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Message-ID: <47CFD2ED.3060207@openvz.org>
Date: Thu, 06 Mar 2008 14:18:05 +0300
From: Pavel Emelyanov <xemul@...nvz.org>
To: David Miller <davem@...emloft.net>
CC: Linux Netdev List <netdev@...r.kernel.org>
Subject: [PATCH][NEIGH]: Fix race between pneigh deletion and ipv6's ndisc_recv_ns.
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.
If this is OK, is there a real need in proxy neighbors reference
counting for 2.6.26 :) ?
Signed-off-by: Pavel Emelyanov <xemul@...nvz.org>
---
diff --git a/include/net/neighbour.h b/include/net/neighbour.h
index ebbfb50..cca1904 100644
--- a/include/net/neighbour.h
+++ b/include/net/neighbour.h
@@ -218,6 +218,8 @@ extern unsigned long neigh_rand_reach_time(unsigned long base);
extern void pneigh_enqueue(struct neigh_table *tbl, struct neigh_parms *p,
struct sk_buff *skb);
extern struct pneigh_entry *pneigh_lookup(struct neigh_table *tbl, struct net *net, const void *key, struct net_device *dev, int creat);
+extern struct pneigh_entry *__pneigh_lookup(struct neigh_table *tbl,
+ struct net *net, const void *key, struct net_device *dev);
extern int pneigh_delete(struct neigh_table *tbl, struct net *net, const void *key, struct net_device *dev);
extern void neigh_app_ns(struct neighbour *n);
diff --git a/net/core/neighbour.c b/net/core/neighbour.c
index d9a02b2..c97bf5b 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)
diff --git a/net/ipv6/ndisc.c b/net/ipv6/ndisc.c
index 0d33a7d..bb72ef4 100644
--- a/net/ipv6/ndisc.c
+++ b/net/ipv6/ndisc.c
@@ -676,6 +676,20 @@ static void ndisc_solicit(struct neighbour *neigh, struct sk_buff *skb)
}
}
+static struct pneigh_entry *neigh_check_router(struct net_device *dev,
+ struct in6_addr *addr, int *is_router)
+{
+ struct pneigh_entry *n;
+
+ read_lock_bh(&nd_tbl.lock);
+ n = __pneigh_lookup(&nd_tbl, &init_net, addr, dev);
+ if (n != NULL)
+ *is_router = (n->flags & NTF_ROUTER);
+ read_unlock_bh(&nd_tbl.lock);
+
+ return n;
+}
+
static void ndisc_recv_ns(struct sk_buff *skb)
{
struct nd_msg *msg = (struct nd_msg *)skb_transport_header(skb);
@@ -790,8 +804,8 @@ static void ndisc_recv_ns(struct sk_buff *skb)
if (ipv6_chk_acast_addr(dev, &msg->target) ||
(idev->cnf.forwarding &&
(ipv6_devconf.proxy_ndp || idev->cnf.proxy_ndp) &&
- (pneigh = pneigh_lookup(&nd_tbl, &init_net,
- &msg->target, dev, 0)) != NULL)) {
+ (pneigh = neigh_check_router(dev, &msg->target,
+ &is_router)) != NULL)) {
if (!(NEIGH_CB(skb)->flags & LOCALLY_ENQUEUED) &&
skb->pkt_type != PACKET_HOST &&
inc != 0 &&
@@ -812,7 +826,7 @@ static void ndisc_recv_ns(struct sk_buff *skb)
goto out;
}
- is_router = !!(pneigh ? pneigh->flags & NTF_ROUTER : idev->cnf.forwarding);
+ is_router = !!(pneigh ? is_router : idev->cnf.forwarding);
if (dad) {
struct in6_addr maddr;
--
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