net: dsa: tag_sja1105: fix source port decoding in vlan_filtering=0 bridge mode

There was a regression introduced by the blamed commit, where pinging to
a VLAN-unaware bridge would fail with the repeated message "Couldn't
decode source port" coming from the tagging protocol driver.

When receiving packets with a bridge_vid as determined by
dsa_tag_8021q_bridge_join(), dsa_8021q_rcv() will decode:
- source_port = 0 (which isn't really valid, more like "don't know")
- switch_id = 0 (which isn't really valid, more like "don't know")
- vbid = value in range 1-7

Since the blamed patch has reversed the order of the checks, we are now
going to believe that source_port != -1 and switch_id != -1, so they're
valid, but they aren't.

The minimal solution to the problem is to only populate source_port and
switch_id with what dsa_8021q_rcv() came up with, if the vbid is zero,
i.e. the source port information is trustworthy.

Fixes: c1ae02d87689 ("net: dsa: tag_sja1105: always prefer source port information from INCL_SRCPT")
Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.com>
Reviewed-by: Simon Horman <simon.horman@corigine.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/net/dsa/tag_sja1105.c b/net/dsa/tag_sja1105.c
index 92a626a05e82917dc3fd195a3bb68522d73d239c..db0a6ac6747083b18119c73588d813fb849277de 100644 (file)
--- a/net/dsa/tag_sja1105.c
+++ b/net/dsa/tag_sja1105.c
@@ -573,11 +573,14 @@ static struct sk_buff *sja1105_rcv(struct sk_buff *skb,
                 * if available. This allows us to not overwrite a valid source
                 * port and switch ID with zeroes when receiving link-local
                 * frames from a VLAN-unaware bridged port (non-zero vbid) or a
-                * VLAN-aware bridged port (non-zero vid).
+                * VLAN-aware bridged port (non-zero vid). Furthermore, the
+                * tag_8021q source port information is only of trust when the
+                * vbid is 0 (precise port). Otherwise, tmp_source_port and
+                * tmp_switch_id will be zeroes.
                 */
-               if (source_port == -1)
+               if (vbid == 0 && source_port == -1)
                        source_port = tmp_source_port;
-               if (switch_id == -1)
+               if (vbid == 0 && switch_id == -1)
                        switch_id = tmp_switch_id;
        } else if (source_port == -1 && switch_id == -1) {
                /* Packets with no source information have no chance of