net: dsa: refuse cross-chip mirroring operations

In case of a tc mirred action from one switch to another, the behavior
is not correct. We simply tell the source switch driver to program a
mirroring entry towards mirror->to_local_port = to_dp->index, but it is
not even guaranteed that the to_dp belongs to the same switch as dp.

For proper cross-chip support, we would need to go through the
cross-chip notifier layer in switch.c, program the entry on cascade
ports, and introduce new, explicit API for cross-chip mirroring, given
that intermediary switches should have introspection into the DSA tags
passed through the cascade port (and not just program a port mirror on
the entire cascade port). None of that exists today.

Reject what is not implemented so that user space is not misled into
thinking it works.

Fixes: f50f212749e8 ("net: dsa: Add plumbing for port mirroring")
Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.com>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Link: https://patch.msgid.link/20241008094320.3340980-1-vladimir.oltean@nxp.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

diff --git a/net/dsa/user.c b/net/dsa/user.c
index 74eda9b30608e65c8c1c0afe965b5b4d589ea7e0..64f660d2334b77fa97e7d6d586a021d63ac5f6e2 100644 (file)
--- a/net/dsa/user.c
+++ b/net/dsa/user.c
@@ -1392,6 +1392,14 @@ dsa_user_add_cls_matchall_mirred(struct net_device *dev,
        if (!dsa_user_dev_check(act->dev))
                return -EOPNOTSUPP;
 
+       to_dp = dsa_user_to_port(act->dev);
+
+       if (dp->ds != to_dp->ds) {
+               NL_SET_ERR_MSG_MOD(extack,
+                                  "Cross-chip mirroring not implemented");
+               return -EOPNOTSUPP;
+       }
+
        mall_tc_entry = kzalloc(sizeof(*mall_tc_entry), GFP_KERNEL);
        if (!mall_tc_entry)
                return -ENOMEM;
@@ -1399,9 +1407,6 @@ dsa_user_add_cls_matchall_mirred(struct net_device *dev,
        mall_tc_entry->cookie = cls->cookie;
        mall_tc_entry->type = DSA_PORT_MALL_MIRROR;
        mirror = &mall_tc_entry->mirror;
-
-       to_dp = dsa_user_to_port(act->dev);
-
        mirror->to_local_port = to_dp->index;
        mirror->ingress = ingress;