From ab102b80cef28c20b3ef7794806c3a982c6444fc Mon Sep 17 00:00:00 2001 From: WANG Cong Date: Tue, 11 Oct 2016 10:56:45 -0700 Subject: [PATCH] net_sched: reorder pernet ops and act ops registrations Krister reported a kernel NULL pointer dereference after tcf_action_init_1() invokes a_o->init(), it is a race condition where one thread calling tcf_register_action() to initialize the netns data after putting act ops in the global list and the other thread searching the list and then calling a_o->init(net, ...). Fix this by moving the pernet ops registration before making the action ops visible. This is fine because: a) we don't rely on act_base in pernet ops->init(), b) in the worst case we have a fully initialized netns but ops is still not ready so new actions still can't be created. Reported-by: Krister Johansen Tested-by: Krister Johansen Cc: Jamal Hadi Salim Signed-off-by: Cong Wang Acked-by: Jamal Hadi Salim Signed-off-by: David S. Miller --- net/sched/act_api.c | 19 +++++++++++-------- 1 file changed, 11 insertions(+), 8 deletions(-) diff --git a/net/sched/act_api.c b/net/sched/act_api.c index c9102172ce3b..a512b18c0088 100644 --- a/net/sched/act_api.c +++ b/net/sched/act_api.c @@ -341,22 +341,25 @@ int tcf_register_action(struct tc_action_ops *act, if (!act->act || !act->dump || !act->init || !act->walk || !act->lookup) return -EINVAL; + /* We have to register pernet ops before making the action ops visible, + * otherwise tcf_action_init_1() could get a partially initialized + * netns. + */ + ret = register_pernet_subsys(ops); + if (ret) + return ret; + write_lock(&act_mod_lock); list_for_each_entry(a, &act_base, head) { if (act->type == a->type || (strcmp(act->kind, a->kind) == 0)) { write_unlock(&act_mod_lock); + unregister_pernet_subsys(ops); return -EEXIST; } } list_add_tail(&act->head, &act_base); write_unlock(&act_mod_lock); - ret = register_pernet_subsys(ops); - if (ret) { - tcf_unregister_action(act, ops); - return ret; - } - return 0; } EXPORT_SYMBOL(tcf_register_action); @@ -367,8 +370,6 @@ int tcf_unregister_action(struct tc_action_ops *act, struct tc_action_ops *a; int err = -ENOENT; - unregister_pernet_subsys(ops); - write_lock(&act_mod_lock); list_for_each_entry(a, &act_base, head) { if (a == act) { @@ -378,6 +379,8 @@ int tcf_unregister_action(struct tc_action_ops *act, } } write_unlock(&act_mod_lock); + if (!err) + unregister_pernet_subsys(ops); return err; } EXPORT_SYMBOL(tcf_unregister_action);