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packet: race condition in packet_bind
There is a race conditions between packet_notifier and packet_bind{_spkt}.
It happens if packet_notifier(NETDEV_UNREGISTER) executes between the
time packet_bind{_spkt} takes a reference on the new netdevice and the
time packet_do_bind sets po->ifindex.
In this case the notification can be missed.
If this happens during a dev_change_net_namespace this can result in the
netdevice to be moved to the new namespace while the packet_sock in the
old namespace still holds a reference on it. When the netdevice is later
deleted in the new namespace the deletion hangs since the packet_sock
is not found in the new namespace' &net->packet.sklist.
It can be reproduced with the script below.
This patch makes packet_do_bind check again for the presence of the
netdevice in the packet_sock's namespace after the synchronize_net
in unregister_prot_hook.
More in general it also uses the rcu lock for the duration of the bind
to stop dev_change_net_namespace/rollback_registered_many from
going past the synchronize_net following unlist_netdevice, so that
no NETDEV_UNREGISTER notifications can happen on the new netdevice
while the bind is executing. In order to do this some code from
packet_bind{_spkt} is consolidated into packet_do_dev.
import socket, os, time, sys
proto=7
realDev='em1'
vlanId=400
if len(sys.argv) > 1:
vlanId=int(sys.argv[1])
dev='vlan%d' % vlanId
os.system('taskset -p 0x10 %d' % os.getpid())
s = socket.socket(socket.PF_PACKET, socket.SOCK_RAW, proto)
os.system('ip link add link %s name %s type vlan id %d' %
(realDev, dev, vlanId))
os.system('ip netns add dummy')
pid=os.fork()
if pid == 0:
# dev should be moved while packet_do_bind is in synchronize net
os.system('taskset -p 0x20000 %d' % os.getpid())
os.system('ip link set %s netns dummy' % dev)
os.system('ip netns exec dummy ip link del %s' % dev)
s.close()
sys.exit(0)
time.sleep(.004)
try:
s.bind(('%s' % dev, proto+1))
except:
print 'Could not bind socket'
s.close()
os.system('ip netns del dummy')
sys.exit(0)
os.waitpid(pid, 0)
s.close()
os.system('ip netns del dummy')
sys.exit(0)
Signed-off-by: 
Francesco Ruggeri <fruggeri@arista.com>
Signed-off-by: David S. Miller <davem@davemloft.net>