Re: [PATCH v5 net-next 01/15] net: bridge: mst: Multiple Spanning Tree (MST) mode

On Mon, Jan 09, 2023 at 01:56:53PM +0200, Vladimir Oltean wrote:

On Mon, Jan 09, 2023 at 01:43:46PM +0200, Ido Schimmel wrote:

quoted

OK, thanks for confirming. Will send a patch later this week if Tobias
won't take care of it by then. First patch will probably be [1] to make
sure we dump the correct MST state to user space. It will also make it
easier to show the problem and validate the fix.

[1]

diff --git a/net/bridge/br.c b/net/bridge/br.c
index 4f5098d33a46..f02a1ad589de 100644
--- a/net/bridge/br.c
+++ b/net/bridge/br.c

@@ -286,7 +286,7 @@ int br_boolopt_get(const struct net_bridge *br, enum br_boolopt_id opt)
 	case BR_BOOLOPT_MCAST_VLAN_SNOOPING:
 		return br_opt_get(br, BROPT_MCAST_VLAN_SNOOPING_ENABLED);
 	case BR_BOOLOPT_MST_ENABLE:
-		return br_opt_get(br, BROPT_MST_ENABLED);
+		return br_mst_is_enabled(br);

Well, this did report the correct MST state despite the incorrect static
branch state, no? The users of br_mst_is_enabled(br) are broken, not
those of br_opt_get(br, BROPT_MST_ENABLED).

I should have said "actual"/"effective" instead of "correct". IMO, it's
better to use the same conditional in the both the data and control
paths to eliminate discrepancies. Without the patch, a user will see
that MST is supposedly enabled when it is actually disabled in the data
path.

Anyway, I see there's a br_mst_is_enabled() and also a br_mst_enabled()?!
One is used in the fast path and the other in the slow path. They should
probably be merged, I guess. They both exist probably because somebody
thought that the "if (!netif_is_bridge_master(dev))" test is redundant
in the fast path.

The single user of br_mst_enabled() (DSA) is not affected by the bug
(only the SW data path is), so I suggest making this consolidation in
net-next after the bug is fixed. OK?

quoted

 	default:
 		/* shouldn't be called with unsupported options */
 		WARN_ON(1);

diff --git a/net/bridge/br_private.h b/net/bridge/br_private.h
index 75aff9bbf17e..7f0475f62d45 100644
--- a/net/bridge/br_private.h
+++ b/net/bridge/br_private.h

@@ -1827,7 +1827,7 @@ static inline bool br_vlan_state_allowed(u8 state, bool learn_allow)
 /* br_mst.c */
 #ifdef CONFIG_BRIDGE_VLAN_FILTERING
 DECLARE_STATIC_KEY_FALSE(br_mst_used);
-static inline bool br_mst_is_enabled(struct net_bridge *br)
+static inline bool br_mst_is_enabled(const struct net_bridge *br)
 {
 	return static_branch_unlikely(&br_mst_used) &&
 		br_opt_get(br, BROPT_MST_ENABLED);

@@ -1845,7 +1845,7 @@ int br_mst_fill_info(struct sk_buff *skb,
 int br_mst_process(struct net_bridge_port *p, const struct nlattr *mst_attr,
 		   struct netlink_ext_ack *extack);
 #else
-static inline bool br_mst_is_enabled(struct net_bridge *br)
+static inline bool br_mst_is_enabled(const struct net_bridge *br)
 {
 	return false;
 }