bpf, sockmap: Test shutdown() correctly exits epoll and recv()=0

When session gracefully shutdowns epoll needs to wake up and any recv()
readers should return 0 not the -EAGAIN they previously returned.

Note we use epoll instead of select to test the epoll wake on shutdown
event as well.
Signed-off-by: John Fastabend <john.fastabend@gmail.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Reviewed-by: Jakub Sitnicki <jakub@cloudflare.com>
Link: https://lore.kernel.org/bpf/20230523025618.113937-12-john.fastabend@gmail.com

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

@@ -2,6 +2,7 @@
 // Copyright (c) 2020 Cloudflare
 #include <error.h>
 #include <netinet/tcp.h>
+#include <sys/epoll.h>
 
 #include "test_progs.h"
 #include "test_skmsg_load_helpers.skel.h"
@@ -9,8 +10,11 @@
 #include "test_sockmap_invalid_update.skel.h"
 #include "test_sockmap_skb_verdict_attach.skel.h"
 #include "test_sockmap_progs_query.skel.h"
+#include "test_sockmap_pass_prog.skel.h"
 #include "bpf_iter_sockmap.skel.h"
 
+#include "sockmap_helpers.h"
+
 #define TCP_REPAIR		19	/* TCP sock is under repair right now */
 
 #define TCP_REPAIR_ON		1
@@ -350,6 +354,62 @@ static void test_sockmap_progs_query(enum bpf_attach_type attach_type)
 	test_sockmap_progs_query__destroy(skel);
 }
 
+#define MAX_EVENTS 10
+static void test_sockmap_skb_verdict_shutdown(void)
+{
+	struct epoll_event ev, events[MAX_EVENTS];
+	int n, err, map, verdict, s, c1, p1;
+	struct test_sockmap_pass_prog *skel;
+	int epollfd;
+	int zero = 0;
+	char b;
+
+	skel = test_sockmap_pass_prog__open_and_load();
+	if (!ASSERT_OK_PTR(skel, "open_and_load"))
+		return;
+
+	verdict = bpf_program__fd(skel->progs.prog_skb_verdict);
+	map = bpf_map__fd(skel->maps.sock_map_rx);
+
+	err = bpf_prog_attach(verdict, map, BPF_SK_SKB_STREAM_VERDICT, 0);
+	if (!ASSERT_OK(err, "bpf_prog_attach"))
+		goto out;
+
+	s = socket_loopback(AF_INET, SOCK_STREAM);
+	if (s < 0)
+		goto out;
+	err = create_pair(s, AF_INET, SOCK_STREAM, &c1, &p1);
+	if (err < 0)
+		goto out;
+
+	err = bpf_map_update_elem(map, &zero, &c1, BPF_NOEXIST);
+	if (err < 0)
+		goto out_close;
+
+	shutdown(p1, SHUT_WR);
+
+	ev.events = EPOLLIN;
+	ev.data.fd = c1;
+
+	epollfd = epoll_create1(0);
+	if (!ASSERT_GT(epollfd, -1, "epoll_create(0)"))
+		goto out_close;
+	err = epoll_ctl(epollfd, EPOLL_CTL_ADD, c1, &ev);
+	if (!ASSERT_OK(err, "epoll_ctl(EPOLL_CTL_ADD)"))
+		goto out_close;
+	err = epoll_wait(epollfd, events, MAX_EVENTS, -1);
+	if (!ASSERT_EQ(err, 1, "epoll_wait(fd)"))
+		goto out_close;
+
+	n = recv(c1, &b, 1, SOCK_NONBLOCK);
+	ASSERT_EQ(n, 0, "recv_timeout(fin)");
+out_close:
+	close(c1);
+	close(p1);
+out:
+	test_sockmap_pass_prog__destroy(skel);
+}
+
 void test_sockmap_basic(void)
 {
 	if (test__start_subtest("sockmap create_update_free"))
@@ -384,4 +444,6 @@ void test_sockmap_basic(void)
 		test_sockmap_progs_query(BPF_SK_SKB_STREAM_VERDICT);
 	if (test__start_subtest("sockmap skb_verdict progs query"))
 		test_sockmap_progs_query(BPF_SK_SKB_VERDICT);
+	if (test__start_subtest("sockmap skb_verdict shutdown"))
+		test_sockmap_skb_verdict_shutdown();
 }

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

+#include <linux/bpf.h>
+#include <bpf/bpf_helpers.h>
+#include <bpf/bpf_endian.h>
+
+struct {
+	__uint(type, BPF_MAP_TYPE_SOCKMAP);
+	__uint(max_entries, 20);
+	__type(key, int);
+	__type(value, int);
+} sock_map_rx SEC(".maps");
+
+struct {
+	__uint(type, BPF_MAP_TYPE_SOCKMAP);
+	__uint(max_entries, 20);
+	__type(key, int);
+	__type(value, int);
+} sock_map_tx SEC(".maps");
+
+struct {
+	__uint(type, BPF_MAP_TYPE_SOCKMAP);
+	__uint(max_entries, 20);
+	__type(key, int);
+	__type(value, int);
+} sock_map_msg SEC(".maps");
+
+SEC("sk_skb")
+int prog_skb_verdict(struct __sk_buff *skb)
+{
+	return SK_PASS;
+}
+
+char _license[] SEC("license") = "GPL";