gluon/patches/openwrt/0022-kernel-bridge-Fix-a-deadlock-when-enabling-multicast-snooping.patch

From: Linus Lüssing <linus.luessing@c0d3.blue>
Date: Mon, 25 Jan 2021 01:38:19 +0100
Subject: kernel: bridge: Fix a deadlock when enabling multicast snooping

[ Upstream commit 851d0a73c90e6c8c63fef106c6c1e73df7e05d9d ]

From: Joseph Huang <Joseph.Huang@garmin.com>

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@garmin.com>
Acked-by: Nikolay Aleksandrov <nikolay@nvidia.com>
Link: https://lore.kernel.org/r/20201204235628.50653-1-Joseph.Huang@garmin.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
[linus.luessing@c0d3.blue: backported to 4.4]

diff --git a/target/linux/generic/backport-4.14/120-bridge-Fix-a-deadlock-when-enabling-multicast-snoopi.patch b/target/linux/generic/backport-4.14/120-bridge-Fix-a-deadlock-when-enabling-multicast-snoopi.patch
new file mode 100644
index 0000000000000000000000000000000000000000..e89d9e3eb2063b1f478c0217aaa3c89d14880043
--- /dev/null
+++ b/target/linux/generic/backport-4.14/120-bridge-Fix-a-deadlock-when-enabling-multicast-snoopi.patch
@@ -0,0 +1,209 @@
+From 0e125bd346d3b9d6997e525b263834f6b650cf60 Mon Sep 17 00:00:00 2001
+From: Joseph Huang <Joseph.Huang@garmin.com>
+Date: Fri, 4 Dec 2020 18:56:28 -0500
+Subject: [PATCH] bridge: Fix a deadlock when enabling multicast snooping
+
+[ Upstream commit 851d0a73c90e6c8c63fef106c6c1e73df7e05d9d ]
+
+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@garmin.com>
+Acked-by: Nikolay Aleksandrov <nikolay@nvidia.com>
+Link: https://lore.kernel.org/r/20201204235628.50653-1-Joseph.Huang@garmin.com
+Signed-off-by: Jakub Kicinski <kuba@kernel.org>
+Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
+[linus.luessing@c0d3.blue: backported to 4.4]
+---
+ net/bridge/br_device.c    |  6 ++++++
+ net/bridge/br_multicast.c | 34 +++++++++++++++++++++++++---------
+ net/bridge/br_private.h   | 10 ++++++++++
+ 3 files changed, 41 insertions(+), 9 deletions(-)
+
+diff --git a/net/bridge/br_device.c b/net/bridge/br_device.c
+index b7cc322acdc8..4bd8a7ba002a 100644
+--- a/net/bridge/br_device.c
++++ b/net/bridge/br_device.c
+@@ -140,6 +140,9 @@ static int br_dev_open(struct net_device *dev)
+ 	br_stp_enable_bridge(br);
+ 	br_multicast_open(br);
+ 
++	if (!br->multicast_disabled)
++		br_multicast_join_snoopers(br);
++
+ 	return 0;
+ }
+ 
+@@ -160,6 +163,9 @@ static int br_dev_stop(struct net_device *dev)
+ 	br_stp_disable_bridge(br);
+ 	br_multicast_stop(br);
+ 
++	if (!br->multicast_disabled)
++		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 6d8d1cf2ddc6..1b1d06549583 100644
+--- a/net/bridge/br_multicast.c
++++ b/net/bridge/br_multicast.c
+@@ -2314,7 +2314,7 @@ 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);
+@@ -2345,7 +2345,7 @@ 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);
+@@ -2364,9 +2364,6 @@ static void __br_multicast_open(struct net_bridge *br,
+ 
+ void br_multicast_open(struct net_bridge *br)
+ {
+-	if (!br->multicast_disabled)
+-		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);
+@@ -2382,9 +2379,6 @@ 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->multicast_disabled)
+-		br_multicast_leave_snoopers(br);
+ }
+ 
+ void br_multicast_dev_del(struct net_bridge *br)
+@@ -2540,6 +2534,7 @@ int br_multicast_toggle(struct net_bridge *br, unsigned long val)
+ {
+ 	struct net_bridge_mdb_htable *mdb;
+ 	struct net_bridge_port *port;
++	bool change_snoopers = false;
+ 	int err = 0;
+ 
+ 	spin_lock_bh(&br->multicast_lock);
+@@ -2549,7 +2544,7 @@ int br_multicast_toggle(struct net_bridge *br, unsigned long val)
+ 	br_mc_disabled_update(br->dev, !val);
+ 	br->multicast_disabled = !val;
+ 	if (br->multicast_disabled) {
+-		br_multicast_leave_snoopers(br);
++		change_snoopers = true;
+ 		goto unlock;
+ 	}
+ 
+@@ -2575,9 +2570,30 @@ 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);
+ 
++	change_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 (change_snoopers) {
++		if (!br->multicast_disabled)
++			br_multicast_join_snoopers(br);
++		else
++			br_multicast_leave_snoopers(br);
++	}
++
+ 	return err;
+ }
+ 
+diff --git a/net/bridge/br_private.h b/net/bridge/br_private.h
+index bbf7513c1d16..cb701c31199d 100644
+--- a/net/bridge/br_private.h
++++ b/net/bridge/br_private.h
+@@ -611,6 +611,8 @@ 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);
+@@ -736,6 +738,14 @@ 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
+