Re: net/packet: use-after-free in packet_rcv_fanout

On (02/10/17 10:00), Cong Wang wrote:

My understanding about the race here is packet_release() doesn't
wait for flying packets correctly, which leads to a flying packet still
refers to the struct sock which is being released.

This could happen because struct packet_fanout is refcn'ted, it is

   :

At least I believe this explains the crash Dmitry reported.

hmm, the proof of the pudding is in the eating- would be good to 
be able to reliably reproduce this somewhere (thus proving that
root-cause analysis is rock-solid), maybe by introducing artificial
delays to slow down paths..

I'm travelling at the moment but may be able to give this (try
to reproduce it reliably) next week.

--Sowmini