[PATCH 4.0 13/55] neigh: do not modify unlinked entries

Greg Kroah-Hartman
2015-07-08T08:18:25Z

From: Julian Anastasov <ja@ssi.bg>

[ Upstream commit 2c51a97f76d20ebf1f50fef908b986cb051fdff9 ]

The lockless lookups can return entry that is unlinked.
Sometimes they get reference before last neigh_cleanup_and_release,
sometimes they do not need reference. Later, any
modification attempts may result in the following problems:

1. entry is not destroyed immediately because neigh_update
can start the timer for dead entry, eg. on change to NUD_REACHABLE
state. As result, entry lives for some time but is invisible
and out of control.

2. __neigh_event_send can run in parallel with neigh_destroy
while refcnt=0 but if timer is started and expired refcnt can
reach 0 for second time leading to second neigh_destroy and
possible crash.

Thanks to Eric Dumazet and Ying Xue for their work and analyze
on the __neigh_event_send change.

Fixes: 767e97e1e0db ("neigh: RCU conversion of struct neighbour")
Fixes: a263b3093641 ("ipv4: Make neigh lookups directly in output packet path.")
Fixes: 6fd6ce2056de ("ipv6: Do not depend on rt->n in ip6_finish_output2().")
Cc: Eric Dumazet <eric.dumazet@gmail.com>
Cc: Ying Xue <ying.xue@windriver.com>
Signed-off-by: Julian Anastasov <ja@ssi.bg>
Acked-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
net/core/neighbour.c | 13 +++++++++++++
1 file changed, 13 insertions(+)

--- a/net/core/neighbour.c
+++ b/net/core/neighbour.c
@@ -971,6 +971,8 @@ int __neigh_event_send(struct neighbour
rc = 0;
if (neigh->nud_state & (NUD_CONNECTED | NUD_DELAY | NUD_PROBE))
goto out_unlock_bh;
+ if (neigh->dead)
+ goto out_dead;

if (!(neigh->nud_state & (NUD_STALE | NUD_INCOMPLETE))) {
if (NEIGH_VAR(neigh->parms, MCAST_PROBES) +
@@ -1027,6 +1029,13 @@ out_unlock_bh:
write_unlock(&neigh->lock);
local_bh_enable();
return rc;
+
+out_dead:
+ if (neigh->nud_state & NUD_STALE)
+ goto out_unlock_bh;
+ write_unlock_bh(&neigh->lock);
+ kfree_skb(skb);
+ return 1;
}
EXPORT_SYMBOL(__neigh_event_send);

@@ -1090,6 +1099,8 @@ int neigh_update(struct neighbour *neigh
if (!(flags & NEIGH_UPDATE_F_ADMIN) &&
(old & (NUD_NOARP | NUD_PERMANENT)))
goto out;
+ if (neigh->dead)
+ goto out;

if (!(new & NUD_VALID)) {
neigh_del_timer(neigh);
@@ -1239,6 +1250,8 @@ EXPORT_SYMBOL(neigh_update);
*/
void __neigh_set_probe_once(struct neighbour *neigh)
{
+ if (neigh->dead)
+ return;
neigh->updated = jiffies;
if (!(neigh->nud_state & NUD_FAILED))
return;