selftests/bpf: Add a selftest for the tracing bpf_get_socket_cookie

This builds up on the existing socket cookie test which checks whether
the bpf_get_socket_cookie helpers provide the same value in
cgroup/connect6 and sockops programs for a socket created by the
userspace part of the test.

Instead of having an update_cookie sockops program tag a socket local
storage with 0xFF, this uses both an update_cookie_sockops program and
an update_cookie_tracing program which succesively tag the socket with
0x0F and then 0xF0.

Signed-off-by: Florent Revest <revest@chromium.org>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: KP Singh <kpsingh@kernel.org>
Link: https://lore.kernel.org/bpf/20210210111406.785541-5-revest@chromium.org

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

@@ -35,9 +35,14 @@ void test_socket_cookie(void)
 	if (!ASSERT_OK_PTR(skel->links.set_cookie, "prog_attach"))
 		goto close_cgroup_fd;
 
-	skel->links.update_cookie = bpf_program__attach_cgroup(
-		skel->progs.update_cookie, cgroup_fd);
-	if (!ASSERT_OK_PTR(skel->links.update_cookie, "prog_attach"))
+	skel->links.update_cookie_sockops = bpf_program__attach_cgroup(
+		skel->progs.update_cookie_sockops, cgroup_fd);
+	if (!ASSERT_OK_PTR(skel->links.update_cookie_sockops, "prog_attach"))
+		goto close_cgroup_fd;
+
+	skel->links.update_cookie_tracing = bpf_program__attach(
+		skel->progs.update_cookie_tracing);
+	if (!ASSERT_OK_PTR(skel->links.update_cookie_tracing, "prog_attach"))
 		goto close_cgroup_fd;
 
 	server_fd = start_server(AF_INET6, SOCK_STREAM, "::1", 0, 0);

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

@@ -5,6 +5,7 @@
 
 #include <bpf/bpf_helpers.h>
 #include <bpf/bpf_endian.h>
+#include <bpf/bpf_tracing.h>
 
 #define AF_INET6 10
 
@@ -20,6 +21,14 @@ struct {
 	__type(value, struct socket_cookie);
 } socket_cookies SEC(".maps");
 
+/*
+ * These three programs get executed in a row on connect() syscalls. The
+ * userspace side of the test creates a client socket, issues a connect() on it
+ * and then checks that the local storage associated with this socket has:
+ * cookie_value == local_port << 8 | 0xFF
+ * The different parts of this cookie_value are appended by those hooks if they
+ * all agree on the output of bpf_get_socket_cookie().
+ */
 SEC("cgroup/connect6")
 int set_cookie(struct bpf_sock_addr *ctx)
 {
@@ -33,14 +42,14 @@ int set_cookie(struct bpf_sock_addr *ctx)
 	if (!p)
 		return 1;
 
-	p->cookie_value = 0xFF;
+	p->cookie_value = 0xF;
 	p->cookie_key = bpf_get_socket_cookie(ctx);
 
 	return 1;
 }
 
 SEC("sockops")
-int update_cookie(struct bpf_sock_ops *ctx)
+int update_cookie_sockops(struct bpf_sock_ops *ctx)
 {
 	struct bpf_sock *sk = ctx->sk;
 	struct socket_cookie *p;
@@ -61,9 +70,30 @@ int update_cookie(struct bpf_sock_ops *ctx)
 	if (p->cookie_key != bpf_get_socket_cookie(ctx))
 		return 1;
 
-	p->cookie_value = (ctx->local_port << 8) | p->cookie_value;
+	p->cookie_value |= (ctx->local_port << 8);
 
 	return 1;
 }
 
+SEC("fexit/inet_stream_connect")
+int BPF_PROG(update_cookie_tracing, struct socket *sock,
+	     struct sockaddr *uaddr, int addr_len, int flags)
+{
+	struct socket_cookie *p;
+
+	if (uaddr->sa_family != AF_INET6)
+		return 0;
+
+	p = bpf_sk_storage_get(&socket_cookies, sock->sk, 0, 0);
+	if (!p)
+		return 0;
+
+	if (p->cookie_key != bpf_get_socket_cookie(sock->sk))
+		return 0;
+
+	p->cookie_value |= 0xF0;
+
+	return 0;
+}
+
 char _license[] SEC("license") = "GPL";