On 26.07.2016 08:16, Chunhui He wrote: > NUD_STALE is used when the caller(e.g. arp_process()) can't guarantee > neighbour reachability. If the entry was NUD_VALID and lladdr is unchanged, > the entry state should not be changed. > > Currently the code puts an extra "NUD_CONNECTED" condition. So if old state > was NUD_DELAY or NUD_PROBE (they are NUD_VALID but not NUD_CONNECTED), the > state can be changed to NUD_STALE. > > This may cause problem. Because NUD_STALE lladdr doesn't guarantee > reachability, when we send traffic, the state will be changed to > NUD_DELAY. In normal case, if we get no confirmation (by dst_confirm()), > we will change the state to NUD_PROBE and send probe traffic. But now the > state may be reset to NUD_STALE again(e.g. by broadcast ARP packets), > so the probe traffic will not be sent. This situation may happen again and > again, and packets will be sent to an non-reachable lladdr forever. > > The fix is to remove the "NUD_CONNECTED" condition. After that the > "NEIGH_UPDATE_F_WEAK_OVERRIDE" condition (used by IPv6) in that branch will > be redundant, so remove it. > > This change may increase probe traffic, but it's essential since NUD_STALE > lladdr is unreliable. To ensure correctness, we prefer to resolve lladdr, > when we can't get confirmation, even while remote packets try to set > NUD_STALE state. > > Signed-off-by: Chunhui He <hchun...@mail.ustc.edu.cn> > --- > v2: > - change title from "net: neigh: disallow state transition DELAY->STALE in > neigh_update()" > - remove "NUD_CONNECTED" condition instead of "NUD_CONNECTED | NUD_DELAY" > - remove "NEIGH_UPDATE_F_WEAK_OVERRIDE" condition
Reviewed-by: Hannes Frederic Sowa <han...@stressinduktion.org> Thanks!
