selftests: mptcp: sockopt: relax expected returned size

Selftests are supposed to run on any kernels, including the old ones not
supporting all MPTCP features.

One of them is the getsockopt(SOL_MPTCP) to get info about the MPTCP
connections introduced by commit 55c42fa7 ("mptcp: add MPTCP_INFO
getsockopt") and the following ones.

We cannot guess in advance which sizes the kernel will returned: older
kernel can returned smaller sizes, e.g. recently the tcp_info structure
has been modified in commit 71fc7047 ("tcp: add rcv_wnd and
plb_rehash to TCP_INFO") where a new field has been added.

The userspace can also expect a smaller size if it is compiled with old
uAPI kernel headers.

So for these sizes, we can only check if they are above a certain
threshold, 0 for the moment. We can also only compared sizes with the
ones set by the kernel.

Link: https://github.com/multipath-tcp/mptcp_net-next/issues/368
Fixes: ce997912 ("selftests: mptcp: add mptcp getsockopt test cases")
Cc: stable@vger.kernel.org
Signed-off-by: Matthieu Baerts <matthieu.baerts@tessares.net>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

tools/testing/selftests/net/mptcp/mptcp_sockopt.c

@@ -87,6 +87,10 @@ struct so_state {
 	uint64_t tcpi_rcv_delta;
 };
 
+#ifndef MIN
+#define MIN(a, b) ((a) < (b) ? (a) : (b))
+#endif
+
 static void die_perror(const char *msg)
 {
 	perror(msg);
@@ -349,13 +353,14 @@ static void do_getsockopt_tcp_info(struct so_state *s, int fd, size_t r, size_t
 			xerror("getsockopt MPTCP_TCPINFO (tries %d, %m)");
 
 		assert(olen <= sizeof(ti));
-		assert(ti.d.size_user == ti.d.size_kernel);
-		assert(ti.d.size_user == sizeof(struct tcp_info));
+		assert(ti.d.size_kernel > 0);
+		assert(ti.d.size_user ==
+		       MIN(ti.d.size_kernel, sizeof(struct tcp_info)));
 		assert(ti.d.num_subflows == 1);
 
 		assert(olen > (socklen_t)sizeof(struct mptcp_subflow_data));
 		olen -= sizeof(struct mptcp_subflow_data);
-		assert(olen == sizeof(struct tcp_info));
+		assert(olen == ti.d.size_user);
 
 		if (ti.ti[0].tcpi_bytes_sent == w &&
 		    ti.ti[0].tcpi_bytes_received == r)
@@ -401,13 +406,14 @@ static void do_getsockopt_subflow_addrs(int fd)
 		die_perror("getsockopt MPTCP_SUBFLOW_ADDRS");
 
 	assert(olen <= sizeof(addrs));
-	assert(addrs.d.size_user == addrs.d.size_kernel);
-	assert(addrs.d.size_user == sizeof(struct mptcp_subflow_addrs));
+	assert(addrs.d.size_kernel > 0);
+	assert(addrs.d.size_user ==
+	       MIN(addrs.d.size_kernel, sizeof(struct mptcp_subflow_addrs)));
 	assert(addrs.d.num_subflows == 1);
 
 	assert(olen > (socklen_t)sizeof(struct mptcp_subflow_data));
 	olen -= sizeof(struct mptcp_subflow_data);
-	assert(olen == sizeof(struct mptcp_subflow_addrs));
+	assert(olen == addrs.d.size_user);
 
 	llen = sizeof(local);
 	ret = getsockname(fd, (struct sockaddr *)&local, &llen);