selftests/bpf: Test BPF_CGROUP_INET_SOCK_RELEASE

Simple test that enforces a single SOCK_DGRAM socket per cgroup.
Signed-off-by: Stanislav Fomichev <sdf@google.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Andrii Nakryiko <andriin@fb.com>
Link: https://lore.kernel.org/bpf/20200706230128.4073544-5-sdf@google.com

tools/testing/selftests/bpf/prog_tests/udp_limit.c

+// SPDX-License-Identifier: GPL-2.0
+#include <test_progs.h>
+#include "udp_limit.skel.h"
+
+#include <sys/types.h>
+#include <sys/socket.h>
+
+static int duration;
+
+void test_udp_limit(void)
+{
+	struct udp_limit *skel;
+	int fd1 = -1, fd2 = -1;
+	int cgroup_fd;
+
+	cgroup_fd = test__join_cgroup("/udp_limit");
+	if (CHECK(cgroup_fd < 0, "cg-join", "errno %d", errno))
+		return;
+
+	skel = udp_limit__open_and_load();
+	if (CHECK(!skel, "skel-load", "errno %d", errno))
+		goto close_cgroup_fd;
+
+	skel->links.sock = bpf_program__attach_cgroup(skel->progs.sock, cgroup_fd);
+	skel->links.sock_release = bpf_program__attach_cgroup(skel->progs.sock_release, cgroup_fd);
+	if (CHECK(IS_ERR(skel->links.sock) || IS_ERR(skel->links.sock_release),
+		  "cg-attach", "sock %ld sock_release %ld",
+		  PTR_ERR(skel->links.sock),
+		  PTR_ERR(skel->links.sock_release)))
+		goto close_skeleton;
+
+	/* BPF program enforces a single UDP socket per cgroup,
+	 * verify that.
+	 */
+	fd1 = socket(AF_INET, SOCK_DGRAM, 0);
+	if (CHECK(fd1 < 0, "fd1", "errno %d", errno))
+		goto close_skeleton;
+
+	fd2 = socket(AF_INET, SOCK_DGRAM, 0);
+	if (CHECK(fd2 >= 0, "fd2", "errno %d", errno))
+		goto close_skeleton;
+
+	/* We can reopen again after close. */
+	close(fd1);
+	fd1 = -1;
+
+	fd1 = socket(AF_INET, SOCK_DGRAM, 0);
+	if (CHECK(fd1 < 0, "fd1-again", "errno %d", errno))
+		goto close_skeleton;
+
+	/* Make sure the program was invoked the expected
+	 * number of times:
+	 * - open fd1           - BPF_CGROUP_INET_SOCK_CREATE
+	 * - attempt to openfd2 - BPF_CGROUP_INET_SOCK_CREATE
+	 * - close fd1          - BPF_CGROUP_INET_SOCK_RELEASE
+	 * - open fd1 again     - BPF_CGROUP_INET_SOCK_CREATE
+	 */
+	if (CHECK(skel->bss->invocations != 4, "bss-invocations",
+		  "invocations=%d", skel->bss->invocations))
+		goto close_skeleton;
+
+	/* We should still have a single socket in use */
+	if (CHECK(skel->bss->in_use != 1, "bss-in_use",
+		  "in_use=%d", skel->bss->in_use))
+		goto close_skeleton;
+
+close_skeleton:
+	if (fd1 >= 0)
+		close(fd1);
+	if (fd2 >= 0)
+		close(fd2);
+	udp_limit__destroy(skel);
+close_cgroup_fd:
+	close(cgroup_fd);
+}

tools/testing/selftests/bpf/progs/udp_limit.c

+// SPDX-License-Identifier: GPL-2.0-only
+
+#include <sys/socket.h>
+#include <linux/bpf.h>
+#include <bpf/bpf_helpers.h>
+
+int invocations = 0, in_use = 0;
+
+SEC("cgroup/sock_create")
+int sock(struct bpf_sock *ctx)
+{
+	__u32 key;
+
+	if (ctx->type != SOCK_DGRAM)
+		return 1;
+
+	__sync_fetch_and_add(&invocations, 1);
+
+	if (in_use > 0) {
+		/* BPF_CGROUP_INET_SOCK_RELEASE is _not_ called
+		 * when we return an error from the BPF
+		 * program!
+		 */
+		return 0;
+	}
+
+	__sync_fetch_and_add(&in_use, 1);
+	return 1;
+}
+
+SEC("cgroup/sock_release")
+int sock_release(struct bpf_sock *ctx)
+{
+	__u32 key;
+
+	if (ctx->type != SOCK_DGRAM)
+		return 1;
+
+	__sync_fetch_and_add(&invocations, 1);
+	__sync_fetch_and_add(&in_use, -1);
+	return 1;
+}