On 04/09/2018 07:58 AM, David Miller wrote: > From: Eric Dumazet <eduma...@google.com> > Date: Mon, 9 Apr 2018 06:43:27 -0700 > >> syzbot/KMSAN reported that p->dtime was read while it was >> not yet initialized in : >> >> delta = (__u32)jiffies - p->dtime; >> if (delta < ttl || !refcount_dec_if_one(&p->refcnt)) >> gc_stack[i] = NULL; >> >> This is a false positive, because the inetpeer wont be erased >> from rb-tree if the refcount_dec_if_one(&p->refcnt) does not >> succeed. And this wont happen before first inet_putpeer() call >> for this inetpeer has been done, and ->dtime field is written >> exactly before the refcount_dec_and_test(&p->refcnt). >> >> The KMSAN report was : > ... >> Signed-off-by: Eric Dumazet <eduma...@google.com> >> Reported-by: syzbot <syzkal...@googlegroups.com> > > Applied, but it looks like we are just adding assignments simply > to placate these reports when the tools and facilities cannot > see through the logic properly. >
To be fair, this is because the check on ->dtime should be done a second time after the refcount_dec_if_one(&p->refcnt) It is a tiny race, and we do not really care given nature of inetpeer cache, best effort, and DDOS candidate anyway. If we purge one entry too soon, this is not a big deal. I believe tool is fine.
