[NEIGH]: Fix race between pneigh deletion and ipv6's ndisc_recv_ns (v3).

Proxy neighbors do not have any reference counting, so any caller
of pneigh_lookup (unless it's a netlink triggered add/del routine)
should _not_ perform any actions on the found proxy entry. 

There's one exception from this rule - the ipv6's ndisc_recv_ns() 
uses found entry to check the flags for NTF_ROUTER.

This creates a race between the ndisc and pneigh_delete - after 
the pneigh is returned to the caller, the nd_tbl.lock is dropped 
and the deleting procedure may proceed.

One of the fixes would be to add a reference counting, but this
problem exists for ndisc only. Besides such a patch would be too 
big for -rc4.

So I propose to introduce a __pneigh_lookup() which is supposed
to be called with the lock held and use it in ndisc code to check
the flags on alive pneigh entry.


Changes from v2:
As David noticed, Exported the __pneigh_lookup() to ipv6 module. 
The checkpatch generates a warning on it, since the EXPORT_SYMBOL 
does not follow the symbol itself, but in this file all the 
exports come at the end, so I decided no to break this harmony.

Changes from v1:
Fixed comments from YOSHIFUJI - indentation of prototype in header
and the pndisc_check_router() name - and a compilation fix, pointed
by Daniel - the is_routed was (falsely) considered as uninitialized
by gcc.

Signed-off-by: Pavel Emelyanov <xemul@openvz.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 23 insertions, 0 deletions

diff --git a/net/core/neighbour.c b/net/core/neighbour.c
index d9a02b2cc289..19b8e003f150 100644
--- a/net/core/neighbour.c
+++ b/net/core/neighbour.c
@@ -466,6 +466,28 @@ out_neigh_release:
         goto out;
 }
 
+struct pneigh_entry *__pneigh_lookup(struct neigh_table *tbl,
+                struct net *net, const void *pkey, struct net_device *dev)
+{
+        struct pneigh_entry *n;
+        int key_len = tbl->key_len;
+        u32 hash_val = *(u32 *)(pkey + key_len - 4);
+
+        hash_val ^= (hash_val >> 16);
+        hash_val ^= hash_val >> 8;
+        hash_val ^= hash_val >> 4;
+        hash_val &= PNEIGH_HASHMASK;
+
+        for (n = tbl->phash_buckets[hash_val]; n; n = n->next) {
+                if (!memcmp(n->key, pkey, key_len) &&
+                    (n->net == net) &&
+                    (n->dev == dev || !n->dev))
+                        break;
+        }
+
+        return n;
+}
+
 struct pneigh_entry * pneigh_lookup(struct neigh_table *tbl,
                                     struct net *net, const void *pkey,
                                     struct net_device *dev, int creat)
@@ -2803,6 +2825,7 @@ EXPORT_SYMBOL(neigh_table_init_no_netlink);
 EXPORT_SYMBOL(neigh_update);
 EXPORT_SYMBOL(pneigh_enqueue);
 EXPORT_SYMBOL(pneigh_lookup);
+EXPORT_SYMBOL_GPL(__pneigh_lookup);
 
 #ifdef CONFIG_ARPD
 EXPORT_SYMBOL(neigh_app_ns);