[PATCH net] net: bridge: allow users setting EXT_LEARN for user FDB entries

[Jonas Gorski]

When userspace wants to take over a fdb entry by setting it as
EXTERN_LEARNED, we set both flags BR_FDB_ADDED_BY_EXT_LEARN and
BR_FDB_ADDED_BY_USER in br_fdb_external_learn_add().

If the bridge updates the entry later because its port changed, we clear
the BR_FDB_ADDED_BY_EXT_LEARN flag, but leave the BR_FDB_ADDED_BY_USER
flag set.

If userspace then wants to take over the entry again,
br_fdb_external_learn_add() sees that BR_FDB_ADDED_BY_USER and skips
setting the BR_FDB_ADDED_BY_EXT_LEARN flags, thus silently ignores the
update:

   if (test_bit(BR_FDB_ADDED_BY_EXT_LEARN, &fdb->flags)) {
           /* Refresh entry */
           fdb->used = jiffies;
   } else if (!test_bit(BR_FDB_ADDED_BY_USER, &fdb->flags)) {
           /* Take over SW learned entry */
           set_bit(BR_FDB_ADDED_BY_EXT_LEARN, &fdb->flags);
           modified = true;
   }

Fix this by relaxing the condition for setting BR_FDB_ADDED_BY_EXT_LEARN
by also allowing it if swdev_notify is true, which it will only be for
user initiated updates.

Fixes: 710ae7287737 ("net: bridge: Mark FDB entries that were added by user as such")
Signed-off-by: Jonas Gorski <jonas.gorski@xxxxxxxx>
---
 net/bridge/br_fdb.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/net/bridge/br_fdb.c b/net/bridge/br_fdb.c
index c77591e63841..c5d9ae13a6fb 100644
--- a/net/bridge/br_fdb.c
+++ b/net/bridge/br_fdb.c
@@ -1472,7 +1472,8 @@ int br_fdb_external_learn_add(struct net_bridge *br, struct net_bridge_port *p,
 		if (test_bit(BR_FDB_ADDED_BY_EXT_LEARN, &fdb->flags)) {
 			/* Refresh entry */
 			fdb->used = jiffies;
-		} else if (!test_bit(BR_FDB_ADDED_BY_USER, &fdb->flags)) {
+		} else if (swdev_notify ||
+			   !test_bit(BR_FDB_ADDED_BY_USER, &fdb->flags)) {
 			/* Take over SW learned entry */
 			set_bit(BR_FDB_ADDED_BY_EXT_LEARN, &fdb->flags);
 			modified = true;
-- 
2.46.0


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