[PATCH 5.15 514/917] net: dsa: avoid refcount warnings when ->port_{fdb,mdb}_del returns error

Greg Kroah-Hartman
2021-11-15T23:42:44Z

From: Vladimir Oltean <vladimir.oltean@nxp.com>

[ Upstream commit 232deb3f9567ce37d99b8616a6c07c1fc0436abf ]

At present, when either of ds->ops->port_fdb_del() or ds->ops->port_mdb_del()
return a non-zero error code, we attempt to save the day and keep the
data structure associated with that switchdev object, as the deletion
procedure did not complete.

However, the way in which we do this is suspicious to the checker in
lib/refcount.c, who thinks it is buggy to increment a refcount that
became zero, and that this is indicative of a use-after-free.

Fixes: 161ca59d39e9 ("net: dsa: reference count the MDB entries at the cross-chip notifier level")
Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
net/dsa/switch.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/net/dsa/switch.c b/net/dsa/switch.c
index 6466d0539af9f..44558fbdc65b3 100644
--- a/net/dsa/switch.c
+++ b/net/dsa/switch.c
@@ -264,7 +264,7 @@ static int dsa_switch_do_mdb_del(struct dsa_switch *ds, int port,

err = ds->ops->port_mdb_del(ds, port, mdb);
if (err) {
- refcount_inc(&a->refcount);
+ refcount_set(&a->refcount, 1);
return err;
}

@@ -329,7 +329,7 @@ static int dsa_switch_do_fdb_del(struct dsa_switch *ds, int port,

err = ds->ops->port_fdb_del(ds, port, addr, vid);
if (err) {
- refcount_inc(&a->refcount);
+ refcount_set(&a->refcount, 1);
return err;
}

--
2.33.0