[PATCH rdma-next v1 2/2] RDMA/cma: accept cross-NIC same-host local dst in validate_ipv6_net_dev

[Alex Timofeyev <sashka@ankey.net>]

validate_ipv6_net_dev() confirms an incoming CM REQ was delivered on the
correct net_dev with an rt6_lookup() that requires
rt->rt6i_idev->dev == net_dev. For an IPv6 destination that is local to a
different netdev of the same host, the FIB resolves the lookup onto the
loopback netdev, so rt6i_idev->dev is lo regardless of which physical
netdev owns the listener address. The strict comparison then rejects the
REQ with -EHOSTUNREACH even though it was correctly delivered on net_dev.

Accept the request when the resolved route is RTF_LOCAL and net_dev itself
owns the address the listener was bound to (src_addr). This is the
receive-side counterpart to the cross-NIC same-host send-side fix in
addr_resolve_neigh().

Fixes: f887f2ac87c2 ("IB/cma: Validate routing of incoming requests")
Cc: stable@vger.kernel.org
Cc: Parav Pandit <parav@nvidia.com>
Signed-off-by: Alex Timofeyev <sashka@ankey.net>
---
 drivers/infiniband/core/cma.c | 15 ++++++++++++++-
 1 file changed, 14 insertions(+), 1 deletion(-)

diff --git a/drivers/infiniband/core/cma.c b/drivers/infiniband/core/cma.c
index 9480d1a51c11..872c57943362 100644
--- a/drivers/infiniband/core/cma.c
+++ b/drivers/infiniband/core/cma.c
@@ -1635,7 +1635,20 @@ static bool validate_ipv6_net_dev(struct net_device *net_dev,
 	if (!rt)
 		return false;
 
-	ret = rt->rt6i_idev->dev == net_dev;
+	if (rt->rt6i_idev->dev == net_dev) {
+		ret = true;
+	} else if (rt->rt6i_flags & RTF_LOCAL) {
+		/* For a destination that is local to another netdev of the same
+		 * host, the FIB collapses the lookup onto the loopback netdev,
+		 * so rt6i_idev->dev is not net_dev even though the request was
+		 * correctly delivered on net_dev. Accept it when net_dev itself
+		 * owns the address we were listening on.
+		 */
+		ret = ipv6_chk_addr(dev_net(net_dev), &src_addr->sin6_addr,
+				    net_dev, 1);
+	} else {
+		ret = false;
+	}
 	ip6_rt_put(rt);
 
 	return ret;
-- 
2.40.4