On 05/12/2020 01:56, Joseph Huang wrote:
> 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 | 34 +++++++++++++++++++++++++---------
> net/bridge/br_private.h | 10 ++++++++++
> 3 files changed, 41 insertions(+), 9 deletions(-)
>
LGTM, thanks!
Acked-by: Nikolay Aleksandrov <nikolay@xxxxxxxxxx>
