[PATCH net v2 2/2] selftests: net: Add SO_REUSEPORT bind cache test to bind_wildcard.c

[Juan Agustin Niccolini <juanagusnicco@gmail.com>]

Add a test for the bug fixed by "tcp: Fix the SO_REUSEPORT bind cache
admitting a conflicting socket". With a 0.0.0.0 listener on the port, a
v6only [::] SO_REUSEPORT socket fills the bind cache, and a dual-stack
[::] SO_REUSEPORT socket must then fail to bind with EADDRINUSE.

Without the fix:

  #  RUN           global.reuseport_v6only_cache ...
  # bind_wildcard.c:860:reuseport_v6only_cache:Expected ret (0) == -1 (-1)
  # reuseport_v6only_cache: Test terminated by assertion
  #          FAIL  global.reuseport_v6only_cache
  not ok 1 global.reuseport_v6only_cache

With it:

  #  RUN           global.reuseport_v6only_cache ...
  #            OK  global.reuseport_v6only_cache
  ok 1 global.reuseport_v6only_cache

Signed-off-by: Juan Agustin Niccolini <juanagusnicco@gmail.com>
---
 tools/testing/selftests/net/bind_wildcard.c | 54 +++++++++++++++++++++
 1 file changed, 54 insertions(+)

diff --git a/tools/testing/selftests/net/bind_wildcard.c b/tools/testing/selftests/net/bind_wildcard.c
index be3298c791b2..334a0cf87edf 100644
--- a/tools/testing/selftests/net/bind_wildcard.c
+++ b/tools/testing/selftests/net/bind_wildcard.c
@@ -811,4 +811,58 @@ TEST_F(bind_wildcard, reuseport)
 		bind_socket(_metadata, self, variant, i, SO_REUSEPORT);
 }
 
+/* The SO_REUSEPORT bind cache (tb->fast_*) filled by a v6only [::] socket
+ * must not let a dual-stack [::] socket skip the conflict check against a
+ * 0.0.0.0 listener.
+ */
+TEST(reuseport_v6only_cache)
+{
+	struct sockaddr_in6 addr6 = {
+		.sin6_family = AF_INET6,
+		.sin6_addr = in6addr_any,
+	};
+	struct sockaddr_in addr4 = {
+		.sin_family = AF_INET,
+		.sin_addr.s_addr = htonl(INADDR_ANY),
+	};
+	socklen_t addrlen;
+	int fd[3], ret;
+	int on = 1;
+
+	ASSERT_EQ(unshare(CLONE_NEWNET), 0);
+
+	/* bind(0.0.0.0:P), listen() */
+	fd[0] = socket(AF_INET, SOCK_STREAM, 0);
+	ASSERT_GT(fd[0], 0);
+	ASSERT_EQ(bind(fd[0], (struct sockaddr *)&addr4, sizeof(addr4)), 0);
+	ASSERT_EQ(listen(fd[0], 1), 0);
+
+	addrlen = sizeof(addr4);
+	ASSERT_EQ(getsockname(fd[0], (struct sockaddr *)&addr4, &addrlen), 0);
+	addr6.sin6_port = addr4.sin_port;
+
+	/* SO_REUSEPORT + IPV6_V6ONLY, bind([::]:P) fills the cache. */
+	fd[1] = socket(AF_INET6, SOCK_STREAM, 0);
+	ASSERT_GT(fd[1], 0);
+	ret = setsockopt(fd[1], SOL_IPV6, IPV6_V6ONLY, &on, sizeof(on));
+	ASSERT_EQ(ret, 0);
+	ret = setsockopt(fd[1], SOL_SOCKET, SO_REUSEPORT, &on, sizeof(on));
+	ASSERT_EQ(ret, 0);
+	ASSERT_EQ(bind(fd[1], (struct sockaddr *)&addr6, sizeof(addr6)), 0);
+
+	/* SO_REUSEPORT, bind([::]:P) conflicts with 0.0.0.0:P. */
+	fd[2] = socket(AF_INET6, SOCK_STREAM, 0);
+	ASSERT_GT(fd[2], 0);
+	ret = setsockopt(fd[2], SOL_SOCKET, SO_REUSEPORT, &on, sizeof(on));
+	ASSERT_EQ(ret, 0);
+
+	ret = bind(fd[2], (struct sockaddr *)&addr6, sizeof(addr6));
+	ASSERT_EQ(ret, -1);
+	ASSERT_EQ(errno, EADDRINUSE);
+
+	close(fd[2]);
+	close(fd[1]);
+	close(fd[0]);
+}
+
 TEST_HARNESS_MAIN
-- 
2.43.0