[PATCH v2] bridge: Fix a deadlock when enabling multicast snooping
From: Joseph Huang
Date: Fri Dec 04 2020 - 16:40:39 EST
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.
Steps to reproduce:
1. sysctl net.ipv6.conf.all.force_mld_version=1
2. have another querier
3. ip link set dev bridge type bridge mcast_snooping 0 && \
ip link set dev bridge type bridge mcast_snooping 1 < deadlock >
A typical call trace looks like the following:
[ 936.251495] _raw_spin_lock+0x5c/0x68
[ 936.255221] br_multicast_add_group+0x40/0x170 [bridge]
[ 936.260491] br_multicast_rcv+0x7ac/0xe30 [bridge]
[ 936.265322] br_dev_xmit+0x140/0x368 [bridge]
[ 936.269689] dev_hard_start_xmit+0x94/0x158
[ 936.273876] __dev_queue_xmit+0x5ac/0x7f8
[ 936.277890] dev_queue_xmit+0x10/0x18
[ 936.281563] neigh_resolve_output+0xec/0x198
[ 936.285845] ip6_finish_output2+0x240/0x710
[ 936.290039] __ip6_finish_output+0x130/0x170
[ 936.294318] ip6_output+0x6c/0x1c8
[ 936.297731] NF_HOOK.constprop.0+0xd8/0xe8
[ 936.301834] igmp6_send+0x358/0x558
[ 936.305326] igmp6_join_group.part.0+0x30/0xf0
[ 936.309774] igmp6_group_added+0xfc/0x110
[ 936.313787] __ipv6_dev_mc_inc+0x1a4/0x290
[ 936.317885] ipv6_dev_mc_inc+0x10/0x18
[ 936.321677] br_multicast_open+0xbc/0x110 [bridge]
[ 936.326506] br_multicast_toggle+0xec/0x140 [bridge]
Fixes: 4effd28c1245 ("bridge: join all-snoopers multicast address")
Signed-off-by: Joseph Huang <Joseph.Huang@xxxxxxxxxx>
---
net/bridge/br_device.c | 6 ++++++
net/bridge/br_multicast.c | 33 ++++++++++++++++++++++++---------
net/bridge/br_private.h | 10 ++++++++++
3 files changed, 40 insertions(+), 9 deletions(-)
diff --git a/net/bridge/br_device.c b/net/bridge/br_device.c
index 7730c8f3cb53..d3ea9d0779fb 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;
}
@@ -197,6 +200,9 @@ static int br_dev_stop(struct net_device *dev)
br_stp_disable_bridge(br);
br_multicast_stop(br);
+ if (br_opt_get(br, BROPT_MULTICAST_ENABLED))
+ br_multicast_leave_snoopers(br);
+
netif_stop_queue(dev);
return 0;
diff --git a/net/bridge/br_multicast.c b/net/bridge/br_multicast.c
index eae898c3cff7..426fe00db708 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);
@@ -3317,7 +3317,7 @@ static inline void br_ip6_multicast_leave_snoopers(struct net_bridge *br)
}
#endif
-static void br_multicast_leave_snoopers(struct net_bridge *br)
+void br_multicast_leave_snoopers(struct net_bridge *br)
{
br_ip4_multicast_leave_snoopers(br);
br_ip6_multicast_leave_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);
@@ -3354,9 +3351,6 @@ void br_multicast_stop(struct net_bridge *br)
del_timer_sync(&br->ip6_other_query.timer);
del_timer_sync(&br->ip6_own_query.timer);
#endif
-
- if (br_opt_get(br, BROPT_MULTICAST_ENABLED))
- br_multicast_leave_snoopers(br);
}
void br_multicast_dev_del(struct net_bridge *br)
@@ -3487,6 +3481,8 @@ static void br_multicast_start_querier(struct net_bridge *br,
int br_multicast_toggle(struct net_bridge *br, unsigned long val)
{
struct net_bridge_port *port;
+ bool join_snoopers = false;
+ bool leave_snoopers = false;
spin_lock_bh(&br->multicast_lock);
if (!!br_opt_get(br, BROPT_MULTICAST_ENABLED) == !!val)
@@ -3495,7 +3491,7 @@ int br_multicast_toggle(struct net_bridge *br, unsigned long val)
br_mc_disabled_update(br->dev, val);
br_opt_toggle(br, BROPT_MULTICAST_ENABLED, !!val);
if (!br_opt_get(br, BROPT_MULTICAST_ENABLED)) {
- br_multicast_leave_snoopers(br);
+ leave_snoopers = true;
goto unlock;
}
@@ -3506,9 +3502,28 @@ int br_multicast_toggle(struct net_bridge *br, unsigned long val)
list_for_each_entry(port, &br->port_list, list)
__br_multicast_enable_port(port);
+ join_snoopers = true;
+
unlock:
spin_unlock_bh(&br->multicast_lock);
+ /* br_multicast_join_snoopers has the potential to cause
+ * an MLD Report/Leave to be delivered to br_multicast_rcv,
+ * which would in turn call br_multicast_add_group, which would
+ * attempt to acquire multicast_lock. This function should be
+ * called after the lock has been released to avoid deadlocks on
+ * multicast_lock.
+ *
+ * br_multicast_leave_snoopers does not have the problem since
+ * br_multicast_rcv first checks BROPT_MULTICAST_ENABLED, and
+ * returns without calling br_multicast_ipv4/6_rcv if it's not
+ * enabled. Moved both functions out just for symmetry.
+ */
+ if (join_snoopers)
+ br_multicast_join_snoopers(br);
+ else if (leave_snoopers)
+ br_multicast_leave_snoopers(br);
+
return 0;
}
diff --git a/net/bridge/br_private.h b/net/bridge/br_private.h
index 345118e35c42..8424464186a6 100644
--- a/net/bridge/br_private.h
+++ b/net/bridge/br_private.h
@@ -792,6 +792,8 @@ 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_leave_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 +971,14 @@ 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_leave_snoopers(struct net_bridge *br)
+{
+}
+
static inline void br_multicast_open(struct net_bridge *br)
{
}
--
2.29.2