[PATCH net v2 2/3] selftest/bpf: Add test for AF_VSOCK connect() racing sockmap update

[Michal Luczaj <mhal@rbox.co>]

Racing signal-interrupted connect() and sockmap update may result in an
unconnected (and missing vsock transport) socket in a sockmap.

Test spends 2 seconds attempting to reach WARN_ON_ONCE().

connect
  / state = SS_CONNECTED /
                                sock_map_update_elem
  if signal_pending
    state = SS_UNCONNECTED

connect
  transport = NULL
                                vsock_bpf_recvmsg
                                  WARN_ON_ONCE(!vsk->transport)

Signed-off-by: Michal Luczaj <mhal@rbox.co>
---
 .../selftests/bpf/prog_tests/sockmap_basic.c       | 111 +++++++++++++++++++++
 1 file changed, 111 insertions(+)

diff --git a/tools/testing/selftests/bpf/prog_tests/sockmap_basic.c b/tools/testing/selftests/bpf/prog_tests/sockmap_basic.c
index 1e3e4392dcca0e1722c1982ecc649a80c27443b2..5c278353a924294a1452f650634cec0539804b1a 100644
--- a/tools/testing/selftests/bpf/prog_tests/sockmap_basic.c
+++ b/tools/testing/selftests/bpf/prog_tests/sockmap_basic.c
@@ -3,6 +3,7 @@
 #include <error.h>
 #include <netinet/tcp.h>
 #include <sys/epoll.h>
+#include <linux/time64.h>
 
 #include "test_progs.h"
 #include "test_skmsg_load_helpers.skel.h"
@@ -1042,6 +1043,114 @@ static void test_sockmap_vsock_unconnected(void)
 	xclose(map);
 }
 
+#define CONNECT_SIGNAL_RACE_TIMEOUT 2 /* seconds */
+
+static void sig_handler(int signum)
+{
+	/* nop */
+}
+
+static void connect_signal_racer_cleanup(void *map)
+{
+	xclose(*(int *)map);
+}
+
+static void *connect_signal_racer(void *arg)
+{
+	int map;
+
+	map = bpf_map_create(BPF_MAP_TYPE_SOCKMAP, NULL, sizeof(int),
+			     sizeof(int), 1, NULL);
+	if (!ASSERT_OK_FD(map, "bpf_map_create"))
+		return NULL;
+
+	pthread_cleanup_push(connect_signal_racer_cleanup, &map);
+
+	for (;;) {
+		int c = *(int *)arg;
+		int zero = 0;
+
+		(void)bpf_map_update_elem(map, &zero, &c, BPF_ANY);
+
+		if (kill(0, SIGUSR1)) {
+			FAIL_ERRNO("kill");
+			break;
+		}
+
+		pthread_testcancel();
+	}
+
+	pthread_cleanup_pop(1);
+
+	return NULL;
+}
+
+static void test_sockmap_vsock_connect_signal_race(void)
+{
+	struct sockaddr_vm addr = {
+		.svm_family = AF_VSOCK,
+		.svm_cid = VMADDR_CID_LOCAL,
+		.svm_port = VMADDR_PORT_ANY
+	};
+	struct sockaddr_vm bad_addr;
+	sighandler_t orig_handler;
+	pthread_t thread;
+	socklen_t alen;
+	int s, c, p;
+	__u64 tout;
+
+	orig_handler = signal(SIGUSR1, sig_handler);
+	if (!ASSERT_NEQ(orig_handler, SIG_ERR, "signal handler setup"))
+		return;
+
+	s = socket_loopback(AF_VSOCK, SOCK_SEQPACKET | SOCK_NONBLOCK);
+	if (s < 0)
+		goto restore;
+
+	alen = sizeof(addr);
+	if (xgetsockname(s, (struct sockaddr *)&addr, &alen) < 0)
+		goto close;
+
+	bad_addr = addr;
+	bad_addr.svm_cid = 0x42424242; /* non-existing */
+
+	if (xpthread_create(&thread, 0, connect_signal_racer, &c))
+		goto close;
+
+	tout = get_time_ns() + CONNECT_SIGNAL_RACE_TIMEOUT * NSEC_PER_SEC;
+	do {
+		c = xsocket(AF_VSOCK, SOCK_SEQPACKET, 0);
+		if (c < 0)
+			break;
+
+		if (!connect(c, (struct sockaddr *)&addr, alen) ||
+		    errno != EINTR)
+			goto retry;
+
+		if (!connect(c, (struct sockaddr *)&bad_addr, alen) ||
+		    errno != ESOCKTNOSUPPORT)
+			goto retry;
+
+		if ((recv(c, &(char){0}, 1, MSG_DONTWAIT) < 0) &&
+		    errno == ENODEV) {
+			FAIL_ERRNO("recv");
+			tout = 0;
+		}
+retry:
+		xclose(c);
+		p = accept(s, NULL, NULL);
+		if (p >= 0)
+			xclose(p);
+	} while (get_time_ns() < tout);
+
+	ASSERT_OK(pthread_cancel(thread), "pthread_cancel");
+	xpthread_join(thread, NULL);
+close:
+	xclose(s);
+restore:
+	ASSERT_NEQ(signal(SIGUSR1, orig_handler), SIG_ERR, "handler restore");
+}
+
 void test_sockmap_basic(void)
 {
 	if (test__start_subtest("sockmap create_update_free"))
@@ -1108,4 +1217,6 @@ void test_sockmap_basic(void)
 		test_sockmap_skb_verdict_vsock_poll();
 	if (test__start_subtest("sockmap vsock unconnected"))
 		test_sockmap_vsock_unconnected();
+	if (test__start_subtest("sockmap vsock connect signal race"))
+		test_sockmap_vsock_connect_signal_race();
 }

-- 
2.48.1