[PATCH net-next v2 06/18] net: dsa: mv88e6xxx: refactor mv88e6xxx_port_vlan()

[Jakob Koschel]

To avoid bugs and speculative execution exploits due to type-confused
pointers at the end of a list_for_each_entry() loop, one measure is to
restrict code to not use the iterator variable outside the loop block.

In the case of mv88e6xxx_port_vlan(), this isn't a problem, as we never
let the loops exit through "natural causes" anyway, by using a "found"
variable and then using the last "dp" iterator prior to the break, which
is a safe thing to do.

Nonetheless, with the expected new syntax, this pattern will no longer
be possible.

Profit off of the occasion and break the two port finding methods into
smaller sub-functions. Somehow, returning a copy of the iterator pointer
is still accepted.

This change makes it redundant to have a "bool found", since the "dp"
from mv88e6xxx_port_vlan() now holds NULL if we haven't found what we
were looking for.

Signed-off-by: Jakob Koschel <jakobkoschel@xxxxxxxxx>
Signed-off-by: Vladimir Oltean <vladimir.oltean@xxxxxxx>
---
 drivers/net/dsa/mv88e6xxx/chip.c | 54 ++++++++++++++++++--------------
 1 file changed, 31 insertions(+), 23 deletions(-)

diff --git a/drivers/net/dsa/mv88e6xxx/chip.c b/drivers/net/dsa/mv88e6xxx/chip.c
index b3aa0e5bc842..1f35e89053e6 100644
--- a/drivers/net/dsa/mv88e6xxx/chip.c
+++ b/drivers/net/dsa/mv88e6xxx/chip.c
@@ -1378,42 +1378,50 @@ static int mv88e6xxx_set_mac_eee(struct dsa_switch *ds, int port,
 	return 0;
 }
 
+static struct dsa_port *mv88e6xxx_find_port(struct dsa_switch_tree *dst,
+					    int sw_index, int port)
+{
+	struct dsa_port *dp;
+
+	list_for_each_entry(dp, &dst->ports, list)
+		if (dp->ds->index == sw_index && dp->index == port)
+			return dp;
+
+	return NULL;
+}
+
+static struct dsa_port *
+mv88e6xxx_find_port_by_bridge_num(struct dsa_switch_tree *dst,
+				  unsigned int bridge_num)
+{
+	struct dsa_port *dp;
+
+	list_for_each_entry(dp, &dst->ports, list)
+		if (dsa_port_bridge_num_get(dp) == bridge_num)
+			return dp;
+
+	return NULL;
+}
+
 /* Mask of the local ports allowed to receive frames from a given fabric port */
 static u16 mv88e6xxx_port_vlan(struct mv88e6xxx_chip *chip, int dev, int port)
 {
 	struct dsa_switch *ds = chip->ds;
 	struct dsa_switch_tree *dst = ds->dst;
 	struct dsa_port *dp, *other_dp;
-	bool found = false;
 	u16 pvlan;
 
-	/* dev is a physical switch */
 	if (dev <= dst->last_switch) {
-		list_for_each_entry(dp, &dst->ports, list) {
-			if (dp->ds->index == dev && dp->index == port) {
-				/* dp might be a DSA link or a user port, so it
-				 * might or might not have a bridge.
-				 * Use the "found" variable for both cases.
-				 */
-				found = true;
-				break;
-			}
-		}
-	/* dev is a virtual bridge */
+		/* dev is a physical switch */
+		dp = mv88e6xxx_find_port(dst, dev, port);
 	} else {
-		list_for_each_entry(dp, &dst->ports, list) {
-			unsigned int bridge_num = dsa_port_bridge_num_get(dp);
-
-			if (bridge_num + dst->last_switch != dev)
-				continue;
-
-			found = true;
-			break;
-		}
+		/* dev is a virtual bridge */
+		dp = mv88e6xxx_find_port_by_bridge_num(dst,
+						       dev - dst->last_switch);
 	}
 
 	/* Prevent frames from unknown switch or virtual bridge */
-	if (!found)
+	if (!dp)
 		return 0;
 
 	/* Frames from DSA links and CPU ports can egress any local port */
-- 
2.25.1