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bridge: Fix a deadlock when enabling multicast snooping 

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: 4effd28c12 ("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>
This commit is contained in:
Joseph Huang 2020-12-04 18:56:28 -05:00 committed by Jakub Kicinski
parent eb96b686fc
commit 851d0a73c9
3 changed files with 41 additions and 9 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

6
net/bridge/br_device.c
View File

@ -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;

34
net/bridge/br_multicast.c
View File

@ -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 +3481,7 @@ 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 change_snoopers = false;
spin_lock_bh(&br->multicast_lock);
if (!!br_opt_get(br, BROPT_MULTICAST_ENABLED) == !!val)
@ -3495,7 +3490,7 @@ 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);
change_snoopers = true;
goto unlock;
}
@ -3506,9 +3501,30 @@ 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_opt_get(br, BROPT_MULTICAST_ENABLED))
br_multicast_join_snoopers(br);
else
br_multicast_leave_snoopers(br);
}
return 0;
}

10
net/bridge/br_private.h
View File

@ -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)
{
}