Subject: [PATCH][NEIGH]: Fix race between pneigh deletion and ipv6's ndisc_recv_ns - V2 From: Pavel Emelyanov 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 Signed-off-by: Daniel Lezcano --- include/net/neighbour.h | 2 ++ net/core/neighbour.c | 22 ++++++++++++++++++++++ net/ipv6/ndisc.c | 23 +++++++++++++++++++---- 3 files changed, 43 insertions(+), 4 deletions(-) Index: net-2.6.26/include/net/neighbour.h =================================================================== --- net-2.6.26.orig/include/net/neighbour.h +++ net-2.6.26/include/net/neighbour.h @@ -218,6 +218,8 @@ extern unsigned long neigh_rand_reach_t 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); Index: net-2.6.26/net/core/neighbour.c =================================================================== --- net-2.6.26.orig/net/core/neighbour.c +++ net-2.6.26/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) Index: net-2.6.26/net/ipv6/ndisc.c =================================================================== --- net-2.6.26.orig/net/ipv6/ndisc.c +++ net-2.6.26/net/ipv6/ndisc.c @@ -659,6 +659,21 @@ static void ndisc_solicit(struct neighbo } } +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, dev->nd_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); @@ -675,7 +690,7 @@ static void ndisc_recv_ns(struct sk_buff 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 @@ -774,8 +789,8 @@ static void ndisc_recv_ns(struct sk_buff if (ipv6_chk_acast_addr(dev, &msg->target) || (idev->cnf.forwarding && (ipv6_devconf.proxy_ndp || idev->cnf.proxy_ndp) && - (pneigh = pneigh_lookup(&nd_tbl, dev->nd_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 && @@ -796,7 +811,7 @@ static void ndisc_recv_ns(struct sk_buff 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;