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SubjectRe: [PATCH net 2/2] net: dsa: Avoid cross-chip syncing of VLAN filtering
On Mon, Jan 24, 2022 at 10:09:44PM +0100, Tobias Waldekranz wrote:
> Changes to VLAN filtering are not applicable to cross-chip
> notifications.

Yes, it seems so. In a cross-chip setup, ports will individually leave
the bridge, leaving every switch a chance to unset VLAN filtering.
We have this check in dsa_port_vlan_filtering(), so it's easy to forget
that the function is called more times than actually needed:

if (dsa_port_is_vlan_filtering(dp) == vlan_filtering)
return 0;

Sorry.

> On a system like this:
>
> .-----. .-----. .-----.
> | sw1 +---+ sw2 +---+ sw3 |
> '-1-2-' '-1-2-' '-1-2-'
>
> Before this change, upon sw1p1 leaving a bridge, a call to
> dsa_port_vlan_filtering would also be made to sw2p1 and sw3p1.
>
> In this scenario:
>
> .---------. .-----. .-----.
> | sw1 +---+ sw2 +---+ sw3 |
> '-1-2-3-4-' '-1-2-' '-1-2-'
>
> When sw1p4 would leave a bridge, dsa_port_vlan_filtering would be
> called for sw2 and sw3 with a non-existing port - leading to array
> out-of-bounds accesses and crashes on mv88e6xxx.
>
> Fixes: d371b7c92d19 ("net: dsa: Unset vlan_filtering when ports leave the bridge")
> Signed-off-by: Tobias Waldekranz <tobias@waldekranz.com>
> ---
> net/dsa/switch.c | 8 +++++---
> 1 file changed, 5 insertions(+), 3 deletions(-)
>
> diff --git a/net/dsa/switch.c b/net/dsa/switch.c
> index 9f9b70d6070a..517cc83d13cc 100644
> --- a/net/dsa/switch.c
> +++ b/net/dsa/switch.c
> @@ -180,9 +180,11 @@ static int dsa_switch_bridge_leave(struct dsa_switch *ds,
> info->sw_index, info->port,
> info->bridge);
>
> - err = dsa_switch_sync_vlan_filtering(ds, info);
> - if (err)
> - return err;
> + if (ds->dst->index == info->tree_index && ds->index == info->sw_index) {
> + err = dsa_switch_sync_vlan_filtering(ds, info);
> + if (err)
> + return err;
> + }

As net-next material, we could probably move this call to
dsa_port_switchdev_unsync_attrs() where there's even a comment that
references it, and do away with the targeted switch check.

>
> return dsa_tag_8021q_bridge_leave(ds, info);
> }
> --
> 2.25.1
>

Reviewed-by: Vladimir Oltean <olteanv@gmail.com>

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