[PATCH net-next] net: bridge: multicast: fix igmp/mld port context null pointer dereferences

[Nikolay Aleksandrov <razor@blackwall.org>]

From: Nikolay Aleksandrov <nikolay@nvidia.com>

With the recent change to use bridge/port multicast context pointers
instead of bridge/port I missed to convert two locations which pass the
port pointer as-is, but with the new model we need to verify the port
context is non-NULL first and retrieve the port from it. The first
location is when doing querier selection when a query is received, the
second location is when leaving a group. The port context will be null
if the packets originated from the bridge device (i.e. from the host).
The fix is simple just check if the port context exists and retrieve
the port pointer from it.

Fixes: adc47037a7d5 ("net: bridge: multicast: use multicast contexts instead of bridge or port")
Signed-off-by: Nikolay Aleksandrov <nikolay@nvidia.com>
---
note: the != NULL checks are in line with the rest of the code style of
      br_multicast_leave_group()

 net/bridge/br_multicast.c | 14 +++++++++-----
 1 file changed, 9 insertions(+), 5 deletions(-)

diff --git a/net/bridge/br_multicast.c b/net/bridge/br_multicast.c
index 976491951c82..214d1bf854ad 100644
--- a/net/bridge/br_multicast.c
+++ b/net/bridge/br_multicast.c
@@ -2827,9 +2827,11 @@ static int br_ip6_multicast_mld2_report(struct net_bridge_mcast *brmctx,
 #endif
 
 static bool br_ip4_multicast_select_querier(struct net_bridge_mcast *brmctx,
-					    struct net_bridge_port *port,
+					    struct net_bridge_mcast_port *pmctx,
 					    __be32 saddr)
 {
+	struct net_bridge_port *port = pmctx ? pmctx->port : NULL;
+
 	if (!timer_pending(&brmctx->ip4_own_query.timer) &&
 	    !timer_pending(&brmctx->ip4_other_query.timer))
 		goto update;
@@ -2853,9 +2855,11 @@ static bool br_ip4_multicast_select_querier(struct net_bridge_mcast *brmctx,
 
 #if IS_ENABLED(CONFIG_IPV6)
 static bool br_ip6_multicast_select_querier(struct net_bridge_mcast *brmctx,
-					    struct net_bridge_port *port,
+					    struct net_bridge_mcast_port *pmctx,
 					    struct in6_addr *saddr)
 {
+	struct net_bridge_port *port = pmctx ? pmctx->port : NULL;
+
 	if (!timer_pending(&brmctx->ip6_own_query.timer) &&
 	    !timer_pending(&brmctx->ip6_other_query.timer))
 		goto update;
@@ -3076,7 +3080,7 @@ br_ip4_multicast_query_received(struct net_bridge_mcast *brmctx,
 				struct br_ip *saddr,
 				unsigned long max_delay)
 {
-	if (!br_ip4_multicast_select_querier(brmctx, pmctx->port, saddr->src.ip4))
+	if (!br_ip4_multicast_select_querier(brmctx, pmctx, saddr->src.ip4))
 		return;
 
 	br_multicast_update_query_timer(brmctx, query, max_delay);
@@ -3091,7 +3095,7 @@ br_ip6_multicast_query_received(struct net_bridge_mcast *brmctx,
 				struct br_ip *saddr,
 				unsigned long max_delay)
 {
-	if (!br_ip6_multicast_select_querier(brmctx, pmctx->port, &saddr->src.ip6))
+	if (!br_ip6_multicast_select_querier(brmctx, pmctx, &saddr->src.ip6))
 		return;
 
 	br_multicast_update_query_timer(brmctx, query, max_delay);
@@ -3322,7 +3326,7 @@ br_multicast_leave_group(struct net_bridge_mcast *brmctx,
 		mod_timer(&own_query->timer, time);
 
 		for (p = mlock_dereference(mp->ports, brmctx->br);
-		     p != NULL;
+		     p != NULL && pmctx != NULL;
 		     p = mlock_dereference(p->next, brmctx->br)) {
 			if (!br_port_group_equal(p, pmctx->port, src))
 				continue;
-- 
2.31.1