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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 <kjlx@templeofstupid.com>
Tested-by: Krister Johansen <kjlx@templeofstupid.com>
Cc: Jamal Hadi Salim <jhs@mojatatu.com>
Signed-off-by: Cong Wang <xiyou.wangcong@gmail.com>
Acked-by: Jamal Hadi Salim <jhs@mojatatu.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
WANG Cong 2016-10-11 10:56:45 -07:00 committed by David S. Miller
parent d1ef006dc1
commit ab102b80ce
1 changed files with 11 additions and 8 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

19
net/sched/act_api.c
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@ -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);