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 55c42fa7fa33 ("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 71fc704768f6 ("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: ce9979129a0b ("selftests: mptcp: add mptcp getsockopt test cases")
Signed-off-by: Matthieu Baerts <matthieu.baerts@tessares.net>
---
v3:
  - size_user: check if it is the min between the user and kernel sizes
---
 tools/testing/selftests/net/mptcp/mptcp_sockopt.c | 16 ++++++++++------
 1 file changed, 10 insertions(+), 6 deletions(-)

diff --git a/tools/testing/selftests/net/mptcp/mptcp_sockopt.c b/tools/testing/selftests/net/mptcp/mptcp_sockopt.c
index 86a378731e8b..de897f77e174 100644
--- a/tools/testing/selftests/net/mptcp/mptcp_sockopt.c
+++ b/tools/testing/selftests/net/mptcp/mptcp_sockopt.c
@@ -123,6 +123,8 @@ struct so_state {
 	bool pkt_stats_avail;
 };
 
+#define MIN(a, b) (((a) < (b)) ? (a) : (b))
+
 static void die_perror(const char *msg)
 {
 	perror(msg);
@@ -386,13 +388,14 @@ 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);
 
 		s->tcp_info = ti.ti[0];
 
@@ -440,13 +443,14 @@ static void do_getsockopt_subflow_addrs(struct so_state *s, 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);

-- 
2.39.2