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Subject[PATCH] bridge: Fix a deadlock when enabling multicast snooping
Date
When enabling multicast snooping, bridge module deadlocks on multicast_lock
if 1) IPv6 is enabled, and 2) there is an existing querier on the same L2
network.

The deadlock was caused by the following sequence: While holding the lock,
br_multicast_open calls br_multicast_join_snoopers, which eventually causes
IP stack to (attempt to) send out a Listener Report (in igmp6_join_group).
Since the destination Ethernet address is a multicast address, br_dev_xmit
feeds the packet back to the bridge via br_multicast_rcv, which in turn
calls br_multicast_add_group, which then deadlocks on multicast_lock.

The fix is to move the call br_multicast_join_snoopers outside of the
critical section. This works since br_multicast_join_snoopers only deals
with IP and does not modify any multicast data structures of the bridge,
so there's no need to hold the lock.

Fixes: 4effd28c1245 ("bridge: join all-snoopers multicast address")

Signed-off-by: Joseph Huang <Joseph.Huang@garmin.com>
---
net/bridge/br_device.c | 3 +++
net/bridge/br_multicast.c | 8 ++++----
net/bridge/br_private.h | 5 +++++
3 files changed, 12 insertions(+), 4 deletions(-)

diff --git a/net/bridge/br_device.c b/net/bridge/br_device.c
index 7730c8f3cb53..8d3ec29d3875 100644
--- a/net/bridge/br_device.c
+++ b/net/bridge/br_device.c
@@ -177,6 +177,9 @@ static int br_dev_open(struct net_device *dev)
br_stp_enable_bridge(br);
br_multicast_open(br);

+ if (br_opt_get(br, BROPT_MULTICAST_ENABLED))
+ br_multicast_join_snoopers(br);
+
return 0;
}

diff --git a/net/bridge/br_multicast.c b/net/bridge/br_multicast.c
index eae898c3cff7..6c8d6b2eed91 100644
--- a/net/bridge/br_multicast.c
+++ b/net/bridge/br_multicast.c
@@ -3286,7 +3286,7 @@ static inline void br_ip6_multicast_join_snoopers(struct net_bridge *br)
}
#endif

-static void br_multicast_join_snoopers(struct net_bridge *br)
+void br_multicast_join_snoopers(struct net_bridge *br)
{
br_ip4_multicast_join_snoopers(br);
br_ip6_multicast_join_snoopers(br);
@@ -3336,9 +3336,6 @@ static void __br_multicast_open(struct net_bridge *br,

void br_multicast_open(struct net_bridge *br)
{
- if (br_opt_get(br, BROPT_MULTICAST_ENABLED))
- br_multicast_join_snoopers(br);
-
__br_multicast_open(br, &br->ip4_own_query);
#if IS_ENABLED(CONFIG_IPV6)
__br_multicast_open(br, &br->ip6_own_query);
@@ -3509,6 +3506,9 @@ int br_multicast_toggle(struct net_bridge *br, unsigned long val)
unlock:
spin_unlock_bh(&br->multicast_lock);

+ if (br_opt_get(br, BROPT_MULTICAST_ENABLED))
+ br_multicast_join_snoopers(br);
+
return 0;
}

diff --git a/net/bridge/br_private.h b/net/bridge/br_private.h
index 345118e35c42..7085dd747130 100644
--- a/net/bridge/br_private.h
+++ b/net/bridge/br_private.h
@@ -792,6 +792,7 @@ void br_multicast_del_port(struct net_bridge_port *port);
void br_multicast_enable_port(struct net_bridge_port *port);
void br_multicast_disable_port(struct net_bridge_port *port);
void br_multicast_init(struct net_bridge *br);
+void br_multicast_join_snoopers(struct net_bridge *br);
void br_multicast_open(struct net_bridge *br);
void br_multicast_stop(struct net_bridge *br);
void br_multicast_dev_del(struct net_bridge *br);
@@ -969,6 +970,10 @@ static inline void br_multicast_init(struct net_bridge *br)
{
}

+static inline void br_multicast_join_snoopers(struct net_bridge *br)
+{
+}
+
static inline void br_multicast_open(struct net_bridge *br)
{
}
--
2.29.2
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