genetlink: fix netns vs. netlink table locking (2)

Similar to commit d136f1bd366fdb7e747ca7e0218171e7a00a98a5,
there's a bug when unregistering a generic netlink family,
which is caught by the might_sleep() added in that commit:

    BUG: sleeping function called from invalid context at net/netlink/af_netlink.c:183
    in_atomic(): 1, irqs_disabled(): 0, pid: 1510, name: rmmod
    2 locks held by rmmod/1510:
     #0:  (genl_mutex){+.+.+.}, at: [<ffffffff8138283b>] genl_unregister_family+0x2b/0x130
     #1:  (rcu_read_lock){.+.+..}, at: [<ffffffff8138270c>] __genl_unregister_mc_group+0x1c/0x120
    Pid: 1510, comm: rmmod Not tainted 2.6.31-wl #444
    Call Trace:
     [<ffffffff81044ff9>] __might_sleep+0x119/0x150
     [<ffffffff81380501>] netlink_table_grab+0x21/0x100
     [<ffffffff813813a3>] netlink_clear_multicast_users+0x23/0x60
     [<ffffffff81382761>] __genl_unregister_mc_group+0x71/0x120
     [<ffffffff81382866>] genl_unregister_family+0x56/0x130
     [<ffffffffa0007d85>] nl80211_exit+0x15/0x20 [cfg80211]
     [<ffffffffa000005a>] cfg80211_exit+0x1a/0x40 [cfg80211]

Fix in the same way by grabbing the netlink table lock
before doing rcu_read_lock().

Signed-off-by: Johannes Berg <johannes@sipsolutions.net>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 3 insertions, 1 deletions

diff --git a/net/netlink/genetlink.c b/net/netlink/genetlink.c
index 566941e03363..44ff3f3810fa 100644
--- a/net/netlink/genetlink.c
+++ b/net/netlink/genetlink.c
@@ -220,10 +220,12 @@ static void __genl_unregister_mc_group(struct genl_family *family,
         struct net *net;
         BUG_ON(grp->family != family);
 
+        netlink_table_grab();
         rcu_read_lock();
         for_each_net_rcu(net)
-                netlink_clear_multicast_users(net->genl_sock, grp->id);
+                __netlink_clear_multicast_users(net->genl_sock, grp->id);
         rcu_read_unlock();
+        netlink_table_ungrab();
 
         clear_bit(grp->id, mc_groups);
         list_del(&grp->list);