
+	bind(fd, (struct sockaddr *)&sin, sizeof(sin));
+	CHECK(errno != expected_errno, "bind", "errno %d, expected %d",
+	      errno, expected_errno);
+
+close_socket:
+	if (fd >= 0)
+		close(fd);
+}
+
+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,
+			       CAP_CLEAR),
+		  "cap_set_flag", "errno %d", errno))
+		goto free_caps;
+
+	if (CHECK(cap_set_flag(caps, CAP_EFFECTIVE, 1, &cap_net_bind_service,
+			       CAP_CLEAR),
+		  "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;
+}
+
+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 (CHECK(!skel, "skel-load", "errno %d", errno))
+		goto close_cgroup_fd;
+
+	skel->links.bind_v4_prog = bpf_program__attach_cgroup(skel->progs.bind_v4_prog, cgroup_fd);
+	if (CHECK(IS_ERR(skel->links.bind_v4_prog),
+		  "cg-attach", "bind4 %ld",
+		  PTR_ERR(skel->links.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);
+
+close_skeleton:
+	bind_perm__destroy(skel);
+close_cgroup_fd:
+	close(cgroup_fd);
+}
diff --git a/tools/testing/selftests/bpf/progs/bind_perm.c b/tools/testing/selftests/bpf/progs/bind_perm.c
new file mode 100644
index 000000000000..2194587ec806
--- /dev/null
+++ b/tools/testing/selftests/bpf/progs/bind_perm.c
@@ -0,0 +1,36 @@
+// SPDX-License-Identifier: GPL-2.0
+
+#include <linux/stddef.h>
+#include <linux/bpf.h>
+#include <sys/types.h>
+#include <sys/socket.h>
+#include <bpf/bpf_helpers.h>
+#include <bpf/bpf_endian.h>
+
+SEC("cgroup/bind4")
+int bind_v4_prog(struct bpf_sock_addr *ctx)
+{
+	struct bpf_sock *sk;
+	__u32 user_ip4;
+	__u16 user_port;
+
+	sk = ctx->sk;
+	if (!sk)
+		return 0;
+
+	if (sk->family != AF_INET)
+		return 0;
+
+	if (ctx->type != SOCK_STREAM)
+		return 0;
+
+	/* Rewriting to the same value should still cause
+	 * permission check to be bypassed.
+	 */
+	if (ctx->user_port == bpf_htons(111))
+		ctx->user_port = bpf_htons(111);
+
+	return 1;
+}
+
+char _license[] SEC("license") = "GPL";
-- 
2.30.0.284.gd98b1dd5eaa7-goog