net: fix deadlock while clearing neighbor proxy table

commit 53b76cdf7e8fecec1d09e38aad2f8579882591a8 upstream.

When coming from ndisc_netdev_event() in net/ipv6/ndisc.c,
neigh_ifdown() is called with &nd_tbl, locking this while
clearing the proxy neighbor entries when eg. deleting an
interface. Calling the table's pndisc_destructor() with the
lock still held, however, can cause a deadlock: When a
multicast listener is available an IGMP packet of type
ICMPV6_MGM_REDUCTION may be sent out. When reaching
ip6_finish_output2(), if no neighbor entry for the target
address is found, __neigh_create() is called with &nd_tbl,
which it'll want to lock.

Move the elements into their own list, then unlock the table
and perform the destruction.

Change-Id: I3e0bb9f41948210b1419fa35b3537d2a14afdd18
Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=199289
Fixes: 6fd6ce2056de ("ipv6: Do not depend on rt->n in ip6_finish_output2().")
Signed-off-by: Wolfgang Bumiller <w.bumiller@proxmox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
[bwh: Backported to 3.16:
 - Move the (useless) call to release_net() as well
 - Adjust context]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>

0 files changed, 0 insertions, 0 deletions