From: Linus Lüssing 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 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 Acked-by: Nikolay Aleksandrov Link: https://lore.kernel.org/r/20201204235628.50653-1-Joseph.Huang@garmin.com Signed-off-by: Jakub Kicinski Signed-off-by: Greg Kroah-Hartman [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 +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 +Acked-by: Nikolay Aleksandrov +Link: https://lore.kernel.org/r/20201204235628.50653-1-Joseph.Huang@garmin.com +Signed-off-by: Jakub Kicinski +Signed-off-by: Greg Kroah-Hartman +[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 +