On Mon, 03 Mar 2014 15:49:56 +0100 Nikolay Aleksandrov <nikolay@xxxxxxxxxx> wrote: > On 03/03/2014 03:40 PM, Florian Westphal wrote: > > Nikolay Aleksandrov <nikolay@xxxxxxxxxx> wrote: > >> I stumbled upon this very serious bug while hunting for another one, > >> it's a very subtle race condition between inet_frag_evictor, > >> inet_frag_intern and the IPv4/6 frag_queue and expire functions (basically > >> the users of inet_frag_kill/inet_frag_put). > >> What happens is that after a fragment has been added to the hash chain but > >> before it's been added to the lru_list (inet_frag_lru_add), it may get > >> deleted (either by an expired timer if the system load is high or the > >> timer sufficiently low, or by the fraq_queue function for different > >> reasons) before it's added to the lru_list > > > > Sorry. Not following here, see below. > > > >> diff --git a/net/ipv4/inet_fragment.c b/net/ipv4/inet_fragment.c > >> index bb075fc9a14f..322dcebfc588 100644 > >> --- a/net/ipv4/inet_fragment.c > >> +++ b/net/ipv4/inet_fragment.c > >> @@ -278,9 +278,10 @@ static struct inet_frag_queue *inet_frag_intern(struct netns_frags *nf, > >> > >> atomic_inc(&qp->refcnt); > >> hlist_add_head(&qp->list, &hb->chain); > >> + inet_frag_lru_add(nf, qp); > >> spin_unlock(&hb->chain_lock); > >> read_unlock(&f->lock); > > > > If I understand correctly your're saying that qp can be free'd on > > another/cpu timer right after dropping the locks. But how is it > > possible? > > > > ->refcnt is bumped above when arming the timer (before dropping chain > > lock), so even if the frag_expire timer fires instantly it should not > > free qp. > > > > What am I missing? > > > > Thanks, > > Florian > > > An important point is that inet_frag_kill removes both the timer's refcnt and > has an unconditional atomic_dec to remove the original/guarding refcnt, so it > basically removes everything that's in the way. It sound like we might have a refcnt problem... Do we need an extra refcnt for maintaining elements the LRU list? -- Best regards, Jesper Dangaard Brouer MSc.CS, Sr. Network Kernel Developer at Red Hat Author of http://www.iptv-analyzer.org LinkedIn: http://www.linkedin.com/in/brouer -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html