Re: [PATCH net] net: dsa: tag_sja1105: fix source port decoding in vlan_filtering=0 bridge mode

[Simon Horman]

On Sat, Jul 01, 2023 at 01:20:10AM +0300, Vladimir Oltean wrote:
> 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@xxxxxxx>

Reviewed-by: Simon Horman <simon.horman@xxxxxxxxxxxx>