path: root/net/netlink/genetlink.c
diff options
authorJohannes Berg <>2015-01-16 11:37:14 +0100
committerDavid S. Miller <>2015-01-16 17:04:25 -0500
commitee1c244219fd652964710a6cc3e4f922e86aa492 (patch)
tree4420f067c6b1bbec48aa33a6ab96c627e2c2dbde /net/netlink/genetlink.c
parent5ad6300524c0332ac67e912c20d6e5cf262ba58f (diff)
genetlink: synchronize socket closing and family removal
In addition to the problem Jeff Layton reported, I looked at the code and reproduced the same warning by subscribing and removing the genl family with a socket still open. This is a fairly tricky race which originates in the fact that generic netlink allows the family to go away while sockets are still open - unlike regular netlink which has a module refcount for every open socket so in general this cannot be triggered. Trying to resolve this issue by the obvious locking isn't possible as it will result in deadlocks between unregistration and group unbind notification (which incidentally lockdep doesn't find due to the home grown locking in the netlink table.) To really resolve this, introduce a "closing socket" reference counter (for generic netlink only, as it's the only affected family) in the core netlink code and use that in generic netlink to wait for all the sockets that are being closed at the same time as a generic netlink family is removed. This fixes the race that when a socket is closed, it will should call the unbind, but if the family is removed at the same time the unbind will not find it, leading to the warning. The real problem though is that in this case the unbind could actually find a new family that is registered to have a multicast group with the same ID, and call its mcast_unbind() leading to confusing. Also remove the warning since it would still trigger, but is now no longer a problem. This also moves the code in af_netlink.c to before unreferencing the module to avoid having the same problem in the normal non-genl case. Signed-off-by: Johannes Berg <> Signed-off-by: David S. Miller <>
Diffstat (limited to 'net/netlink/genetlink.c')
1 files changed, 9 insertions, 7 deletions
diff --git a/net/netlink/genetlink.c b/net/netlink/genetlink.c
index c18d3f5624b2..ee57459fc258 100644
--- a/net/netlink/genetlink.c
+++ b/net/netlink/genetlink.c
@@ -23,6 +23,9 @@
static DEFINE_MUTEX(genl_mutex); /* serialization of message processing */
static DECLARE_RWSEM(cb_lock);
+atomic_t genl_sk_destructing_cnt = ATOMIC_INIT(0);
void genl_lock(void)
@@ -435,15 +438,18 @@ int genl_unregister_family(struct genl_family *family)
- genl_unregister_mc_groups(family);
list_for_each_entry(rc, genl_family_chain(family->id), family_list) {
if (family->id != rc->id || strcmp(rc->name, family->name))
+ genl_unregister_mc_groups(family);
family->n_ops = 0;
- genl_unlock_all();
+ up_write(&cb_lock);
+ wait_event(genl_sk_destructing_waitq,
+ atomic_read(&genl_sk_destructing_cnt) == 0);
+ genl_unlock();
genl_ctrl_event(CTRL_CMD_DELFAMILY, family, NULL, 0);
@@ -1014,7 +1020,6 @@ static int genl_bind(struct net *net, int group)
static void genl_unbind(struct net *net, int group)
int i;
- bool found = false;
for (i = 0; i < GENL_FAM_TAB_SIZE; i++) {
@@ -1027,14 +1032,11 @@ static void genl_unbind(struct net *net, int group)
if (f->mcast_unbind)
f->mcast_unbind(net, fam_grp);
- found = true;
- WARN_ON(!found);
static int __net_init genl_pernet_init(struct net *net)