bpf, sockmap: Test FIONREAD returns correct bytes in rx buffer with drops

When BPF program drops pkts the sockmap logic 'eats' the packet and
updates copied_seq. In the PASS case where the sk_buff is accepted
we update copied_seq from recvmsg path so we need a new test to
handle the drop case.

Original patch series broke this resulting in

test_sockmap_skb_verdict_fionread:PASS:ioctl(FIONREAD) error 0 nsec
test_sockmap_skb_verdict_fionread:FAIL:ioctl(FIONREAD) unexpected ioctl(FIONREAD): actual 1503041772 != expected 256

After updated patch with fix.
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/20230523025618.113937-14-john.fastabend@gmail.com

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

@@ -11,6 +11,7 @@
 #include "test_sockmap_skb_verdict_attach.skel.h"
 #include "test_sockmap_progs_query.skel.h"
 #include "test_sockmap_pass_prog.skel.h"
+#include "test_sockmap_drop_prog.skel.h"
 #include "bpf_iter_sockmap.skel.h"
 
 #include "sockmap_helpers.h"
@@ -410,19 +411,31 @@ static void test_sockmap_skb_verdict_shutdown(void)
 	test_sockmap_pass_prog__destroy(skel);
 }
 
-static void test_sockmap_skb_verdict_fionread(void)
+static void test_sockmap_skb_verdict_fionread(bool pass_prog)
 {
+	int expected, zero = 0, sent, recvd, avail;
 	int err, map, verdict, s, c0, c1, p0, p1;
-	struct test_sockmap_pass_prog *skel;
-	int zero = 0, sent, recvd, avail;
+	struct test_sockmap_pass_prog *pass;
+	struct test_sockmap_drop_prog *drop;
 	char buf[256] = "0123456789";
 
-	skel = test_sockmap_pass_prog__open_and_load();
-	if (!ASSERT_OK_PTR(skel, "open_and_load"))
+	if (pass_prog) {
+		pass = test_sockmap_pass_prog__open_and_load();
+		if (!ASSERT_OK_PTR(pass, "open_and_load"))
 			return;
+		verdict = bpf_program__fd(pass->progs.prog_skb_verdict);
+		map = bpf_map__fd(pass->maps.sock_map_rx);
+		expected = sizeof(buf);
+	} else {
+		drop = test_sockmap_drop_prog__open_and_load();
+		if (!ASSERT_OK_PTR(drop, "open_and_load"))
+			return;
+		verdict = bpf_program__fd(drop->progs.prog_skb_verdict);
+		map = bpf_map__fd(drop->maps.sock_map_rx);
+		/* On drop data is consumed immediately and copied_seq inc'd */
+		expected = 0;
+	}
 
-	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"))
@@ -443,9 +456,12 @@ static void test_sockmap_skb_verdict_fionread(void)
 	ASSERT_EQ(sent, sizeof(buf), "xsend(p0)");
 	err = ioctl(c1, FIONREAD, &avail);
 	ASSERT_OK(err, "ioctl(FIONREAD) error");
-	ASSERT_EQ(avail, sizeof(buf), "ioctl(FIONREAD)");
+	ASSERT_EQ(avail, expected, "ioctl(FIONREAD)");
+	/* On DROP test there will be no data to read */
+	if (pass_prog) {
 		recvd = recv_timeout(c1, &buf, sizeof(buf), SOCK_NONBLOCK, IO_TIMEOUT_SEC);
 		ASSERT_EQ(recvd, sizeof(buf), "recv_timeout(c0)");
+	}
 
 out_close:
 	close(c0);
@@ -453,7 +469,10 @@ static void test_sockmap_skb_verdict_fionread(void)
 	close(c1);
 	close(p1);
 out:
-	test_sockmap_pass_prog__destroy(skel);
+	if (pass_prog)
+		test_sockmap_pass_prog__destroy(pass);
+	else
+		test_sockmap_drop_prog__destroy(drop);
 }
 
 void test_sockmap_basic(void)
@@ -493,5 +512,7 @@ void test_sockmap_basic(void)
 	if (test__start_subtest("sockmap skb_verdict shutdown"))
 		test_sockmap_skb_verdict_shutdown();
 	if (test__start_subtest("sockmap skb_verdict fionread"))
-		test_sockmap_skb_verdict_fionread();
+		test_sockmap_skb_verdict_fionread(true);
+	if (test__start_subtest("sockmap skb_verdict fionread on drop"))
+		test_sockmap_skb_verdict_fionread(false);
 }

tools/testing/selftests/bpf/progs/test_sockmap_drop_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_DROP;
+}
+
+char _license[] SEC("license") = "GPL";