netlink: fix wrong subscription bitmask to group mapping in

netlink: fix wrong subscription bitmask to group mapping in

The subscription bitmask passed via struct sockaddr_nl is converted to
the group number when calling the netlink_bind() and netlink_unbind()
callbacks.

The conversion is however incorrect since bitmask (1 << 0) needs to be
mapped to group number 1. Note that you cannot specify the group number 0
(usually known as _NONE) from setsockopt() using NETLINK_ADD_MEMBERSHIP
since this is rejected through -EINVAL.

This problem became noticeable since 97840cb ("netfilter: nfnetlink:
fix insufficient validation in nfnetlink_bind") when binding to bitmask
(1 << 0) in ctnetlink.

Reported-by: Andre Tomt <[email protected]>
Reported-by: Ivan Delalande <[email protected]>
Signed-off-by: Pablo Neira Ayuso <[email protected]>
Signed-off-by: David S. Miller <[email protected]>