Hi Liping, On Wed, Sep 28, 2016 at 11:13 AM, Liping Zhang <zlpnobody@xxxxxxxxx> wrote: > 2016-09-28 11:08 GMT+08:00 Liping Zhang <zlpnobody@xxxxxxxxx>: >> Hi Feng, >> >> 2016-09-28 9:23 GMT+08:00 Feng Gao <gfree.wind@xxxxxxxxx>: >>> Hi Aaraon, >>> >>> On Tue, Sep 27, 2016 at 9:38 PM, Aaron Conole <aconole@xxxxxxxxxx> wrote: >>>> It's possible for nf_hook_entry_head to return NULL if two >>>> nf_unregister_net_hook calls happen simultaneously with a single hook >>> >>> The critical region of nf_unregister_net_hook is protected by &nf_hook_mutex. >>> When it would be called simultaneously? >> >> This is unrelated to race condition. >> >> Suppose that only the last nf_hook_entry exist, and two callers want to do >> un-register work. >> >> The first one will remove it successfully, after the end of the work, the >> second one will enter the critical section, but it will see the NULL pointer. >> Because the last nf_hook_entry was already removed by the first one. >> >>> >>> Regards >>> Feng >>> >>>> entry in the list. This fix ensures that no null pointer dereference >>>> could occur when such a race happens. >>>> >>>> Signed-off-by: Aaron Conole <aconole@xxxxxxxxxx> > > I read the commit log again, I think the description here is a > little confusing indeed. Yes. I doesn't check if the list head always exists, just learn the patch from commit log. It confuses me indeed. Regards Feng -- To unsubscribe from this list: send the line "unsubscribe netfilter-devel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
