[PATCH v2 net] net: dsa: Discard frames from unused ports

[Andrew Lunn <andrew@lunn.ch>]

The Marvell switches under some conditions will pass a frame to the
host with the port being the CPU port. Such frames are invalid, and
should be dropped. Not dropping them can result in a crash when
incrementing the receive statistics for an invalid port.

Reported-by: Chris Healy <cphealy@gmail.com>
Fixes: 91da11f870f0 ("net: Distributed Switch Architecture protocol support")
Signed-off-by: Andrew Lunn <andrew@lunn.ch>
---
v2:
Use an earlier revision for the fixes tag.
Add unlikely annotation
---
 net/dsa/dsa_priv.h | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/net/dsa/dsa_priv.h b/net/dsa/dsa_priv.h
index 70de7895e5b8..053731473c99 100644
--- a/net/dsa/dsa_priv.h
+++ b/net/dsa/dsa_priv.h
@@ -126,6 +126,7 @@ static inline struct net_device *dsa_master_find_slave(struct net_device *dev,
 	struct dsa_port *cpu_dp = dev->dsa_ptr;
 	struct dsa_switch_tree *dst = cpu_dp->dst;
 	struct dsa_switch *ds;
+	struct dsa_port *slave_port;
 
 	if (device < 0 || device >= DSA_MAX_SWITCHES)
 		return NULL;
@@ -137,7 +138,12 @@ static inline struct net_device *dsa_master_find_slave(struct net_device *dev,
 	if (port < 0 || port >= ds->num_ports)
 		return NULL;
 
-	return ds->ports[port].slave;
+	slave_port = &ds->ports[port];
+
+	if (unlikely(slave_port->type != DSA_PORT_TYPE_USER))
+		return NULL;
+
+	return slave_port->slave;
 }
 
 /* port.c */
-- 
2.16.3