On 9/21/19 7:08 PM, Jakub Kicinski wrote:
> On Wed, 18 Sep 2019 14:37:21 -0700, Cong Wang wrote:
>> On Wed, Sep 18, 2019 at 12:57 PM 'Eric Dumazet' via syzkaller
>> <syzkal...@googlegroups.com> wrote:
>>>
>>> If the allocation done in tcf_exts_init() failed,
>>> we end up with a NULL pointer in exts->actions.
>> ...
>>> diff --git a/net/sched/cls_api.c b/net/sched/cls_api.c
>>> index
>>> efd3cfb80a2ad775dc8ab3c4900bd73d52c7aaad..9aef93300f1c11791acbb9262dfe77996872eafe
>>> 100644
>>> --- a/net/sched/cls_api.c
>>> +++ b/net/sched/cls_api.c
>>> @@ -3027,8 +3027,10 @@ static int tc_dump_chain(struct sk_buff *skb, struct
>>> netlink_callback *cb)
>>> void tcf_exts_destroy(struct tcf_exts *exts)
>>> {
>>> #ifdef CONFIG_NET_CLS_ACT
>>> - tcf_action_destroy(exts->actions, TCA_ACT_UNBIND);
>>> - kfree(exts->actions);
>>> + if (exts->actions) {
>>
>> I think it is _slightly_ better to check exts->nr_actions!=0 here,
>> as it would help exts->actions!=NULL&& exts->nr_actions==0
>> cases too.
>>
>> What do you think?
>
> Alternatively, since tcf_exts_destroy() now takes NULL, and so
> obviously does kfree() - perhaps tcf_action_destroy() should
> return early if actions are NULL?
>
I do not have any preference really, this is slow path and was trying to
fix a crash.
tcf_action_destroy() makes me nervous, since it seems to be able to break its
loop
in case __tcf_idr_release() returns an error. This means that some actions will
never be release.
