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

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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>
This commit is contained in:
Pavel Emelyanov 2008-03-24 14:48:59 -07:00 committed by David S. Miller
parent 8f3ea33a50
commit fa86d322d8
3 changed files with 45 additions and 4 deletions
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4
include/net/neighbour.h
View file

@ -218,6 +218,10 @@ 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);

23
net/core/neighbour.c
View file

@ -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);

22
net/ipv6/ndisc.c
View file

@ -676,6 +676,20 @@ static void ndisc_solicit(struct neighbour *neigh, struct sk_buff *skb)
}
}
static struct pneigh_entry *pndisc_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);
@ -692,7 +706,7 @@ static void ndisc_recv_ns(struct sk_buff *skb)
struct pneigh_entry *pneigh = NULL;
int dad = ipv6_addr_any(saddr);
int inc;
int is_router;
int is_router = 0;
if (ipv6_addr_is_multicast(&msg->target)) {
ND_PRINTK2(KERN_WARNING
@ -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 = pndisc_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;