If an MPTCP socket has been created with AF_INET6 and the IPV6_V6ONLY
option has been set, the userspace PM would allow creating subflows
using IPv4 addresses, e.g. mapped in v6.

The userspace PM will also accept creating subflows with local and
remote addresses having different families resulting in the creation
of non expected subflows.

It is then required to check the given families can be accepted. This is
done by using a new helper for addresses family matching, taking care of
IPv4 vs IPv4-mapped-IPv6 addresses. This helper will be re-used later by
the in-kernel path-manager to use mixed IPv4 and IPv6 addresses.

While at it, a clear error message is now reported if there are some
conflicts with the families that have been passed by the userspace.

Fixes: 702c2f646d42 ("mptcp: netlink: allow userspace-driven subflow establishment")
Signed-off-by: Matthieu Baerts <matthieu.baerts@tessares.net>
---
 net/mptcp/pm.c           | 25 +++++++++++++++++++++++++
 net/mptcp/pm_userspace.c |  7 +++++++
 net/mptcp/protocol.h     |  3 +++
 3 files changed, 35 insertions(+)

diff --git a/net/mptcp/pm.c b/net/mptcp/pm.c
index cdeb7280ac76..083f3f8322c0 100644
--- a/net/mptcp/pm.c
+++ b/net/mptcp/pm.c
@@ -413,6 +413,31 @@ void mptcp_pm_subflow_chk_stale(const struct mptcp_sock *msk, struct sock *ssk)
 	}
 }
 
+/* if sk is ipv4 or ipv6_only allows only same-family local and remote addresses,
+ * otherwise allow any matching local/remote pair
+ */
+bool mptcp_pm_addr_families_match(const struct sock *sk,
+				  const struct mptcp_addr_info *loc,
+				  const struct mptcp_addr_info *rem)
+{
+	bool mptcp_is_v4 = sk->sk_family == AF_INET;
+
+#if IS_ENABLED(CONFIG_MPTCP_IPV6)
+	bool loc_is_v4 = loc->family == AF_INET || ipv6_addr_v4mapped(&loc->addr6);
+	bool rem_is_v4 = rem->family == AF_INET || ipv6_addr_v4mapped(&rem->addr6);
+
+	if (mptcp_is_v4)
+		return loc_is_v4 && rem_is_v4;
+
+	if (ipv6_only_sock(sk))
+		return !loc_is_v4 && !rem_is_v4;
+
+	return loc_is_v4 == rem_is_v4;
+#else
+	return mptcp_is_v4 && loc->family == AF_INET && rem->family && AF_INET;
+#endif
+}
+
 void mptcp_pm_data_reset(struct mptcp_sock *msk)
 {
 	u8 pm_type = mptcp_get_pm_type(sock_net((struct sock *)msk));
diff --git a/net/mptcp/pm_userspace.c b/net/mptcp/pm_userspace.c
index 65dcc55a8ad8..ea6ad9da7493 100644
--- a/net/mptcp/pm_userspace.c
+++ b/net/mptcp/pm_userspace.c
@@ -294,6 +294,13 @@ int mptcp_nl_cmd_sf_create(struct sk_buff *skb, struct genl_info *info)
 	}
 
 	sk = (struct sock *)msk;
+
+	if (!mptcp_pm_addr_families_match(sk, &addr_l, &addr_r)) {
+		GENL_SET_ERR_MSG(info, "families mismatch");
+		err = -EINVAL;
+		goto create_err;
+	}
+
 	lock_sock(sk);
 
 	err = __mptcp_subflow_connect(sk, &addr_l, &addr_r);
diff --git a/net/mptcp/protocol.h b/net/mptcp/protocol.h
index b2b56a80e817..871ec3e93314 100644
--- a/net/mptcp/protocol.h
+++ b/net/mptcp/protocol.h
@@ -793,6 +793,9 @@ int mptcp_pm_parse_addr(struct nlattr *attr, struct genl_info *info,
 int mptcp_pm_parse_entry(struct nlattr *attr, struct genl_info *info,
 			 bool require_family,
 			 struct mptcp_pm_addr_entry *entry);
+bool mptcp_pm_addr_families_match(const struct sock *sk,
+				  const struct mptcp_addr_info *loc,
+				  const struct mptcp_addr_info *rem);
 void mptcp_pm_subflow_chk_stale(const struct mptcp_sock *msk, struct sock *ssk);
 void mptcp_pm_nl_subflow_chk_stale(const struct mptcp_sock *msk, struct sock *ssk);
 void mptcp_pm_new_connection(struct mptcp_sock *msk, const struct sock *ssk, int server_side);
-- 
2.37.2