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net: neigh: disallow transition to NUD_STALE if lladdr is unchanged in neigh_update() 

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 <hchunhui@mail.ustc.edu.cn>
Signed-off-by: Julian Anastasov <ja@ssi.bg>
Reviewed-by: Hannes Frederic Sowa <hannes@stressinduktion.org>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
He Chunhui 2016-07-26 06:16:52 +00:00 committed by David S. Miller
parent ee591f46a5
commit d1c2b5010d
1 changed files with 1 additions and 6 deletions
net/core
neighbour.c

7
net/core/neighbour.c
View File

@ -1060,8 +1060,6 @@ static void neigh_update_hhs(struct neighbour *neigh)
NEIGH_UPDATE_F_WEAK_OVERRIDE will suspect existing "connected" NEIGH_UPDATE_F_WEAK_OVERRIDE will suspect existing "connected"
lladdr instead of overriding it lladdr instead of overriding it
if it is different. if it is different.
It also allows to retain current state
if lladdr is unchanged.
NEIGH_UPDATE_F_ADMIN means that the change is administrative. NEIGH_UPDATE_F_ADMIN means that the change is administrative.
NEIGH_UPDATE_F_OVERRIDE_ISROUTER allows to override existing NEIGH_UPDATE_F_OVERRIDE_ISROUTER allows to override existing
@ -1150,10 +1148,7 @@ int neigh_update(struct neighbour *neigh, const u8 *lladdr, u8 new,
} else } else
goto out; goto out;
} else { } else {
if (lladdr == neigh->ha && new == NUD_STALE && if (lladdr == neigh->ha && new == NUD_STALE)
((flags & NEIGH_UPDATE_F_WEAK_OVERRIDE) ||
(old & NUD_CONNECTED))
)
new = old; new = old;
} }
} }